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Messages - epsiloneri

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331
EOS Bodies / Re: *UPDATE* 1Ds Mark IV Feature
« on: October 19, 2010, 07:04:01 PM »
This gives them room to improve the 5D line and a *key* feature to differentiate the 1Ds. Pixel binning would be huge is potential advantage for low-light and/or extreme high quality work.

Why is that? The only advantage I see with in-camera binning is size of files/speed (which is nice, but I don't see the huge potential). One might also save some readout noise, but I doubt that's significant in most situations.

332
Lenses / Re: Sigma 85 f/1.4 EX DG Available Soon
« on: October 17, 2010, 05:33:12 AM »
Because all FF lenses perform better on crop bodies which take advantage of the sweet spot

That's true, but the FF optical performance of the sigma is not much in question. Its border resolution is as good or better than the Canon EF 50mm f/1.2 USM L (which itself is not very good in the border resolution department; see photozone.de, or the review by dpreview.com). The problem with the sigma is its AF. And I cannot see how AF issues would be less on a crop body.

For equivalent framing to use of the lens on FF, the depth of field on the crop body would be deeper.  So, f tihere are AF issues, they would be masked on a crop body by the deeper DoF.

Hehe, I think we've covered this topic before. Actually, AF issues get worse, if anything, with crop. I'm not going through the crop vs. FF lens/image equivalence thing again, but will merely give you an example that will make you immediately understand why. Imagine you have a focus error with a FF camera, such that the de-focused resolution is 1/160 of the image width (0.6%). Then the equivalent image in a crop camera, would be to crop that exact FF image with a factor 1.6x. The AF error would now be 1/100 (1%) of the image size - which is clearly worse. Resolution in terms of resolved minimum angle would of course be the same (the crop image is, after all, the central part of the same image as the FF).

333
Lenses / Re: Sigma 85 f/1.4 EX DG Available Soon
« on: October 16, 2010, 12:19:42 PM »
Reasonable in what way?  Fair? here's a quote:
These were not even close-distance shots that are typically most challenging for shallow DOF lenses.

For my copy, AF works better for close distance shots, strangely enough. The AF actually only misbehave on distance shots (> a few meters).

I think that this lens would be better suited to a crop frame camera, I have sold the Canon f1.4 50mm in the hope of a replacement which I think will be a vain one as Canon haven't released a  non L FF prime in too many years.

Why do would the Sigma 50mm/1.4 be better on a crop?


334
Lenses / Re: Sigma 85 f/1.4 EX DG Available Soon
« on: October 15, 2010, 07:22:03 PM »
Is the Sigma 50 1.4 really all that good?

I love my sigma 50mm/1.4 optically. And the bokeh is superb. Unfortunately I've found the AF to be unreliable at distances larger than a few meters. Unless the AF has been fixed in later versions (I have an early copy), I would not recommend this lens.

Unfortunately, the sigmas I've tried have not been as reliable with AF as canons (in general). Unfortunately, because their lenses are often optically very good.

335
Lenses / Re: EF 24-70 f/2.8L Replacement [CR2]
« on: October 13, 2010, 02:42:13 PM »
So, I'll take a few steps forward to get that nice tight framing again, and that decreased distance-to-subject translates to a shallower DoF - by a factor of 1.6x.

Yes, but the perspective will have all changed, so it's not equivalent. I think we both agree that, in contrast, the imaged formed by a 50mm/2.8 lens on a FF sensor is actually equivalent to the image formed by a 31.25mm/1.75 lens on a 1.6x APS-C sensor. Actually equivalent (identical!), in terms field of view, photon collection rate per solid angle, depth of field. No difference.

336
Lenses / Re: EF 24-70 f/2.8L Replacement [CR2]
« on: October 13, 2010, 02:30:59 PM »
Photozones test of the 24 - 105mm f/4 IS on FF wasn't what I wanted to see, it has problems with edge softness vignetting, distortion, and its minimum focus distance and magnification leave a lot to be desired.  It's useless for close up work, the 17 - 55mm is much closer to the 24 - 70mm here.

As I already wrote, according to the photozone tests themselves, 24-105mm/4.0L on 5D2 is at least as good as 17-55mm/2.8 on 7D, at least if we're talking IQ (7D has other advantages). I confirmed it with my own tests. In other words, the 17-55mm/2.8 on 7D is just as useless as 24-105mm/4.0L on 5D2.

f/2.8 on APS-C gives about the same viewfinder brightness as f/4.5 on FF. Why is that? Because in order to view the full field of view in the same solid angle, the FF viewfinder needs to compress the image (almost) 1.6x more than the APS-C viewfinder -> increasing the surface brightness. This is easy to test yourself: mount the 17-55/f2.8 on a 7D and the 24-105/4L on a 5D2. Which viewfinder is brightest? They're about the same (the 5D2 has a slightly larger apparent field in the viewfinder, but it's compensated by the lens being 4.0 instead of 4.5). If you don't believe me try it! (Of course, your 24-70mm/2.8L lens will be much brighter on the 5D2.)

337
Lenses / Re: EF 24-70 f/2.8L Replacement [CR2]
« on: October 13, 2010, 05:23:37 AM »
So you don't agree that 50mm/2.8 on a FF is identical to 31.25mm/1.75 on 1.6 APS-C? Or is it something else?

Yes I don't agree with that, f/2.8 is f/2.8 regardless of the crop factor

Ok, good, then I understand. You are right, that for the same lens the aperture doesn't change when you go from FF to crop. That would be weird. But now think of two different lenses that both share the same entrance pupil - say 18mm in both cases - but where the focal length is different, namely 50mm in one case and 31.25mm in the other. Then the image on a FF with the 50mm lens would be identical to the image of the 31.25mm on the 1.6x APS-C. And, also note, since the entrance pupil is the same, the f/#-number changes: 50/18 = 2.8 while 30/18 = 1.75. Which is what I stated in the quote above.

338
EOS Bodies / Re: Lenses in 2011 [CR2]
« on: October 13, 2010, 05:12:36 AM »
I don't know what's going on, but surprisingly The Digital Picture has the TS-E 24mm just trouncing the EF 24mm f/1.4

I think it's because the the EF 24/1.4L II is strongly optimised for wide open 1.4 performance, which is very different from 3.5. It is reasonable that photographers would use the 24/1.4 wide open a lot of the time, since it's the defining feature of the lens. You may also note that the EF 24/1.4L II @ 2.8 is sharper than the EF 16-35/2.8 II @ 2.8, but the latter is sharper when both are @ 5.6.

I think it's the same optimisation that's been done for the EF 50mm/1.2L, where its much cheaper brethren beats it in terms of sharpness for smaller apertures.

So, in conclusion, if you don't care too much after low-light performance (or very shallow DOF) but are more interested in having the ultimate sharp lens (as commonly the case in landscape photography), the slower lenses might be better for you. They're also often cheaper (though not the TS-E 24/3.5L II, obviously). The only caveat is that almost all of the non-L primes are of old design, and as we know from the recent L-updates (during the last couple of years) that performance tends to improve a lot with an update.

339
Lenses / Re: EF 24-70 f/2.8L Replacement [CR2]
« on: October 13, 2010, 04:46:24 AM »
Unfortunately that's not so epsiloneri, you're counting the crop factor twice.

Thanks for your comment, but you're not being very clear. What is not so? Please be very precise and refer to the exact statement you don't agree with, otherwise I have no hope in following you.

So you don't agree that 50mm/2.8 on a FF is identical to 31.25mm/1.75 on 1.6 APS-C? Or is it something else?

Just to make it more complicated though, not all cameras share the same bayer matrix, they can be stronger or weaker, then there's the anti aliasing filter, and they're not all the same either, not the microlenses.  It's very difficult to compare like with like.

Yes, there are other effects, but they are less significant by comparison ("second order corrections") and more about engineering than fundamental physics.

340
Lenses / Re: EF 24-70 f/2.8L Replacement [CR2]
« on: October 12, 2010, 07:46:24 PM »
Perhaps you would explain the change in focal length in the wrong direction?  50mm on FF is the same FOV as a 30mm (nearest equivalent) on a 1.6 crop, the aperture values would not change, DOF might depending on conditions

I don't think I understand. Yes, 50mm on FF shows approximately the same field as 30mm on 1.6x APS-C. You didn't state the aperture values, so I don't know what you mean when you write that they don't change. In relation to what? Focal length and aperture (as in entrance pupil) are independent quantities, and the f-number is their ratio.

Let's put it this (trivial) way. 50mm/2.8 on 1.6x APS-C is exactly the same as 50mm/2.8 on FF, where only the central 1/1.6 = 62.5% (in linear dimension) of the frame is used.

With shorter focal length, you compress solid angle onto a smaller part of the detector; so with 31.25mm you compress the same field on the APS-C as the 50mm does on the FF. If we assume that the entrance pupil is the same, that is, the same number of photons per solid angle is captured for both lenses, then that implies that the photon density at the detector must be higher for the 30mm lens (because the same number of photons were compressed onto a 1.6^2 smaller area). That is, the f-number is sqrt(1.6^2) = 1.6 smaller.

I'm sorry if my explanations are confusing, I'm sure there is a good web page somewhere which explains things better.

341
EOS Bodies / Re: Lenses in 2011 [CR2]
« on: October 12, 2010, 07:10:57 PM »
The Nikon FX 24 1.4 , 35 1.4, 50 1.4 and 85 1.4 are really excellent, Canon has some catching-up to do. Canon has never had anything like the 105 2.0DC and 135 2.0 DC lenses, why not?

I agree that many Canon primes are in dire need for update and that Nikon seem to have more attractive versions, though I would have thought  the EF 24/1.4L II to be a good match to the Nikon FX 24/1.4. I'm not too familiar with the Nikon lineup, but in what way are the Canon EF 100/2.0 USM and EF 135/2.0L USM nothing like the Nikon 105/2.0 DC and 135/2.0 DC lenses? Do the Nikons have significantly better IQ? Or do they have some other desirable property (IS? Low weight? Certainly not price?)?


342
Lenses / Re: EF 24-70 f/2.8L Replacement [CR2]
« on: October 12, 2010, 06:41:37 PM »
While the effective field of view on a crop camera may be the same as a longer lens on a 35mm, the focal length does not change and therefore neither does the aperture.  A 17 - 55mm lens may give the same FOV as a 27 -88mm but it's still a 17 - 55mm and the relationship between the first element and the focal length remains unchanged as does the aperture.

You're right, but what is your point? The focal length just gives the image scale. 50mm/2.8 on FF gives exactly the same field (solid angle) as 80mm/4.5 on 1.6x APS-C (barring lens distortion). The flux of incoming photons per solid angle will be the same. The DOF will be the same. If the detectors have the same number of pixels with the same sensitivity (say fraction of photons actually detected, also called quantum efficiency) and read-out noise, dark current etc, then the resulting image will be statistically identical in all respects.

The lens is just an optical system to capture photons and compress them to a small image. The advantage of FF sensors is not that they are inherently more sensitive. The advantage is that it's easier to make optics that produce larger image scales (e.g., it's easier to produce a good EF 80mm/1.2 lens than an EF-S 50mm/0.75 lens).

343
Lenses / Re: EF 24-70 f/2.8L Replacement [CR2]
« on: October 12, 2010, 06:09:31 PM »
So, bottom line, if you are waiting for a 24-70mm f/2.8L IS because you want a FF-equivalent of your 17-55mm IS, you can have that right now as the 24-105mm f/4L IS.

You're right, and that was exactly my point :) Jason was complaining that his 24-105/4L wasn't as good on his 5D2 as his 17-55/2.8 had been on his 50D, and I was surprised, because I thought the 24-105/4L would be similar but slightly better, if anything. I then went on and tested a 17-55/2.8  on a 7D and a  24-105/4L on a 5D2, and found that the latter was indeed very similar, but slightly better performer (for my copies).

But the bottom line is that I do not find slightly better compelling enough to go FF. A good 24-70mm f/2.8L IS on the other hand would convert me in an instant.

344
Lenses / Re: EF 24-70 f/2.8L Replacement [CR2]
« on: October 11, 2010, 07:24:42 PM »
Just FYI Justin, I got access to exactly your setup (5D2+24-105/4L) and took the opportunity to compare it to my 7D+17-55/2.8. Tripod, no IS, with a boring bookshelf as the subject. Manual focusing of centre with live view, remote shutter release with mirror lock up. Focal plane parallel to bookshelf. 24-105/4L @ 70mm (supposedly its worst focal length), 17-55/2.8 @ 44mm (the equivalent). iso 160 and 1s exposure for 5D2, iso 100 and 1s exposure for 7D (gives the same exposure level).

Result: Sharpness about equal in corners, 24-105/4L better in centre.

Then I stepped down the aperture 2 steps (i.e. to 8.0 and 5.6, respectively) and increased exposure time to 4s.

Result: 24-105/4L@8.0 improved corners significantly, and center somewhat, clearly out-resolving the 17-55/2.8@5.6, which didn't improve as much compared to wide open.

Conclusion: The resolution of the 5D2+24-105/4L is no worse than 7D+17-55/2.8, so have no remorse for selling your EF-S lens.

(NB, I can't guarantee that my results are typical, maybe I received a good 24-105/4L copy and a poor 17-55/2.8, but what I find is in line with expectations from MTF measurements)

If you're interested I can find a way to post relevant crops of the images.

345
Lenses / Re: EF 24-70 f/2.8L Replacement [CR2]
« on: October 05, 2010, 05:06:33 PM »
In terms of sharpness, I have to stop down to f11 on the 24-105 at 70mm to get even close to the 17-55 at the long end.

That is surprising, I haven't seen complaints on the sharpness of the 24-105/4L IS before (most complaints are about the strong barrel distortion at 24mm). Perhaps you have a bad copy/AF problems? According to MTF measurements by photozone.de, the 24-105/4L on 5D2 should be slightly sharper than 17-55/2.8 on 50D (although the latter is better than 24-105/4L on 50D; this is because of the APS-C 1.6x center resolution disadvantage compared to FF). It also seems the 24-105/4L is at its worst in the corners at 70mm (but still better than 17-55/2.8 at 55mm).

But yes, I'm very fond of my 17-55/2.8 IS lens and, just as you, I'm waiting for a normal F/2.8 zoom with IS to switch to FF (e.g., 24-70/2.8L IS). Even with a good calibrated copy, merely doing "slightly better" is not big enough incentive for me to switch.

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