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Rumors => Lenses => Topic started by: JonB8305 on February 20, 2013, 08:56:25 PM

Title: Why aren't zoom lenses faster than 2.8?
Post by: JonB8305 on February 20, 2013, 08:56:25 PM
Is it a business decision (ie dont want to canabalize the prime market) or a technical limitation (physically can't do it with current tech) or cost issue (technical difficulties would require that the lens be priced too high for target market)?
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: viggen61 on February 20, 2013, 09:06:31 PM
Mostly the third, I'd think. If a 70-200 f/2.8 costs $1500, imagine what even a 1.8 would cost!

Maybe a bit of the first, but technically, I'm sure it's well within the capabilities of a Canon or Nikon. But would you really want to lug about an 8 lb zoom? Ok, maybe the 200-400 f/4L 1.4x...  8)
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: wickidwombat on February 20, 2013, 09:38:20 PM
I'd pay super tele prices for a sharp wide open 35-85 f1.8 or f2 L IS zoom ;D
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: JonB8305 on February 20, 2013, 10:57:01 PM
are lens prices typically a function of the manufacturing costs being high?
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: JonB8305 on February 20, 2013, 10:57:24 PM
I'd pay super tele prices for a sharp wide open 35-85 f1.8 or f2 L IS zoom ;D

That would be pretty sweet.
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: bdunbar79 on February 20, 2013, 11:03:00 PM
I think the physical limitation to making an f/1.8 zoom, say a 16-35 f/1.8 or even a 24-70 f/1.8, would require a lot more glass.  And that more glass would require a lot more money for you to pay :).
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: JonB8305 on February 20, 2013, 11:05:45 PM
I think the physical limitation to making an f/1.8 zoom, say a 16-35 f/1.8 or even a 24-70 f/1.8, would require a lot more glass.  And that more glass would require a lot more money for you to pay :).

ahhhh... tradeoffs
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: JonB8305 on February 20, 2013, 11:07:45 PM
Canon used to make a 25-100 F/1.8
http://www.visualproducts.com/storeProductDetail02.asp?productID=152&Cat=3&Cat2=49 (http://www.visualproducts.com/storeProductDetail02.asp?productID=152&Cat=3&Cat2=49)
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: robbymack on February 20, 2013, 11:14:14 PM
They certainly can (thanks for the link above, but mfd of 8 ft  :o) but I don't think anyone would like to carry one around. A zoom, at least for me, is about convenience, so while an ultra fast zoom would be great, it would cost a small fortune and be a b*tch to carry around.  All you have to do is troll this forum and you'll constantly see folks opting for the f4 versions of many a zoom simply because the 2.8 is already heavy so an even faster zoom would presumably be even heavier.
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: wickidwombat on February 20, 2013, 11:30:51 PM
I think a 35 to 85 f1.8 could be done in a size smaller than a 200 f2L and probably a lower weight
possibly even as small as an 82mm filter I think by limiting the wide end to 35 you are not running into all the wide angle problems super zooms encounter
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: BrandonKing96 on February 21, 2013, 01:31:33 AM
Possible, but I don't see your reason for wanting them as it massively adds to cost (the glass they have to put in) and it just gets heavier and heavier, even though they're sharp as heck now and 2.8 is really good for zooming.  I was surprised to find my 24-70 II A LOT heavier than my 70-200 f/4 IS. 
As you know, it'd be a better option to go for a prime to get apertures larger than f/2.8 due to the lighter construction :)

But then again, I'd probably be VERY tempted into buying a 70-200 f/1.8L IS
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: Hobby Shooter on February 21, 2013, 01:36:20 AM
I posted a similar question a few weeks ago, I couldn't find that thread now but will have a look again to see if I can get it for you. As I understand it, a 70-200 f/1.8 for example would be just too big to carry and too expensive to buy basically.
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: Menace on February 21, 2013, 01:40:44 AM
Likely to be too heavy and very expensive - possible but not very probable.

Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: Hobby Shooter on February 21, 2013, 01:49:54 AM
Found it http://www.canonrumors.com/forum/index.php?topic=12379.0 (http://www.canonrumors.com/forum/index.php?topic=12379.0)
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: alexanderferdinand on February 21, 2013, 02:24:03 AM
Would be

very expensive
very heavy

Although I am a male, 6' 4", I am glad the 70-200/2,8 IS II is not heavier, because of carrying and handholding.
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: sandymandy on February 21, 2013, 02:35:09 AM
Zooms are supposed to be allround lenses, easy to carry and ready for all situations (kind of). Having a bigger aperture would make the lenses big and  bulky and not comfortable to carry around. For example if  you want 2.0 at 200mm the lens would have to be 10cm diameter. 70mm would require a 50mm diameter for f/1.4.
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: K3nt on February 21, 2013, 02:54:00 AM
It is quite easy actually. If you want to know what size it would require just divide the focal length with the required f-stop and you'll see what size the front element diameter would be. So, for a 100-400mm f/1.2 the front element would be 33,3cm in diameter.  :D

If you divide the focal length with the diameter of the front element you'll get the maximum f-stop for that lens.
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: bycostello on February 21, 2013, 03:20:06 AM
cost, weight and demand
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: Hillsilly on February 21, 2013, 03:53:16 AM
Olympus make a 14-35 f/2 and a 35-100 f/2.  Both are $2k+ and only cover a four thirds size sensor.  These lenses are big, but not that big.  With their superior economies of scale and production capabilities, Canon could make similar EF-S lenses without too much of a size, weight or cost penalty.  But is there a market for $2k+ EF-S lenses? 
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: brad goda on February 21, 2013, 03:54:32 AM
wow... the cost and weight!!!
and everyone is wanting that f1.8 to be dead sharp wide open!!! LOL.
so that means its not easy to build... it would have to be OVER built.!
like the new zeiss prime 55mm 1.4... that is over built... massive image circle + good deisgn =
huge sweet spot for sharpness to cover full frame...
In any form UWA ... standard zoom or telephoto zoom its a reach to think our industry would support it... only cinema zooms have that sort of at whatever it costs... its made... and bought.

besides... at 500.00 for super telephoto replacement 2.8 lens hood... can you imagine for 1.8...??

yah great for event photos... an 8-13lb camera + lens...
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: rs on February 21, 2013, 03:55:25 AM
Zooms are supposed to be allround lenses, easy to carry and ready for all situations (kind of). Having a bigger aperture would make the lenses big and  bulky and not comfortable to carry around. For example if  you want 2.0 at 200mm the lens would have to be 10cm diameter. 70mm would require a 50mm diameter for f/1.4.
That's the simple way of looking at it, but look at the reality of what already exists in terms of zooms and primes - the situation is even worse than you predict, so we end up with something that is all but impossible to afford, carry, or use.

Take the 70-200/2.8L (non IS) vs the 200/2.8L II - when fully zoomed, the 70-200 offers the same unstabilised 200/2.8 as the prime. A 200/2.8 theoretically needs a 71.4mm aperture, and the prime indeed has a 72mm filter thread, and is 136mm length, weighing in at 765g. The zoom has a 77mm filter, 194mm long, and weighs 1310g.

Taking those increases over an existing 200/2.8 and applying them to the 200/2 IS lens to end up with a theoretical 70-200/2.0 IS lens, and you get a 136mm diameter, 296mm length, 4.3kg lens. And then there's the price factor between the prime and zoom too. It would cost (years after the introduction price tax disappears, like it has on the 200/2.8, 70-200/2.8 and 200/2) something in the region of £7000 - so lets call it comfortably more than £10,000 at introduction. There clearly wouldn't be a market for something like that.

However, a very limited zoom range around the 50mm mark would be simpler to make faster - 50mm after all does seem to be the easiest focal length to make fast (think of the 50/1.0 L, and also how small the current 50/1.4 is), so a 40-60/2.0 probably isn't pushing the boundaries of what's possible. But with such a small zoom range, why not just get a much cheaper, smaller and optically better 50 instead?

Having said that, smaller imaging circle lenses exist faster than f2.8 - take the Olympus m4/3 35-100/2.0 lens. But that is an equivalent of a 70-200/4.0 FF lens. And that Canon 25-100/1.8 is a 16mm lens (crop factor of 3.4), so in FF terms its a 85-340/6.1 lens.
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: Radiating on February 21, 2013, 03:58:45 AM
The Canon. 25-100mm lens was a cinema lens designed for a format that was much smaller yet was very heavy, about the size if a 70-200mm f/4.0 is. The sensor size was around 1/4 of full frame so while yes such a lens is possible it would be huge and expensive.

Say if you wanted a 28-85mm f/2.0. It would cost at least $10,000 based on Canons manufacturing costs for lenses of similar size, weigh 4-6 lbs and would use 120mm filters, and be over 12 inches long.

The market would be so small for such a lens Canon would likely change $20,000 or more.

Simply put such a product would be very convention defying.

You can also buy a number of f/3.5 zooms for medium format cameras which are equivalent for f/2.2 lenses on full frame. Leica makes one like that, that's equivalent to a 20-60mm lens.

Personally I think a 70-200mm f/2.0 zoom for 7k is realistic and would sell.
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: neuroanatomist on February 21, 2013, 08:52:04 AM
It is quite easy actually. If you want to know what size it would require just divide the focal length with the required f-stop and you'll see what size the front element diameter would be. So, for a 100-400mm f/1.2 the front element would be 33,3cm in diameter. 

Actaully, that 'rule' applies to telephoto lens designs but not all lens designs.  Else, the front element of the 16-35mm f/2.8L would be only 1.25 cm in diameter. 
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: JonB8305 on February 21, 2013, 09:06:57 PM
Zooms are supposed to be allround lenses, easy to carry and ready for all situations (kind of). Having a bigger aperture would make the lenses big and  bulky and not comfortable to carry around. For example if  you want 2.0 at 200mm the lens would have to be 10cm diameter. 70mm would require a 50mm diameter for f/1.4.
That's the simple way of looking at it, but look at the reality of what already exists in terms of zooms and primes - the situation is even worse than you predict, so we end up with something that is all but impossible to afford, carry, or use.

Take the 70-200/2.8L (non IS) vs the 200/2.8L II - when fully zoomed, the 70-200 offers the same unstabilised 200/2.8 as the prime. A 200/2.8 theoretically needs a 71.4mm aperture, and the prime indeed has a 72mm filter thread, and is 136mm length, weighing in at 765g. The zoom has a 77mm filter, 194mm long, and weighs 1310g.

Taking those increases over an existing 200/2.8 and applying them to the 200/2 IS lens to end up with a theoretical 70-200/2.0 IS lens, and you get a 136mm diameter, 296mm length, 4.3kg lens. And then there's the price factor between the prime and zoom too. It would cost (years after the introduction price tax disappears, like it has on the 200/2.8, 70-200/2.8 and 200/2) something in the region of £7000 - so lets call it comfortably more than £10,000 at introduction. There clearly wouldn't be a market for something like that.

However, a very limited zoom range around the 50mm mark would be simpler to make faster - 50mm after all does seem to be the easiest focal length to make fast (think of the 50/1.0 L, and also how small the current 50/1.4 is), so a 40-60/2.0 probably isn't pushing the boundaries of what's possible. But with such a small zoom range, why not just get a much cheaper, smaller and optically better 50 instead?

Having said that, smaller imaging circle lenses exist faster than f2.8 - take the Olympus m4/3 35-100/2.0 lens. But that is an equivalent of a 70-200/4.0 FF lens. And that Canon 25-100/1.8 is a 16mm lens (crop factor of 3.4), so in FF terms its a 85-340/6.1 lens.

Thanks for the knowledge, fascinating post.
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: Hobby Shooter on February 21, 2013, 09:37:03 PM
It is quite easy actually. If you want to know what size it would require just divide the focal length with the required f-stop and you'll see what size the front element diameter would be. So, for a 100-400mm f/1.2 the front element would be 33,3cm in diameter. 

Actaully, that 'rule' applies to telephoto lens designs but not all lens designs.  Else, the front element of the 16-35mm f/2.8L would be only 1.25 cm in diameter.
That's typical, I was just starting to get it and now you complicate things again  ;)
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: Lawliet on February 21, 2013, 09:38:33 PM
Canon used to make a 25-100 F/1.8

Keep in mind that this is a cine lens - about the image circle of an EF-s.
If one took a common 70-200/2.8 and welded an inverse TC2 to it he'd get an 35-100/1.4. Makes me think of the fast 4/3rds zooms...
Now the same trick for EF would require a f/2.8 zoom for medium forma (6x9 should work, 6x7 feels like a tight fit)as a baseline. Not pretty.
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: East Wind Photography on February 21, 2013, 09:42:02 PM
It would make them too heavy to be practical.  The 70-200L 2.8 is already two bricks.
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: SiliconVoid on February 21, 2013, 10:13:46 PM
If you research the primary cons for any premium lens, regardless of brand, you will see 'size' 'weight' and 'cost'..
How well received do you think a 70-200mm with an 6" objective lens, ~6lb heft, and ~$5,000 price tag would be??
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: RLPhoto on February 21, 2013, 10:39:34 PM
The 70-200L II is already pretty hefty, I could only imagine a 1.8 lens.
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: Mt Spokane Photography on February 21, 2013, 10:56:57 PM
As lenses get larger apertures, particularly at shorter focal lengths, it becomes difficult to keep the edges sharp, eliminate field of curvature, etc.  This means larger diameter glass and more elements.
Since the cost to grind glass increases with size, cost of large diameter lens elements skyrockets.  Now, add several more expensive elements to try and correct distortions, CA, etc, and the price gets out of control.
For expensive lenses, the market is much smaller, so development and tooling charges are amortized over just a few lenses, maybe 1000 more or less.  Spread that $1 million over 1000 lenses, and just the development cost is $10,000 per lens, and add another $10,000 manufacturing cost, and you have a lens that sells for $40,000, which is what the low volume cinema lenses sell for.
 
For a lens that sells 100,000 copies, the amortization might be $100 each, and the price is more reasonable.
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: EvillEmperor on February 21, 2013, 11:32:36 PM
How come the G15 is a 1.8-2.8 and doesn't weigh a 100lbs? I actually wouldn't mind a variable aperature zoom like the G15's. why don't they do that?
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: Zlatko on February 22, 2013, 12:13:11 AM
How come the G15 is a 1.8-2.8 and doesn't weigh a 100lbs? I actually wouldn't mind a variable aperature zoom like the G15's. why don't they do that?
The G15 has a tiny sensor, so the lens can be small.  It is still impressive.
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: BrandonKing96 on February 22, 2013, 12:40:50 AM
How come the G15 is a 1.8-2.8 and doesn't weigh a 100lbs? I actually wouldn't mind a variable aperature zoom like the G15's. why don't they do that?
Completely different sensor. 
In relation to the actual question, there ARE zooms faster than f/2.8, just for other sensors. 
An f/2.8 lens on a medium format camera will be completely different to a 35mm camera, and different in a micro 4/3 sensor.
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: K3nt on February 22, 2013, 02:04:54 AM
It is quite easy actually. If you want to know what size it would require just divide the focal length with the required f-stop and you'll see what size the front element diameter would be. So, for a 100-400mm f/1.2 the front element would be 33,3cm in diameter. 

Actaully, that 'rule' applies to telephoto lens designs but not all lens designs.  Else, the front element of the 16-35mm f/2.8L would be only 1.25 cm in diameter.

Not to worry. The formula is pretty much correct. But there are other factors that come in to play. But as a rule of thumb it works good. It does not take in to account the convex and lens shapes required for UWA lenses for example, as pointed out. If you did make a straight 35mm by f2.8 you could theoretically get away with a 1.25cm diameter, but that's not 100% of the story. :)
That's typical, I was just starting to get it and now you complicate things again  ;)
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: rs on February 22, 2013, 02:44:02 AM
How come the G15 is a 1.8-2.8 and doesn't weigh a 100lbs? I actually wouldn't mind a variable aperature zoom like the G15's. why don't they do that?
The G15 has a relatively small sensor with a 4.6x crop factor, and the lens as a result has a very small imaging circle. In 35mm terms, its 6.1-30.5/1.8-2.8 lens is the equivalent of a 28-140/8.3-12.9 lens. Nothing too special. Small imaging circle lenses have been doing this for years - most camcorders with tiny 1/6" sensors have quite big zoom ranges, yet they open up to about f1.8 at the wide end.

But your question about variable aperture makes sense. These constant aperture lenses such as the 70-200's are pushing the limits at 200mm due to the entrance pupil opening up to almost the size of the front element, but down at 70 you get the impression they're held back. It probably would be possible with just some minor tweaks to make a 70-200/2.0-2.8 lens.

As around 50mm seems to be about the sweet spot for easy to make large apertures, zooms at the other end of the range such as 16-35's might be possible with f2.8 at 16mm, and getting slightly larger, again to about f2.0 at around the 35mm mark.
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: VirtualRain on February 22, 2013, 03:41:38 AM
Canon makes a wicked 35-3500mm f1.7 IS lens for HDTV... The only problem? You need a trunk to carry it and it costs $200K  ;D

http://www.canon.com/premium-lib/movie/t002/index.html (http://www.canon.com/premium-lib/movie/t002/index.html)

Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: Pagesphotography on February 22, 2013, 03:59:23 AM
I think it would be crazy expensive, and crazy heavy...

However, I'm in for a 8-600 f/1.2.  I could probably settle for a 1.4 if I have too.
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: rs on February 22, 2013, 04:18:02 AM
Canon makes a wicked 35-3500mm f1.7 IS lens for HDTV... The only problem? You need a trunk to carry it and it costs $200K  ;D

http://www.canon.com/premium-lib/movie/t002/index.html (http://www.canon.com/premium-lib/movie/t002/index.html)
It looks like its this lens you've found:

http://www.canon.co.uk/broadcast/tv_lenses/studio_field_lenses/DIGISUPER_100_xs/index.aspx?specs=1 (http://www.canon.co.uk/broadcast/tv_lenses/studio_field_lenses/DIGISUPER_100_xs/index.aspx?specs=1)

9.3-930mm/1.7-4.7, designed for a 2/3" sensor. That's a 3.93x crop factor to convert to 35mm terms, so its effectively a 36.5 to 3650mm lens, with an aperture varying between f6.6 and f18.4 - very impressive stuff (especially having a 100x zoom and being able to crop into an area just 1.38cm x 0.78cm with its built in 2x TC enabled), but it doesn't fit the bill as being equivalent to a FF zoom with an effective aperture bigger the f2.8.

Going bigger seems to be the only option. A lens like the Hasselblad 50-110/3.5-4.5 (http://www.adorama.com/HSHC50110.html) seems to be a good bet. In 35mm speak its f2.5 at the wide end of its focal range.
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: Zlatko on February 23, 2013, 09:10:57 PM
9.3-930mm/1.7-4.7, designed for a 2/3" sensor. That's a 3.93x crop factor to convert to 35mm terms, so its effectively a 36.5 to 3650mm lens, with an aperture varying between f6.6 and f18.4 - very impressive stuff (especially having a 100x zoom and being able to crop into an area just 1.38cm x 0.78cm with its built in 2x TC enabled), but it doesn't fit the bill as being equivalent to a FF zoom with an effective aperture bigger the f2.8.

Wow, it weighs 52 pounds and costs $166,769.95!
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: Radiating on February 23, 2013, 09:30:22 PM
How come the G15 is a 1.8-2.8 and doesn't weigh a 100lbs? I actually wouldn't mind a variable aperature zoom like the G15's. why don't they do that?

Most photographers have a huge misunderstanding about this issue. Simply put the bigger the sensor is the bigger the lens, and the bigger the sensor and lens, the more light you get falling onto the sensor.

That f/1.8-f/2.8 lens on the g15  equivalent both in the amount of light it gathers and apparent background blur, and in every way that matters to a full frame:

f/10-f/16 lens.

Much less impressive.

To actually be equivalent to an f/1.8 lens on full frame the G15 would have to have an f/0.3 lens, which if using the same optical design would have a 29 centimeter front filter thread (11.4 inches in diamiter). It would look something like this in dimensions:

(http://www.kenrockwell.com/sigma/images/200-500mm/D3R_4567-460.jpg)

Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: Hillsilly on February 24, 2013, 12:09:45 AM
In 35mm terms, its 6.1-30.5/1.8-2.8 lens is the equivalent of a 28-140/8.3-12.9 lens. Nothing too special.

Don't want to go off topic, but in 35mm terms it is still an f/1.8 - 2.8 lens.  It might have an equivalent field of view as a 28-140mm lens.  But the shutter speed is based on the f/1.8 to 2.8 aperture, which is pretty good.  The equivalent background (or lack of) is what you'd expect from a 6.1 - 30.5mm lens (which is largely independent of sensor size).  That is, you'd have similar background blur at 30.5mm at f/2.8 on G15 as you would with a 16-35mm zoomed to 30.5mm at f/2.8 on a 5Diii.  And in dark shooting conditions, shooting macro, or when capturing action with the fastest possible shutter speed, the ability to have more in focus for a given aperture is sometimes just as important.  (And besides, in post production it is easier to blur a background than add more detail in).

In a round about way, just trying to say that the aperture range of a lens should be viewed independently of sensor size.  From there, most sensible photographers can use their own judgement as to whether a particular system/sensor size is suitable for their purpose.  Need more background in focus, shoot m43 or the G15.  Need more background blur, shoot medium format (or adjust in post production).  Need it just right, shoot full frame.

Imagine this scenario - Canon releases an EF-S 400mm f/4 with image quality, build and price equivalent to the EF 400mm f/5.6.  Even though some might say it is still a "f/5.6 equivalent", most people would instantly see the benefit of the faster aperture.
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: Radiating on February 24, 2013, 01:39:26 AM
In 35mm terms, its 6.1-30.5/1.8-2.8 lens is the equivalent of a 28-140/8.3-12.9 lens. Nothing too special.

Don't want to go off topic, but in 35mm terms it is still an f/1.8 - 2.8 lens.  It might have an equivalent field of view as a 28-140mm lens.  But the shutter speed is based on the f/1.8 to 2.8 aperture, which is pretty good.  The equivalent background (or lack of) is what you'd expect from a 6.1 - 30.5mm lens (which is largely independent of sensor size).  That is, you'd have similar background blur at 30.5mm at f/2.8 on G15 as you would with a 16-35mm zoomed to 30.5mm at f/2.8 on a 5Diii.  And in dark shooting conditions, shooting macro, or when capturing action with the fastest possible shutter speed, the ability to have more in focus for a given aperture is sometimes just as important.  (And besides, in post production it is easier to blur a background than add more detail in).

In a round about way, just trying to say that the aperture range of a lens should be viewed independently of sensor size.  From there, most sensible photographers can use their own judgement as to whether a particular system/sensor size is suitable for their purpose.  Need more background in focus, shoot m43 or the G15.  Need more background blur, shoot medium format (or adjust in post production).  Need it just right, shoot full frame.

Imagine this scenario - Canon releases an EF-S 400mm f/4 with image quality, build and price equivalent to the EF 400mm f/5.6.  Even though some might say it is still a "f/5.6 equivalent", most people would instantly see the benefit of the faster aperture.

People have been misled by this insane nonsense for years.


The "35mm equivalent" is what is really important and nothing else.

From a physics perspective the "35mm equivalent" is capturing identical information. What really matters is the geometry of the light hitting the sensor:

(http://upload.wikimedia.org/wikipedia/commons/0/0c/Depth_of_field_illustration.svg)

Generally the technical difficulty of achieving a particular geometry is INDEPENDENT of sensor size, meaning it's equally difficult to create a 17-55mm f/2.8 IS lens as it is to create a 24-105mm f/4.0 IS.

The front element of a 1/1.7" sensor lens that is 8-30mm f/0.3 lens would be 11.4 inches, and so would the front element of a 35mm sensor that has a 28-140mm f/1.8 lens.
 
Going back to the 35mm equivalent discussion, consider this:

On 7D compared the the 5D Mark III


The sensor is 1.6 x 1.6 times smaller.

35mm equivalent aperture - Multiply by (1.6 x 1.6 / 2 ) (an f stop is a base 2 log, so we divide by 2 to multiply between base 10 and base 2 if you were wondering, this just converts the number systems, nothing else)

35mm equivalent focal length - Multiply by 1.6

35mm equivalent ISO or light sensitivity - Multiply by (1.6 x 1.6) (bet you haven't heard of that,  but if you do the math the 7D's sensor amplifies the signal 1.6x1.6 times more at a given ISO than the 5D3)


The point is that people are often misled by manufacturers changing the geometry of a camera system, particularly putting in small sensors and then claiming otherwise impressive performance numbers which are incredibly misleading because you are measuring them on a different scale.

It's like saying:

I have a million dollars, and then failing to mention these are Zimbabwe dollars worth $20 not, American dollars.

Yes aperture ISO and focal length are fixed numbers, but so are monetary figures, and the most important thing even the most basic dealing of currency has is WHAT currency you're dealing with, and 99% of people require an "equivalent" frame of refference to understand foreign currency or need to do a conversion. Likewise with cameras, geometry (type of currency) is the most important thing when dealing with the performance of a camera system, and the first thing anyone needs to do is bring up a conversion to the local frame of reference, APS-C 35mm, whatever.

To respond to your post though, there is NO benefit to a 1 stop faster aperture on APS-C sensor vs full frame because they (more than) cancel each other out. You don't stop action any quicker at all, whatsoever, because remember the ISO is skewed too, so all you're doing is just turning up the ISO sensitivity in a roundabout way. You have been misled into thinking there is a benefit.
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: mb66energy on February 24, 2013, 01:55:21 AM
Is it a business decision (ie dont want to canabalize the prime market) or a technical limitation (physically can't do it with current tech) or cost issue (technical difficulties would require that the lens be priced too high for target market)?

There are hard physics facts which limit the chance to use well known designs to built such a lens.

Look at the cut views of e.g. a 2.8 70-200 II (see http://cweb.canon.jp/ef/lineup/tele-zoom/ef70-200-f28l-is-ii/img/spec/lens-construction.png (http://cweb.canon.jp/ef/lineup/tele-zoom/ef70-200-f28l-is-ii/img/spec/lens-construction.png) ). A f/2.0 lens should have a sqrt(2) larger diameter: scale the diameter AND THE THICKNESS of each lens by a factor of 1.41 - the tight spacing between the lenses doesn't allow that procedure to get a 2.0 lens.

Canon and all the other lens producers use exotic materials like high refractive index glass or lenses with special dispersion properties in their premium lenses. There is no headroom to change glass types. Let's dream about a glass type which has a refractive index of 2.5 or 3 without any dispersion and a super coating which increases the transmission to 99.9 %!

Than you have to recalculate the whole design including the 4, 5 or 6 lens groups which are positioned during zooming! This might introduce another 5 or 10 lenses to achieve good IQ and than you will loose more light due to reflections on the lenses ...

There are no physics killer facts to built a e.g. f/2.0 70-200 but physics will reduce IQ and/or increase massively the size (not only front element diameter but also the length). If you demand the IQ of the 2.8 70-200 II you will pay sth. between 50000 and 200000 $/€ for that lens - if it is possible to get such a high IQ. And than your third point factors in ...
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: rs on February 24, 2013, 05:12:15 AM
In 35mm terms, its 6.1-30.5/1.8-2.8 lens is the equivalent of a 28-140/8.3-12.9 lens. Nothing too special.

Don't want to go off topic, but in 35mm terms it is still an f/1.8 - 2.8 lens.  It might have an equivalent field of view as a 28-140mm lens.  But the shutter speed is based on the f/1.8 to 2.8 aperture, which is pretty good.  The equivalent background (or lack of) is what you'd expect from a 6.1 - 30.5mm lens (which is largely independent of sensor size).  That is, you'd have similar background blur at 30.5mm at f/2.8 on G15 as you would with a 16-35mm zoomed to 30.5mm at f/2.8 on a 5Diii.  And in dark shooting conditions, shooting macro, or when capturing action with the fastest possible shutter speed, the ability to have more in focus for a given aperture is sometimes just as important.  (And besides, in post production it is easier to blur a background than add more detail in).

In a round about way, just trying to say that the aperture range of a lens should be viewed independently of sensor size.  From there, most sensible photographers can use their own judgement as to whether a particular system/sensor size is suitable for their purpose.  Need more background in focus, shoot m43 or the G15.  Need more background blur, shoot medium format (or adjust in post production).  Need it just right, shoot full frame.

Imagine this scenario - Canon releases an EF-S 400mm f/4 with image quality, build and price equivalent to the EF 400mm f/5.6.  Even though some might say it is still a "f/5.6 equivalent", most people would instantly see the benefit of the faster aperture.
As Radiating pointed out, these smaller sensors have their amplification turned up to make their ISO ratings match the apertures. ISO 1600 on a G15 at f2.8 and 1/100th of a sec will match ISO 1600 on a 5D3 at f2.8 and 1/100th of a sec for exposure. But I'm sure no-one here disputes the fact that the smaller G15 sensor will produce much more noise at the same ISO's. Its simply because the amplification is turned up much higher to compensate for the much smaller imaging circle projecting much less light onto the sensor.

If the imaging circle is a fraction of the size, only a fraction of the light is projected onto the sensor.

While it is a 6.1-30.5/1.8-2.8 lens, it only covers a small imaging circle. To put it into context of a FF setup, it is factually incorrect to only scale up the focal length. The whole system has to get scaled up - so it becomes equivalent of a 28-140/8.3-12.9 lens in terms of focal length, DoF and quantity of light. And to complete that, you should also factor in what the sensor does - its ISO 80 to 12,800 sensor is the equivalent of a FF sensor which operates between ISO 1600 and 270,000.

I wouldn't get involved with blurring backgrounds in post, it will never look right. Instagram will never replace a good lens on a DSLR - just take the photo with the right camera and the right aperture. If you need more DoF with a FF setup, stop the lens down. Shooting at f32 will cause all sorts of diffraction issues, but so does f6.9 on a compact with an equal number of MP. You can always crank up the ISO and NR, and then set the sharpness to 10 in true compact style to ensure no fine detail remains.

Canon already have a 400/4 lens out there - its a FF DO lens, and costs five times as much as the f5.6 version.
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: elflord on February 24, 2013, 08:12:22 AM
As Radiating pointed out, these smaller sensors have their amplification turned up to make their ISO ratings match the apertures. ISO 1600 on a G15 at f2.8 and 1/100th of a sec will match ISO 1600 on a 5D3 at f2.8 and 1/100th of a sec for exposure. But I'm sure no-one here disputes the fact that the smaller G15 sensor will produce much more noise at the same ISO's. Its simply because the amplification is turned up much higher to compensate for the much smaller imaging circle projecting much less light onto the sensor.

The "amplification" is not "turned up" for the smaller sensor. A 6x4mm sensor is no more noisy (or "amplified") than a 6x4mm region of a 35mm sensor. Images from the smaller sensor are (theoretically) about as noisy as a crop from a larger sensor.

The reduction in noise has to do with sampling density and averaging, not amplification.
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: elflord on February 24, 2013, 08:28:40 AM
Generally the technical difficulty of achieving a particular geometry is INDEPENDENT of sensor size, meaning it's equally difficult to create a 17-55mm f/2.8 IS lens as it is to create a 24-105mm f/4.0 IS.

How about a 25mm f/0.7 lens for micro 4/3 ? Should that be comparably difficult to design and build as a 50mm f/1.4 full frame lens ?

Quote
To respond to your post though, there is NO benefit to a 1 stop faster aperture on APS-C sensor vs full frame because they (more than) cancel each other out. You don't stop action any quicker at all, whatsoever, because remember the ISO is skewed too, so all you're doing is just turning up the ISO sensitivity in a roundabout way. You have been misled into thinking there is a benefit.

The 400mm f/4 APS-C lens is "equivalent" to a 640mm f/6.4 lens. If you're distance limited, this really is preferable to a 400mm f/5.6 lens on full frame. You're right that it isn't "faster", but it is much longer than the 400mm f/5.6 full frame setup and almost as fast. Unfortunately, it's also quite a bit more expensive (not a whole lot cheaper to make the same lens for a smaller image circle)



Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: dolina on February 24, 2013, 08:41:41 AM
Cost, weight and complexity.
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: neuroanatomist on February 24, 2013, 08:45:48 AM
Elflord is correct, but the practical consequence remains the same.  Yes, when you state the 'FF equivalent' of a P&S lens, that small aperture applies to DoF not exposure.  But when considering shutter speed, you also need to consider ISO noise, and the relatively greater total light gathered by the larger sensor means less noise.  For example, ISO 640 on my S100 (which has a big sensor, for a P&S) is equivalent to ISO 3200 on a FF sensor (at least), so for a given necessary shutter speed, the 'fast' lens with the small sensor has no advantage in terms of noise - you can get the same shutter speed + noise output on FF.

The 400mm f/4 APS-C lens is "equivalent" to a 640mm f/6.4 lens. If you're distance limited, this really is preferable to a 400mm f/5.6 lens on full frame. You're right that it isn't "faster", but it is much longer than the 400mm f/5.6 full frame setup and almost as fast. Unfortunately, it's also quite a bit more expensive (not a whole lot cheaper to make the same lens for a smaller image circle)

The only real advantage to APS-C when 'focal length limited' is more MP in the final image.  From an IQ standpoint, the FF image cropped to APS-C FoV will be equivalent (for similar sensor generations), so if the 7-8.5 MP of the cropped FF image is sufficient for the intended output, the 'reach advantage' of a crop sensor is an illusion.  Of course...if you need the MP (24x36" prints, for example), the advantage is real. 
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: rs on February 24, 2013, 09:06:01 AM
The "amplification" is not "turned up" for the smaller sensor. A 6x4mm sensor is no more noisy (or "amplified") than a 6x4mm region of a 35mm sensor. Images from the smaller sensor are (theoretically) about as noisy as a crop from a larger sensor.

The reduction in noise has to do with sampling density and averaging, not amplification.
The smaller the photosite, the less light it gathers - therefore less electrical signal is generated, so it will need a higher amplification before being fed into the A/D converter. If we are comparing the 12MP G15 sensor to a 4.6x bigger diagonal 12MP D3s sensor, not only will the FF sensor with 21 times as much area collect 21 times as much light, but each photosite (pixel) will gather 21 times as much light - which means 21 times less amplification is needed to get the same ISO's - so ISO 1600 on FF equals ISO 80 on the G15 in terms of noise.

However, if we're talking about a 12MP G15 vs a 253MP FF (that same pixel size scaled up to FF), the amplification should be identical. That scenario is where your statement of sampling density and averaging are correct.

Usually its a combination of the two as the number of MP are almost never identical in these comparisons, as are the size of each individual pixel.

ps - I was talking about comparing the entire imaging system - FF sensor, FF lens uncropped to a compact camera
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: Hillsilly on February 24, 2013, 11:15:46 AM
To respond to your post though, there is NO benefit to a 1 stop faster aperture on APS-C sensor vs full frame because they (more than) cancel each other out. You don't stop action any quicker at all, whatsoever, because remember the ISO is skewed too, so all you're doing is just turning up the ISO sensitivity in a roundabout way.
Ok, Thanks.  So, assuming similar generation sensors, an APS-C based camera at ISO 100 at 1/100s would have similar (maybe even worse) image quality to a FF camera at ISO 200 at 1/100s.  Therefore no real speed benefit.  You'd just have more MPs, which may o may not be important.  Makes sense.

Although, we might still have to disagree on the conversion of apertures to 35mm equivalents. While converting the focal length to a 35mm equivalent makes sense (with the preponderance of different sensor sizes, it's good to have a commonly accepted way of understanding focal length), converting the aperture causes confusion.  At the same focus distance, a 30.5mm f/2.8 on a G15 has essentially the same background blur and requires the same shutter speed as a 30.5mm f/2.8 lens on a 7D and a 30.5mm f/2.8 lens on a 1Dx. In other words, a 30.5mm f/2.8 lens doesn't change any of its attributes when the sensor changes in size.   Therefore, there is no need to convert it to a 35mm equivalent.   The 30.5mm f2/8 is already a 35mm equivalent for every exposure and depth of field measurement.
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: neuroanatomist on February 24, 2013, 11:31:12 AM
Although, we might still have to disagree on the conversion of apertures to 35mm equivalents. While converting the focal length to a 35mm equivalent makes sense (with the preponderance of different sensor sizes, it's good to have a commonly accepted way of understanding focal length), converting the aperture causes confusion.  At the same focus distance, a 30.5mm f/2.8 on a G15 has essentially the same background blur and requires the same shutter speed as a 30.5mm f/2.8 lens on a 7D and a 30.5mm f/2.8 lens on a 1Dx. In other words, a 30.5mm f/2.8 lens doesn't change any of its attributes when the sensor changes in size.   Therefore, there is no need to convert it to a 35mm equivalent.   The 30.5mm f2/8 is already a 35mm equivalent for every exposure and depth of field measurement.

But...if the 1D X is taking a head shot, the 7D is cutting off the chin and hair, and the G15 is giving you just the eyes and nose - not exactly a flattering portrait.  A more relevant comparison is similarly-framed shots, and then the 'crop factor' effect on DoF applies (because with a smaller sensor and the same lens, you're further from the subject for the same framing).
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: rs on February 24, 2013, 11:41:37 AM
Although, we might still have to disagree on the conversion of apertures to 35mm equivalents. While converting the focal length to a 35mm equivalent makes sense (with the preponderance of different sensor sizes, it's good to have a commonly accepted way of understanding focal length), converting the aperture causes confusion.  At the same focus distance, a 30.5mm f/2.8 on a G15 has essentially the same background blur and requires the same shutter speed as a 30.5mm f/2.8 lens on a 7D and a 30.5mm f/2.8 lens on a 1Dx. In other words, a 30.5mm f/2.8 lens doesn't change any of its attributes when the sensor changes in size.   Therefore, there is no need to convert it to a 35mm equivalent.   The 30.5mm f2/8 is already a 35mm equivalent for every exposure and depth of field measurement.
If they're all cropped to the same angle of view, and printed at the same size. If not, we're talking about very different systems which cannot be compared in such simplistic terms.

If you use the effective focal length in 35mm terms to represent angle of view, lets get one thing straight - the aperture has to be adjusted too, otherwise you're no better than Panasonic's marketing department were with their FZ200:
(http://www3.picturepush.com/photo/a/12280946/1024/Picture-Box/highres-panasonic-lumix-fz200-8-1342452955.jpg)
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: Radiating on February 25, 2013, 01:16:12 PM
I resized and re-uploaded the photo as the link doesn't work for embeding unless it's in your cache.

(http://www3.picturepush.com/photo/a/12280946/1024/Picture-Box/highres-panasonic-lumix-fz200-8-1342452955.jpg)

Hillarious though!

Personally I would like to see the following lenses from Canon:

20-35mm f/2.0
35-70mm f/2.0
70-160mm f/2.0

These lenes would all be possible as they are aproximately 2x zooms and would have 82mm filter sizes
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: RGF on February 25, 2013, 03:00:49 PM
Consider the size of 2 or 1.4 zoom lens.  Take the focal length and divide by the aperature.  That is a rough guide as to the size of the front lens.  The exact definite of the F stop is the focal length divided by the size of the aperture.  So for a 70-200 F2 lens, the aperture would need to be 100 mm - take this to be the size of the front element.  82 mm filters are expensive enough, 100mm filters would be mucho $$

Well my $0.02 and the limit of knowledge (probably directionally correct but only approximately correct) of optics.
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: rs on February 25, 2013, 03:34:06 PM
I resized and re-uploaded the photo
Thanks
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: qwerty on February 25, 2013, 04:13:59 PM
Has anyone tried actually searching for patents / designs for zoom lenses that are faster than f/2.8 35mm equivalent so that we could get a realistic idea of the size and/or cost?  Surely someone out there has made such a design.

I spend about 30 seconds checking patents for fast zooms, but didn't want to waste the time searching for the crop factor when someone else out there can probably do a better and faster job than I could.

For what its worth, I would probably only pay $2000-2500 for a 35-85mm f/2 that weighed a little over 2 lbs and was comparable to their 24-xxx zooms in image quality (the 24-70 ii is about $2050 currently on amazon).  My wild and speculative guess is that if Canon were to actually introduce such a lens it would be more than double that price, so its kind of a moot point for me.  I would still be interested in seeing design info though.
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: rs on February 25, 2013, 05:47:49 PM
Has anyone tried actually searching for patents / designs for zoom lenses that are faster than f/2.8 35mm equivalent so that we could get a realistic idea of the size and/or cost?  Surely someone out there has made such a design.
Here you go: http://www.adorama.com/HSHC50110.html (http://www.adorama.com/HSHC50110.html)

Hasselblad MF lens 50-110/3.5-4.5, designed for a 44x33mm sensor (0.76x crop). In 35mm speak, its equivalent of a 38-84/2.66-3.42

$5,595, 1.6kgs, 152x103mm, 95mm filters.
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: Hillsilly on February 25, 2013, 08:47:13 PM
Pentax 67 55-100mm F/4.5.  Works out to be a 35mm equivalent f/2.2 zoom.  There would be a few more floating around in medium format land.
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: preppyak on February 28, 2013, 12:56:04 PM
For what its worth, I would probably only pay $2000-2500 for a 35-85mm f/2 that weighed a little over 2 lbs and was comparable to their 24-xxx zooms in image quality (the 24-70 ii is about $2050 currently on amazon).  My wild and speculative guess is that if Canon were to actually introduce such a lens it would be more than double that price, so its kind of a moot point for me.  I would still be interested in seeing design info though.
Yeah, I don't think its a technical limitation, it's more an R&D time limitation that keeps them from making f/2 zooms. As others have mentioned, you'd need a lot of glass and large filters, which by weight and filter size eliminates a lot of the market. Then you have to recoup the cost of R&D, and the cost of all that glass, so your starting point price is already higher than $2500+ I'd bet. Then, because its expensive, fewer people are in the market. Forum kings will complain they can have a 35L, 50L, and 85L for the price, and they are all faster than f/2! So your market grows smaller, and cost goes up. Assume it's a $4000 zoom; who is really buying it over the 24-70 f/2.8 at half the price? Those that NEED f/2 also probably NEED f/1.4 as well.

It's also looking to solve a problem that basically doesn't exist, and that pros likely won't pay for. They'll carry a 35L and an 85L, or a 24-70 and a prime instead. Whereas, with the 200-400, getting a 200-560 zoom that is super high quality and doesn't necessitate lens changes in bad environments is something a pro will pay for. If twice as many paid for it, the lens might cost $8-9000, instead of $11,000+.
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: Hillsilly on April 18, 2013, 05:37:39 AM
Sigma have announced a new 18-35mm F/1.8 zoom lens.  It's for APS-C sensors, but it shows some manufacturers see a market for fast zooms. 
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: bycostello on April 18, 2013, 06:01:53 AM
price
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: Malte_P on April 18, 2013, 06:27:23 AM
they are.. from now on.  ;)
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: infared on April 18, 2013, 06:44:52 AM
There are now:
http://www.dpreview.com/news/2013/04/18/Sigma-announces-worlds-first-F1-8-constant-aperture-zoom-lens (http://www.dpreview.com/news/2013/04/18/Sigma-announces-worlds-first-F1-8-constant-aperture-zoom-lens)
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: woollybear on April 18, 2013, 06:45:33 AM
It is quite easy actually. If you want to know what size it would require just divide the focal length with the required f-stop and you'll see what size the front element diameter would be. So, for a 100-400mm f/1.2 the front element would be 33,3cm in diameter.  :D

If you divide the focal length with the diameter of the front element you'll get the maximum f-stop for that lens.

33,3 cm...wow!!! 
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: Malte_P on April 18, 2013, 07:30:30 AM
It is quite easy actually. If you want to know what size it would require just divide the focal length with the required f-stop and you'll see what size the front element diameter would be. So, for a 100-400mm f/1.2 the front element would be 33,3cm in diameter.  :D

If you divide the focal length with the diameter of the front element you'll get the maximum f-stop for that lens.

33,3 cm...wow!!!

i don´t quite get the math....  8)

can you show how f1.2 gives 33,33 cm on a 100-400mm lens?

it´s more like 83mm for the 100mm end.

by the way:

Quote
The number for lens f/stop in photography (for example, f/8) is the ratio of lens focal length divided by the effective lens aperture. Aperture is not the obvious physical diameter, but instead is the apparent "working" diameter as seen through the magnification of the front lens element.
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: danski0224 on April 18, 2013, 07:48:52 AM
There are now:
http://www.dpreview.com/news/2013/04/18/Sigma-announces-worlds-first-F1-8-constant-aperture-zoom-lens (http://www.dpreview.com/news/2013/04/18/Sigma-announces-worlds-first-F1-8-constant-aperture-zoom-lens)

If that was 16-35 or 12-24 for a full frame sensor....
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: rs on April 18, 2013, 08:13:08 AM
There are now:
http://www.dpreview.com/news/2013/04/18/Sigma-announces-worlds-first-F1-8-constant-aperture-zoom-lens (http://www.dpreview.com/news/2013/04/18/Sigma-announces-worlds-first-F1-8-constant-aperture-zoom-lens)
Equivalent of f2.7 FF on a Nikon 1.5x crop, or f2.9 FF on a Canon 1.6x crop. So on Nikon it is faster than an equivalent of f2.8 FF, but not by much. I'd still prefer a Canon 24-70 II on FF, even if it is 'only' f2.8
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: neuroanatomist on April 18, 2013, 08:20:38 AM
It is quite easy actually. If you want to know what size it would require just divide the focal length with the required f-stop and you'll see what size the front element diameter would be. So, for a 100-400mm f/1.2 the front element would be 33,3cm in diameter.  :D

If you divide the focal length with the diameter of the front element you'll get the maximum f-stop for that lens.

33,3 cm...wow!!!

i don´t quite get the math....  8)

can you show how f1.2 gives 33,33 cm on a 100-400mm lens?

it´s more like 83mm for the 100mm end.

A 100-400mm f/1.2 lens (which will never exist) would need to have a 333.3 mm (13") front element - a practical impossibility.  Your comment about needing an 83mm front element for the 100mm end isn't relevant - the front element can't change size so the optics must be sized for the long end.  That's why the 100-400mm lens is a variable aperture zoom with an f/5.6 long end - if it was f/4.5 throught the zoom range, it would need an 89mm front element.

by the way:

Quote
The number for lens f/stop in photography (for example, f/8) is the ratio of lens focal length divided by the effective lens aperture. Aperture is not the obvious physical diameter, but instead is the apparent "working" diameter as seen through the magnification of the front lens element.

While the above is true, it actually depends on the design of the lens (Roger Cicala has an article on lens designs (http://www.canonrumors.com/tech-articles/lens-genealogy/) that's worth a read).  With a telephoto design, the 'apparent working diameter' or 'virtual aperture' of the lens actually sits right at or just behind the front element.

Put another way, the front element generally needs to be at least as large as (focal length ÷ f/number), and with many lens designs the front element is significantly larger than that. 
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: Malte_P on April 18, 2013, 08:23:57 AM
Quote
A 100-400mm f/1.2 lens (which will never exist) would need to have a 333.3 mm (13") front element - a practical impossibility.  Your comment about needing an 83mm front element for the 100mm end isn't relevant - the front element can't change size so the optics must be sized for the long end.  That's why the 100-400mm lens is a variable aperture zoom with an f/5.6 long end - if it was f/4.5 throught the zoom range, it would need an 89mm front element.

so what he meant is a CONSTANT aperture 100-400mm f1.2?

yeah sorry,  then i was stuck to much in reality...  ;)
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: CamKrist on April 18, 2013, 10:35:14 AM
I sent you in pm
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: RGF on April 18, 2013, 02:06:44 PM
every time you add a stop, the size of the lens more than doubles - 70-200 F4 to 70-200 F2.8.  imagine the size of 70-200 F2.0, it would weigh 5-6 pounds.  And since L lenses cost more than $1000/lb, this monster would be close to $10,000 (USD). Still interested?  I am not.
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: dolina on April 18, 2013, 02:29:35 PM
Weight, technology, materials and price.

The trend today have bodies increasing ISO so the need for faster glass lessens.
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: jrista on April 18, 2013, 02:53:19 PM
Weight, technology, materials and price.

The trend today have bodies increasing ISO so the need for faster glass lessens.

The need is not always for "faster". Sometimes the need is for thinner DOF, which you can only get with a wider aperture.

The fact is, it IS more difficult to develop high quality lenses that perform well at apertures wider than f/2.8. The wider you go, the harder it is to control optical aberrations...and controlling them means more glass, glass with more precise characteristics, and often higher grade materials (high end optical glass, aspheric elements, fluorite or DO elements, etc.) Throw in "zoom", and those issues become even harder to control, as you have to control them such that they balance out at all of the key focal lengths along the zoom range.

I don't think there really is a trend towards lenses with slower apertures. I think f/3.5-5.6 and f/4.5-5.6 lenses, and even at times f/5.6-6.3 lenses, have been used in consumer-grade lenses for decades, by both brand names as well as off-brands. I don't think there are generally more of them now that we have cleaner higher ISO than there was before. I think they just become a little more relevant now that we have clean higher ISO...they are more useful in a broader range of use cases than they were before.
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: noisejammer on April 18, 2013, 03:19:26 PM
To get an idea on the weight - I'll make a wild assumption and say we scale the optical formula. This doesn't really work in practice... whatever :D

Say you go from f/2.8 to f/2. Achieving this means the aperture has to increase by 41.4%. Keeping the same slope on the glass means the glass means the thickness increases by 41.4% too. The result is that the weight of the glass must increase by 1.414^3 = 2.83x.

The structure that supports each lens has to be stiffer, and since it's going to be bigger, the mechanical bits get a lot heavier.

but that's not all....
Optical glass increases in price at roughly the fourth power of the aperture. This means the cost of glass has increased by 4x. Similarly, faster lenses demand tighter tolerances so the manufacturing costs increase. Say this quadruples too.

Suddenly a 70-200 weighs at least 10 lbs and material / manufacture costs $8000.

The price is very high, so the market size is now about 1/100 of the market size for the f/2.8 model. Amortise the development cost makes the lens even more expensive... say $10k.

If you think the numbers are wild, take a look at the Sigma 200-500 / 2.8. $26k and 35 lbs. Compare this with the 120-400/4.5-6. 10x as heavy and 26x more expensive.

Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: TW on April 18, 2013, 04:09:22 PM
Well, as of today, they are! Way to go Sigma. Again!
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: Sporgon on April 18, 2013, 04:22:40 PM
Reading these last few posts reminds me of how surprised I am that my 135/2 isn't larger, especially compared with my 200/2.8
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: infared on April 18, 2013, 04:47:28 PM
There are now:
http://www.dpreview.com/news/2013/04/18/Sigma-announces-worlds-first-F1-8-constant-aperture-zoom-lens (http://www.dpreview.com/news/2013/04/18/Sigma-announces-worlds-first-F1-8-constant-aperture-zoom-lens)
Equivalent of f2.7 FF on a Nikon 1.5x crop, or f2.9 FF on a Canon 1.6x crop. So on Nikon it is faster than an equivalent of f2.8 FF, but not by much. I'd still prefer a Canon 24-70 II on FF, even if it is 'only' f2.8

Agreed...I only shoot FF and MFT...but it is great to see Sigma pushing the envelope.....and if it has great IQ it will be an incredible lens for crop sensor cameras!
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: jcns on April 18, 2013, 05:24:55 PM
200-500 2.8
simply
http://gizmodo.com/5217989/the-photographer-king-needs-no-tripod (http://gizmodo.com/5217989/the-photographer-king-needs-no-tripod)
and only 35lbs.
you want 1.8 with that?
you want IS with that?
have you been curling 45 lb dumbbells?
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: neuroanatomist on April 18, 2013, 06:04:49 PM
Reading these last few posts reminds me of how surprised I am that my 135/2 isn't larger, especially compared with my 200/2.8

135 / 2.0 = 67.5
200 / 2.8 = 71.4

Only 4mm different...
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: woollybear on April 18, 2013, 06:43:26 PM
Reading these last few posts reminds me of how surprised I am that my 135/2 isn't larger, especially compared with my 200/2.8

135 / 2.0 = 67.5
200 / 2.8 = 71.4

Only 4mm different...

Is that different than 67,5 and 71,4?
Easy now....just adding a little humour.
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: RLPhoto on April 18, 2013, 10:02:43 PM
Muhahaha, If this is possible, I believe uber-fast zooms are possible.

http://www.43rumors.com/the-need-for-speed-zoomatar-75mm-180mm-and-250mm-all-f1-3/ (http://www.43rumors.com/the-need-for-speed-zoomatar-75mm-180mm-and-250mm-all-f1-3/)
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: Sporgon on April 19, 2013, 02:13:54 AM
Reading these last few posts reminds me of how surprised I am that my 135/2 isn't larger, especially compared with my 200/2.8

135 / 2.0 = 67.5
200 / 2.8 = 71.4

Only 4mm different...

Yes now you mention it I can see that based on the same maths the 200/2 and the 300/2.8 are similar diameter.

But if the formula is as simple as focal length / f stop, why does my 135/2 vignette much more at f2 than my 200/2.8 does at 2.8 ?
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: K3nt on April 19, 2013, 05:27:22 AM
Reading these last few posts reminds me of how surprised I am that my 135/2 isn't larger, especially compared with my 200/2.8

135 / 2.0 = 67.5
200 / 2.8 = 71.4

Only 4mm different...

Yes now you mention it I can see that based on the same maths the 200/2 and the 300/2.8 are similar diameter.

But if the formula is as simple as focal length / f stop, why does my 135/2 vignette much more at f2 than my 200/2.8 does at 2.8 ?

The simple formula is just that.. simple and a guideline. A lot more goes on in the world that is precision optics that can produce(or not) the vignetting you're experiencing.
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: Sporgon on April 19, 2013, 07:12:46 AM
Reading these last few posts reminds me of how surprised I am that my 135/2 isn't larger, especially compared with my 200/2.8

135 / 2.0 = 67.5
200 / 2.8 = 71.4

Only 4mm different...

Yes now you mention it I can see that based on the same maths the 200/2 and the 300/2.8 are similar diameter.

But if the formula is as simple as focal length / f stop, why does my 135/2 vignette much more at f2 than my 200/2.8 does at 2.8 ?

The simple formula is just that.. simple and a guideline. A lot more goes on in the world that is precision optics that can produce(or not) the vignetting you're experiencing.


My questiion is essentially, what goes on ?

So to reply 'a lot more goes on' is hardly an answer.

I suspect it has to do with the physics of passing light through a group of lenses: the closer the design comes to perfect 100% transmission of the light value the more disproportionate the fall off at the extreme of the image circle.  So to avoid more vignetting the faster lenses would have to produce a larger image circle, which would increase size, weight and cost in a similar vein to the OP's original question on zooms.

So given that the 135/2 and 200/2.8 are of a similar design and price, I should have expected the faster lens to have more vignetting when wide open.
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: ksagomonyants on April 19, 2013, 08:33:49 AM
http://www.canonrumors.com/2013/04/sigma-announces-18-35-f1-8-dc-hsm-art-for-aps-c/ (http://www.canonrumors.com/2013/04/sigma-announces-18-35-f1-8-dc-hsm-art-for-aps-c/)
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: Lawliet on April 20, 2013, 10:07:11 AM

But if the formula is as simple as focal length / f stop, why does my 135/2 vignette much more at f2 than my 200/2.8 does at 2.8 ?
Basically: The lenses have the same diameter, but at longer focal lengths they need less curvature.  The latter is the cause of most flaws in a lens. More a problem with wide angle lenses would be the cos^4-law, i.e. the kind of vignetting that comes from rays hitting the aperture from far off the optical axis. Think of a disc, if you look at it from lets say 45° it looks like a cats eye, less area to get light through then the full circle (or just look at bokeh-discs, round in the center, recompose and they get squashed)
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: jrista on April 20, 2013, 11:24:15 AM
Muhahaha, If this is possible, I believe uber-fast zooms are possible.

http://www.43rumors.com/the-need-for-speed-zoomatar-75mm-180mm-and-250mm-all-f1-3/ (http://www.43rumors.com/the-need-for-speed-zoomatar-75mm-180mm-and-250mm-all-f1-3/)

Hah! That is one crazy lens! I wonder what the IQ was like wide open...that thing must have had some beastly CA!
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: jrista on April 20, 2013, 11:37:04 AM
Reading these last few posts reminds me of how surprised I am that my 135/2 isn't larger, especially compared with my 200/2.8

135 / 2.0 = 67.5
200 / 2.8 = 71.4

Only 4mm different...

Yes now you mention it I can see that based on the same maths the 200/2 and the 300/2.8 are similar diameter.

But if the formula is as simple as focal length / f stop, why does my 135/2 vignette much more at f2 than my 200/2.8 does at 2.8 ?

The simple formula is just that.. simple and a guideline. A lot more goes on in the world that is precision optics that can produce(or not) the vignetting you're experiencing.

Just to be specific, the relative aperture as a ratio couldn't be called a "guideline". It is a mathematical fact. The "entrance pupil" diameter, which is the diameter of the aperture as viewed through the front of the lens at "infinity distance", quite literally IS the focal length divided by the relative aperture number. There is no guideline here, that is quite specifically EXACTLY how to compute the size of the entrance pupil, which puts a limit on the minimum size the front element can possibly be. If the front element were smaller than that, then the entrance pupil would have to be smaller as well.

Sometimes manufacturers "fudge" the design a little. For example, the 100-400mm L lens is actually more like 390mm, and the entrance pupil and the diameter of the front element are just a little smaller than would actually be necessary for a lens that was truly 400mm long (I've actually measured it myself.) For a ~390mm focal length, the numbers add up and seem to be correct, probably because it was a matter of manufacturability vs. cost to shorten the lens just a little. Not that it matters much, a few mm difference in focal length aren't going to matter (less than 5% difference in subject size relative to the frame), but it could mean quite a bit from a cost standpoint.

The size of the front element of a lens cannot be smaller than the entrance pupil, however it can be larger. I guess you could say it is a "guideline" that the front element has to be at least as large as the entrance pupil. Wide angle lenses tend to have front elements that are significantly larger than their entrance pupils, less so because of the needed light gathering power and more so just so they can gather incident light from an appropriately wide angle. In my 16-35mm f/2.8 L lens, for example, the front element is HUGE, while the aperture is quite tiny in comparison. I'd say the front element is dozens of times larger in area than the entrance pupil, maybe a dozen times larger in diameter.
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: K3nt on April 22, 2013, 02:48:30 AM
Reading these last few posts reminds me of how surprised I am that my 135/2 isn't larger, especially compared with my 200/2.8

135 / 2.0 = 67.5
200 / 2.8 = 71.4

Only 4mm different...

Yes now you mention it I can see that based on the same maths the 200/2 and the 300/2.8 are similar diameter.

But if the formula is as simple as focal length / f stop, why does my 135/2 vignette much more at f2 than my 200/2.8 does at 2.8 ?

The simple formula is just that.. simple and a guideline. A lot more goes on in the world that is precision optics that can produce(or not) the vignetting you're experiencing.

Just to be specific, the relative aperture as a ratio couldn't be called a "guideline". It is a mathematical fact. The "entrance pupil" diameter, which is the diameter of the aperture as viewed through the front of the lens at "infinity distance", quite literally IS the focal length divided by the relative aperture number. There is no guideline here, that is quite specifically EXACTLY how to compute the size of the entrance pupil, which puts a limit on the minimum size the front element can possibly be. If the front element were smaller than that, then the entrance pupil would have to be smaller as well.

Sometimes manufacturers "fudge" the design a little. For example, the 100-400mm L lens is actually more like 390mm, and the entrance pupil and the diameter of the front element are just a little smaller than would actually be necessary for a lens that was truly 400mm long (I've actually measured it myself.) For a ~390mm focal length, the numbers add up and seem to be correct, probably because it was a matter of manufacturability vs. cost to shorten the lens just a little. Not that it matters much, a few mm difference in focal length aren't going to matter (less than 5% difference in subject size relative to the frame), but it could mean quite a bit from a cost standpoint.

The size of the front element of a lens cannot be smaller than the entrance pupil, however it can be larger. I guess you could say it is a "guideline" that the front element has to be at least as large as the entrance pupil. Wide angle lenses tend to have front elements that are significantly larger than their entrance pupils, less so because of the needed light gathering power and more so just so they can gather incident light from an appropriately wide angle. In my 16-35mm f/2.8 L lens, for example, the front element is HUGE, while the aperture is quite tiny in comparison. I'd say the front element is dozens of times larger in area than the entrance pupil, maybe a dozen times larger in diameter.

I know the f-stop and focal length formula is definite. What I was referring to is the magic that happens beyond that. Compensating for CA, flare, coatings, lens material they all contribute to the final resulting light that eventually ends up saturating the sensor behind the lens. And yes, like you say, some lenses are using a lot larger front elements that would, based on the maths alone, be overkill.

I enjoy this thread. Excellent stuff in here and good discussion. Have a great week all of you!  ;D
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: Einstein333 on April 22, 2013, 03:52:34 AM
I wish they would make a really fast standard zoom lens like a 30-90 f2.0 OS...
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: wickidwombat on April 22, 2013, 07:10:30 PM
I wish they would make a really fast standard zoom lens like a 30-90 f2.0 OS...

oh yeah I have been wishing a 35-85 f2 with IS would come out (for full frame not friggin crop!) for such a long time hopefully the narrower zoom range would allow more control over distortion and other imperfections than 30-90 which i think would be more compromised.
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: RGF on April 22, 2013, 07:46:08 PM
I wish they would make a really fast standard zoom lens like a 30-90 f2.0 OS...

oh yeah I have been wishing a 35-85 f2 with IS would come out (for full frame not friggin crop!) for such a long time hopefully the narrower zoom range would allow more control over distortion and other imperfections than 30-90 which i think would be more compromised.

Would you pay $5000 for such a lens?  Would you be willing to carry a 5 Lb lens with you?

I don't think there is a market for such a lens
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: tiger82 on April 22, 2013, 09:05:25 PM
Check out the price, size, and weight of the Sigma 200-500 f/2.8
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: wickidwombat on April 22, 2013, 09:12:03 PM
I wish they would make a really fast standard zoom lens like a 30-90 f2.0 OS...

oh yeah I have been wishing a 35-85 f2 with IS would come out (for full frame not friggin crop!) for such a long time hopefully the narrower zoom range would allow more control over distortion and other imperfections than 30-90 which i think would be more compromised.
absolutly yes to both however i dont think it would be 5lbs I might be fatter than the 70-200 with maybe an 82mm filter but not as long and perhaps a similar weight
Would you pay $5000 for such a lens?  Would you be willing to carry a 5 Lb lens with you?

I don't think there is a market for such a lens
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: psolberg on April 23, 2013, 03:33:01 PM
sigma makes a 1.8 zoom for APS-C. For full frame, you're just dreaming.
Title: Re: Why aren't zoom lenses faster than 2.8?
Post by: SambalOelek on April 24, 2013, 06:11:29 AM
It's definitely possible to make a practical <2.8 zoom lens with a conservative zoom range (not too wide and not too long).

The Tokina AF 28-70mm f/2.6-2.8 AT-X Pro II is a (discontinued) full-frame lens that is a tad faster than 2.8 at the wide-end, and it's not very large (A bit larger than the 24-105 f/4 IS). Moreover it's fixed length (does not extend while zooming). Quite a nice piece of engineering.