Plausibility of a 100-400mm f/4 L IS USM?

[jrista]

I'm a big fan of my 100-400mm f/4.5-5.6 L IS USM lens. Its served me quite well, and better than the 400mm f/5.6 lenses I've tried from friends or other fellow photographers met out in the field. The only real detractor, however, is the aperture range...f/4.5 to f/5.6 is a bit limiting, from an AF standpoint, and from the standpoint of using a teleconverter. I'd love to have a relatively affordable telephoto zoom lens that I could slap a 1.4x TC on to get 140-560mm f/5.6, something cheaper than the new 200-400mm f/4 L IS USM.

Is a 100-400m f/4 a plausibility, for a "reasonable" cost around $3500 or so? Would it be a lens anyone else even cared about, or is that just a focal range and price that doesn't serve anyone's needs? Personally, I'd find 560/5.6 to be far more useful for general bird photography, without having to lug around a heavy 500mm or 600m L.

Thoughts?

[Fleetie]

So you're asking for a lens with twice the zoom ratio of the 200-400L at the same aperture, for a lower price?

Ok, I seem to remember the 200-400L is the one with a built-in 1.4x teleconverter, isn't it?

But apart from the lack of that built in*, why would your proposed lens be much cheaper?

Maybe you're suggesting that you'd live with slightly lower IQ in your lens, to reduce cost?

Unfortunately, both lenses are 400 f/4 at the long end, so both need at least a 100mm front element, and similar barrel sizes, so not much potential for cost saving there, I'd have thought.

And a 4x zoom ratio is asking a lot if you want good IQ throughout - which is going to cost a lot.

(I might be thinking of the wrong lens when I'm talking about the 200-400 with 1.4 built in, though....)


* But you've said you need this 1.4x converter anyway so there's another £450 you'd have to spend on that, too, which for your requirements detracts from any cost advantage of your proposed lens even further.

[lol]

Never mind the zoom part, a 400mm f/4 is 400mm f/4 regardless, and not going to be cheap. Especially with the upcoming availability of the 200-400/4 I doubt they'll do another zoom that close in the ball park.

I think the nearest affordable option is the Sigma 120-300/2.8 OS which seems great value for money. I'd love Canon to do their own one too, but you know it wont be so affordable any more!

[smirkypants]

The excellent Nikon 200-400/f4 costs about $7000 street and weighs twice what the 100-400 weighs. Adding another 100mm on the short end would significantly increase the weigh and price. Sorry to burst your bubble, but I'm afraid you are asking for too much.

[KeithR]

Is a 100-400m f/4 a plausibility, for a "reasonable" cost around $3500 or so?

If you do what I did - buy a Sigma 120-300mm f/2.8 OS and slap a 1.4x on it...

[Cosk]

both lenses are 400 f/4 at the long end, so both need at least a 100mm front element

Just to build on that... aperture diameter is focal length / f*stop, and the front element has to be at least as large as the aperture... usually more. 

So a 400mm f/4 requires a 100mm aperture...
a 400mm f/5.6 is 72mm

Physically, each stop (f4>5.6) requires 2x the surface area of glass of every element.
Generally, each stop means ~2x the weight and ~2x the cost.

So, assuming similar build and quality, features, and nothing fancy like Diffractive Optics, a 100-400 f/4 will be in the same ballpark from a weight and cost standpoint as 200-400 f/4 or a 300-400 f/4.

Personally, I'd love to see an anything-400 f/5.6 that's less than half the weight and less than half the cost as the 200-400 f/4... with the latest generation of IS, a twist zoom, and compacts to the length of the 70-300L (and those specs are physically possible to achieve). 

[jrista]

Well, I guess I figured the integrated 1.4x TC added a fair bit to the cost, but perhaps not. I'm also not sure I believe the difference between a 71.4mm aperture (400/5.6) and a 100mm aperture would literally cost thousands of dollars for the front element...were talking a difference of roughly 28mm in size. I'm sure it adds to the cost, but if we take the current 100-400 f/4.5-5.6 which runs about $1800, to the 200-400 f/4 which is supposed to run around $7000...were talking a $5200 difference in price. I don't think the entire difference is allocated to glass...there is the integrated TC, R&D costs to design the thing that need to be recouped, etc.

A normal 1.4x TC costs some $500, and if we assume the built-in TC for the 200-400 is explicitly tuned for that particular lens, it probably cost more than that. Knock off $800-$1000 of the price of the 200-400 for the integrated TC, and we have a price difference of around $4300. I would NOT necessarily expect the kind of IQ from the 200-400 out of a 100-400...I'd expect it to be about as good as or maybe slightly better than the current 100-400, and there wouldn't be an integrated TC.

So, perhaps $3500 is overly hopeful...lets say $4500? Is that any more reasonable, assuming current 100-400 f/4.5-5.6 IQ, with a modern IS system? I'll certainly add that the short end really doesn't matter a wit to me...it could be 200-400, or even 250-400, if that would make it cheaper, as I rarely ever use the 100-200mm range on my current one, as I mostly photograph birds and wildlife with it.

Again, I'm just probing the pluasibility of such a lens, and currently, it seems particularly implausible at around $3500...

[jrista]

Is a 100-400m f/4 a plausibility, for a "reasonable" cost around $3500 or so?

If you do what I did - buy a Sigma 120-300mm f/2.8 OS and slap a 1.4x on it...

The sigma+1.4xTC would only get me 420 on the long end. It would get me 600mm on the long end with a 2x TC, but I'm curious how much that would affect IQ...more than I'd care for, I think. I want 560 on the long end, and I would gladly take 200 or 250 on the short end without any TC, as I don't really shoot shorter than that anyway.

[jrista]

both lenses are 400 f/4 at the long end, so both need at least a 100mm front element

Just to build on that... aperture diameter is focal length / f*stop, and the front element has to be at least as large as the aperture... usually more. 

Technically speaking, the aperture is the entrance pupil (physical aperture as viewed through the front element)...so the front element has to be large enough to make the aperture appear to be 100mm. Physically, the aperture would be much smaller, given the magnification factor from the diaphragm to the front element. I'm not really sure how that translates into front element surface area though...

So a 400mm f/4 requires a 100mm aperture...
a 400mm f/5.6 is 72mm

Physically, each stop (f4>5.6) requires 2x the surface area of glass of every element.
Generally, each stop means ~2x the weight and ~2x the cost.

I know it would require roughly that much more surface area for the front element...but I'm skeptical it would need that much for every element...the point is to magnify the entrance pupil to appear to be 100mm when observed through the front of the lens, not actually make the physical diameter of the aperture 100mm.

So, assuming similar build and quality, features, and nothing fancy like Diffractive Optics, a 100-400 f/4 will be in the same ballpark from a weight and cost standpoint as 200-400 f/4 or a 300-400 f/4.

Personally, I'd love to see an anything-400 f/5.6 that's less than half the weight and less than half the cost as the 200-400 f/4... with the latest generation of IS, a twist zoom, and compacts to the length of the 70-300L (and those specs are physically possible to achieve).

Totally agreed, I don't actually need 100mm on the short end. I could do with 200, even 250mm, without a built-in TC. The desire is to have a lens that can go from 400mm on the long end to 560mm on the long end with a 1.4x TC, improving its versatility without pushing cost beyond reach. Its too bad all of Canon's pro bodies, including the 7D, don't support AF at f/8. I'd gladly take a 250-400 f/5.6 w/o integrated TC, slap on a 1.4x, and use it from 350-560 f/8 for birding...if it cost around $3500-$4000.

[KeithR]

It would get me 600mm on the long end with a 2x TC, but I'm curious how much that would affect IQ...more than I'd care for, I think.

That's not what I'm finding.

What I'm seeing is more like this and this.

[jwong]

Is a 100-400m f/4 a plausibility, for a "reasonable" cost around $3500 or so? Would it be a lens anyone else even cared about, or is that just a focal range and price that doesn't serve anyone's needs? Personally, I'd find 560/5.6 to be far more useful for general bird photography, without having to lug around a heavy 500mm or 600m L.

Thoughts?

I don't think that it's possible for 3.5k.  For larger lenses, weight does tend to double for 1 stop increase in speed.  For example, the 200mm f/2.8 is 27 oz while the 70-200II f/2.8 is 52 oz and the 200mm f/2.0 is 91 oz.  At 300mm, the f/4 weighs 42 oz and the f/2.8 weighs 83 oz.  Therefore, it wouldn't be unexpected that a f/4 zoom to 400 would weigh roughly twice the weight of the 100-400 f/4.5-5.6.  Given that the existing 100-400 weighs 48 oz, it would be surprising that the f/4 zoom weigh close to 100 oz.  The 300mm f/2.8 weighs 83 oz, which would be lighter than a 100-400mm f/4 zoom, and that thing already $7300.  So, I'd have to agree with others that it would not be possible to build it for 3.5k.

[jasonsim]

No way they will make a 100-400mm f4L IS lens.  No reason for them to since the 200-400 f/4L with 1.4x is on the way.

They should make a version II of the 100-400mm f/4.5-5.6L IS USM: give it latest IS, and twist zoom, and latest flourite coatings.

They should also think about coming out with a new 400mm f/4L...the one with DO is...well...outdated and the 400mm f/5.6L has no IS.  Not everyone wants a 400mm f/2.8L beast to lug around.

[lol]

Technically speaking, the aperture is the entrance pupil (physical aperture as viewed through the front element)...so the front element has to be large enough to make the aperture appear to be 100mm. Physically, the aperture would be much smaller, given the magnification factor from the diaphragm to the front element. I'm not really sure how that translates into front element surface area though...

For longer focal lengths as discussed in this thread, you can take it as given the lens front size is same as the entrance pupil. You only tend to see a smaller entrance pupil than the lens front for wide angles.

[Mt Spokane Photography]

The 100-400mm when upgraded will sell for over $3000, a f/4 version about $7500, maybe more.  Just chack the price of a 400mm f/4 DO right now, and imagine a lot more.

[jrista]

Technically speaking, the aperture is the entrance pupil (physical aperture as viewed through the front element)...so the front element has to be large enough to make the aperture appear to be 100mm. Physically, the aperture would be much smaller, given the magnification factor from the diaphragm to the front element. I'm not really sure how that translates into front element surface area though...

For longer focal lengths as discussed in this thread, you can take it as given the lens front size is same as the entrance pupil. You only tend to see a smaller entrance pupil than the lens front for wide angles.

Sorry, but its physically impossible for the entrance pupil to be exactly as large as the front element...your looking down a tube, your going to see the first half of the tube that leads up to the diaphragm regardless, so that guarantees the entrance pupil is smaller than the front element. For a visual example of how large the entire diaphragm is compared to the front element, take a look at this image from Canon's patent on the unreleased EF 100-400mm f/4-5.6 L: http://egami.blog.so-net.ne.jp/_images/blog/_f82/egami/2011_215218_fig04-9b046.png. The diaphragm and aperture are smaller than the first three elements.

My point was not that the front lens element would be smaller than the entrance pupil...it has to be BIGGER! Otherwise you can't magnify the aperture to appear as large as it would need to be. Anyway, my point was, its not a gargantuan difference between an f/5.6 aperture and an f/4...not like a move to f/2.8 would be (in which case, yes, I'd expect the lens to be monstrously HUGE and extremely expensive...something along the lines of Sigma's Bigma.)

Anyway, it was wishful thinking to start with, and the simple fact is that Canon is already releasing a 200-400 f/4 L w/ 1.4x TC. I'll just have to wait for that sucker to go on a nice sale and pick one of those up, as its essentially what I want, just a couple thousand dollars more than I want to spend. I guess we'll see where street price ends up after a few months on the market.