Messages

46

Third Party Manufacturers / Re: Sigma Announces 18-35 f/1.8 DC HSM Art for APS-C

« on: April 19, 2013, 11:13:28 AM »

...

You are mixing two concepts that are unrelated.

If we talk about framing, then you're right. The smaller effective aperture is the reason why DoF is bigger on crop at a given aperture and angle of view (note that I didn't say focal length).

However, framing has nothing to do with light gathering. f-stops are a function of focal length, not angle of view. A 50mm is a 50mm on every camera. It's the angle of view that changes in relation to sensor size, not the focal length.

Another quote from Wikipedia:

A 100 mm focal length f/4 lens has an entrance pupil diameter of 25 mm. A 200 mm focal length f/4 lens has an entrance pupil diameter of 50 mm. The 200 mm lens's entrance pupil is larger than that of the 100 mm lens, but given the same light transmission efficiency, both will produce the same illuminance at the focal plane when imaging a scene of a given luminance.

But to compare a crop lens, crop sensor combo to a FF lens, FF sensor combo, there's no point in comparing two with different framing - otherwise you'd be arguing this 18-35 crop lens is a direct equivalent of a 16-35 FF lens on FF.

You can compare what you want, as long as you it correctly. The way you do it is the way you can compare angles of view. This is fine as long as you don't make the mistake to consider angle of view = focal length and to put this value into a f/stop calculation.

To exaggerate, is a 100mm f5.6 large format lens with its huge image circle the same as a 100mm f5.6 lens and its tiny image circle on a compact? Is it wrong to compare lenses which give the same framing? Surely from a photographers point of view, they're two very different lenses?

Focal length is what it is. You can mount an old Zeiss for Hasselblad lens on your Canon camera and the focal length will not change. It would give you the same framing of a 100mm Canon lens.

Wikipedia doesn't take into account imaging circle in that equation you're quoting. The aperture of a lens is a bit like working out the speed of water in a hose pipe. The imaging circle is a bit like the diameter of the pipe. Widen the pipe and keep the speed the same, you get more coming through.

More flow, but not more pressure. Same with light: you get more light coming in in total, but the amount of light / surface of the sensor would be the same. Any extra light that comes in will not affect exposure.

Or think about it like this - imagine a photo taken with a FF lens and a FF sensor. Now you take that same photo and you crop out just the centre 40% - you've taken away 60% of the image - which is also 60% of the light that passed through that FF lens. You're left with only 40% of the light. That's what crop does. You need a faster lens on crop to make it capture the same amount of light in that smaller area.

Same as above. A smaller sensor is actually a smaller mouth to feed. This is why you can have compact cameras with 1" sensor and f/1.8 lenses.

47

Third Party Manufacturers / Re: Sigma Announces 18-35 f/1.8 DC HSM Art for APS-C

« on: April 19, 2013, 09:23:43 AM »

I think the wheels come off because we are using "full-frame" lenses on "crop-frame" cameras, and insist on comparing everything to the "35mm" (aka "full-frame") format.

This can be done with no problems. The important thing is not to confuse focal length with angle of view. We can say that a 50mm gives you the same framing ( = angle of view) of a 80mm on FF; however, other parameters related specifically to focal length and not to angle of view are not affected.

48

Third Party Manufacturers / Re: Sigma Announces 18-35 f/1.8 DC HSM Art for APS-C

« on: April 19, 2013, 08:47:52 AM »

...

You are mixing two concepts that are unrelated.

If we talk about framing, then you're right. The smaller effective aperture is the reason why DoF is bigger on crop at a given aperture and angle of view (note that I didn't say focal length).

However, framing has nothing to do with light gathering. f-stops are a function of focal length, not angle of view. A 50mm is a 50mm on every camera. It's the angle of view that changes in relation to sensor size, not the focal length.

Another quote from Wikipedia:

A 100 mm focal length f/4 lens has an entrance pupil diameter of 25 mm. A 200 mm focal length f/4 lens has an entrance pupil diameter of 50 mm. The 200 mm lens's entrance pupil is larger than that of the 100 mm lens, but given the same light transmission efficiency, both will produce the same illuminance at the focal plane when imaging a scene of a given luminance.

49

Third Party Manufacturers / Re: Sigma Announces 18-35 f/1.8 DC HSM Art for APS-C

« on: April 19, 2013, 08:25:25 AM »

Hey guys, read what I wrote. I said f1.8 on crop is brighter than f2.8 on full frame when both have the same shutter speed and ISO, then you start telling me that I'm wrong to say FF is brighter when they're both at f1.8 and the same shutter speed and ISO. I didn't say that, so what gives? I went to great lengths to explain that at the same aperture, shutter speed and ISO, they both expose the same due to the different light gathering of the format being compensated for by the amplifiers being set different. If you can look past that same exposure settings between formats and start to use the higher ISO's with lower noise levels this lower amplification of FF rewards you with, you'll find the true nature of the light gathering of FF lenses on FF sensors.
...

80mm 1.0x [FF]      @ f/2 aperture = 40mm diam pupil
50mm 1.6x [APSC] @ f/2 aperture = 25mm diam pupil

He is not.

In optics, the f-number (sometimes called focal ratio, f-ratio, f-stop, or relative aperture[1]) of an optical system is the ratio of the lens's focal length to the diameter of the entrance pupil.

You can't compare different focal lenghts. A 50mm is a 50mm both on crop and FF. However, being the former smaller, you crop the edges to a degree which would be equivalent to the angle of view of a 80mm on FF. This is a quick way to grasp the concept, but it's not exact in a way that you can make calculations.

50

Third Party Manufacturers / Re: Sigma Announces 18-35 f/1.8 DC HSM Art for APS-C

« on: April 19, 2013, 07:08:15 AM »

Aperture is just a way to measure the diameter of the iris blade. It's connected to, but it doesn't measure, the real amount of light gathered. This is why T-stops were invented.

T-stops are a measured version of light as opposed to f stops which are theoretical - so they take into account the transmission of light, including effects such as reflections and tinting of glass. However, even T-stops don't take into account the size of the imaging circle or the size of the sensor. That's why a 24-70/2.8 II on FF is more than a worthy rival to this 18-35/1.8 on crop, yet if you mount the same 24-70/2.8 II on crop, it is not.

Exactly. F-stops = T-stops in an ideal lens; in practical terms they are a better measure of DoF than they are of light transmission.

I don't agree with the rest though. Or better, I'm not quite sure what you mean.

51

Third Party Manufacturers / Re: Sigma Announces 18-35 f/1.8 DC HSM Art for APS-C

« on: April 19, 2013, 02:32:43 AM »

Surely you know that taking this small sensor, large aperture thing to extremes like this does not result in this Panasonic FZ200 having a lens equivalent of a 600mm f2.8 at full zoom, as Panasonic would like you to think? In terms of framing, yes. In terms of exposure due to ISO tweaking of the sensor, yes. In terms if DoF, no. In terms if light gathering, no! There's no way that a 'slow' Canon 600/4 II on a 1D X as a package gathers less light than that 'f2.8' lens/sensor combo of the Panasonic. Yes, both at f4, 1/1000th of a sec, they'll both have to use an identical ISO to expose the same, but look past using the same rated ISO and guess which combo would work best to get clean images at high shutter speeds in low light?

If you can understand that, then surely you can see the 1.6x crop gives just over a stop less light gathering than a full frame sensor - making f1.8 on crop equal in light capturing terms to an aperture 1.6x smaller on FF - f2.88.

Aperture is just a way to measure the diameter of the iris blade. It's connected to, but it doesn't measure, the real amount of light gathered. This is why T-stops were invented.

52

EOS Bodies / Re: 21mp Sensor in the 7D Mark II? [CR1]

« on: April 19, 2013, 02:29:40 AM »

I know two different prototypes. But no one has a Digic 6 in it.

It´s time that Canon reduces the price of the 5D Mark III around 2000 bucks and put a FF camera between the 5D Mark III and 1D X on the market that is worth the money you pay for it. I need a better IQ in the range ISO 50 to ISO 800.

A price drop in the 5D3 would be most welcome.

However, a new sensor would make the 70D a very interesting proposition.

53

Lenses / Re: Better for head shots, portraits: 100mm f.2.8L Macro IS or 70-200 f.2.8L IS II?

« on: April 18, 2013, 04:00:51 PM »

Definitely better bokeh from the macro.

54

Third Party Manufacturers / Re: Sigma Announces 18-35 f/1.8 DC HSM Art for APS-C

« on: April 18, 2013, 03:57:20 PM »

Some people forget that F aperture is not (just) about bokeh, blur, etc. its about the amount of light which can reach the sensor. In that matter the F value is equivalent between FF and APS-C.

I don't think so. Aperture is about the diameter of the blade iris. The amount of light actually conveyed to the sensor is measured in T stops.

55

Third Party Manufacturers / Re: Sigma Announces 18-35 f/1.8 DC HSM Art for APS-C

« on: April 18, 2013, 11:16:20 AM »

I think what has happened is that Canon's pricing policies have become SO absurd that is has given some astute tech. and money managers at Sigma the ability to realize that they have a lot more wiggle room to make a great product and still be super competitive in price to big read. (it also shows how ridiculous Canon's pricing has become). I do not own a crop body either, but I do LOVE the appearance of this lens! Hope the IQ and price/performance ratio are right up there with the Sigma 35mm, f/1.4 that I own and absolutely love. This can be nothing but good for all of us! Can't wait to see what the next lens is in the new Art Line!!!!!!!

I'm actually tremendously interested in a new version of their 24-70/2.8 and who knows, maybe something like a 24-90/4. The Tamron is quite good, but Sigma looks like they don't want to be a "second choice" anymore. I love when 3rd-party manufacturers deliver such quality; they set you free from this or that system.

This is great for crop shooters.  However, before everyone gets excited over the f/1.8 bit, you have to remember that f/1.8 on a crop sensor is nothing like f/1.8 on a FF sensor.  This lens will give the same angle of view, image noise for given exposure parameters (*1), depth of field at a given AOV and subject distance (*2), etc. etc. etc. as a 28-50mm f/2.8 full frame lens.

In other words, if the lenses and sensors are perfect, this lens on a crop sensor would give identical results to a 28-50mm f/2.8 on a FF sensor.  However, lens and sensor imperfections actually favor the larger format sensor, so don't expect this lens to give anything as good as the 24-70 f/2.8 original or the tamron.

Still, its great improvement for crop shooters (if it keeps up with recent Sigma trends), and should be relatively compact.

(*1) This considers photon shot noise only and assumes photos are rescaled to same resolution when printed.
(*2) At non-macro distances

Depending on the price point, the difference between a FF + 24-70 and DX + 18-35 might be what is truly impressive. This lens is not going to reach anything tremendous from an absolute perspective, but it's going to narrow the gap between crop and FF. Actually, I think it would make for an amazing travel lens since it would eliminate the need of a fast prime. If you want to travel light and bring only a crop body and one lens, you either go for a usual standard zoom and live with the slow aperture or you go with something like this.

56

EOS Bodies - For Stills / Re: What made you choose Canon in the first place?

« on: April 18, 2013, 10:01:21 AM »

My first DSLR was a 500D. Back in the day I was a student and couldn't afford anything too fancy, and I liked the Rebel line better than its Nikon equivalent. I also felt that Canon color rendition was more pleasant - which is different from more accurate, as many like to say. Many of my friends had Canon rebels too, so at that time I trusted their opinion.

57

Third Party Manufacturers / Re: Sigma 18-35 f/1.8 DC?

« on: April 18, 2013, 07:36:57 AM »

Judging from the way other ultra-large-aperture zooms are designed (e.g. the Oly 35-100 f/2) I'd guess that the design is basically a 35-70 f/3.5 with a reversed 2x teleconverter at the back.

I imagine that an FF version of this concept would weigh well north of a kilogram (& cost well north of a kilobuck).

Kudos to Sigma for being innovative once again.  Hopefully this will show C & N that there's real demand for more large-aperture lenses.

I've said this before and I'll say again, do we really mind a 1.4 kg lens that covers 24-70 at f1.8? We carry the 70-200 with that weight with no issues, so why not a 24-70?

I think there would be problems in doing a sharp lens with those features. If you look at the MTF charts for this Sigma it's clear that border performance suffers quite a bit wide open - and it's only a 15 MP APSC.

58

Lenses / Re: Sigma 18-35 F/1.8 just announced?!

« on: April 18, 2013, 05:08:12 AM »

excuse my ignorance.... but why all the world on the net is talking about this lens to be equal to a f2.7 (f2.9) FF lens?

f1.8 is f1.8.... ?

here too:

So it's 18-35 f/1.8 for APS-C, making at a FF-equivalent of 29-56 f/2.9

i mean when i put a 50mm f1.8 on FF or APS-C it´s an f1.8 lens.

In terms of DoF

59

Lenses / Re: Sigma 18-35 F/1.8 just announced?!

« on: April 18, 2013, 04:48:04 AM »

Someone help me understand the market target for such a lens.  After all, I thought the people buying high end glass for their APS-C rigs are 7D users buying long primes for birding.  What APS-C users have been lamenting that their 17-55 F/2.8 IS isn't quick enough?  I would argue that as cool as such a new lens might be to use, this can't be a massive gap in the APS-C users' bag, right?

So so so confused.  Help me make sense of this, thx.

- A

A lot will depend on the price point and actual IQ of course.

I see it as a travel lens. While there are many good standard zooms on APSC, many times I felt like I needed a fast prime too for portraits and subject isolation. This lens kind of fills that gap - please also note the 28cm MFD.

60

Third Party Manufacturers / Re: Sigma 18-35 f/1.8 DC?

« on: April 18, 2013, 04:19:15 AM »

Holy 5h!t ... f/1.8 on a zoom lens? ... if its real, that'd be freakin AWESOME!

It is real, it's been officially announced