Problems with 50 f1.4 & 135 f2.0 on 1.6x crop sensors

[JoaoPedro]

Hi everyone

Recently I've tested the 50mm f1.4 on a full frame (5Dii) and on a 1.6x crop sensor (T2i/550D) and realized that at f1.4, f1.8 and f2.0 the lens produces a perfectly clear image on full frame but a seriously unusable image on the cropped sensor. Seriously unusable as in severe chromatic aberrations and almost out of focus image at the center (where it was focusing). The 50mm only became usable on the crop body when stopped down to f2.8.

Has anyone experienced something like this?
Is it a bad copy of the 50 f1.4? (I don't have another at hand to test right away)
And most important: has anyone experienced something like this with a 135L f2.0?

Thanks
Joao

[Crapking]

No problems with either lens on either a 7d or 1.3x 1dIV.

[carlc]

No problem with the sigma 50mm f1.4 on my 7d.  I rented the canon 135mm f2.0 but didn't have a lot of luck.  All my fault with a slower shutter speed than I should have used for the focal length resulting in camera shake.  I was trying to shoot a dance recital in very low light.  Valuable lesson learned.

[dr croubie]

So the obvious questions first:
Autofocus or manual focus?
Tripod or handheld?
Is it only the 50/1.4, or has any other lens done this to you?

A good test would be to set up everything on a tripod, manual focus on live-view, take some test shots at a few apertures, then switch camera bodies, and do exactly the same tests (same iso, shutter speed, etc).

There should in theory be no difference between using the same lens on a different camera body, whether it's FF or crop, except if there's an AF-problem, the mount isn't seated properly (both of which will be fixed by using MF in live-view), or something very weird (like the aperture isn't stopping down to the correct value if the contact is dirty.
Sure, crop-sensors have higher pixel-density, so any value of CA (in mm) will show up as more 'pixels' wide, but that shouldn't be the difference between 'perfect' and 'unusable', it should just be 'slightly more noticeable'.

[neuroanatomist]

So the obvious questions first:
Autofocus or manual focus?

+1.  Fast primes suffer from longitudinal CA, throughout the frame (unlike lateral CA) and most noticeable in OOF areas (LoCA is aka bokeh fringing).  Fast primes shot wide have thin DoF, meaning more OOF areas.  If the AF isn't working properly on the APS-C, the results you describe make sense.  By 'not working properly' I mean not well calibrated to the T2i body (but a good match to the 5DII).  That's the situation that AF microadjustment is designed to correct, but since that feature isn't available on the T2i, sending the lenses to Canon is the only option.

The way to confirm that's the issue is to use Live View as suggested, either contrast AF (the slow one where the mirror does not flip up) or manually focus at 10x in Live View.

[dirtcastle]

With a 50mm f/1.4, I often have issues with Chromatic Aberration on both a 5DII and 40D. I've just come to accept that as a normal part of an extremely fast, and low-priced lens. For me, the solution is to avoid blowouts from f/1.4 to f/2.

I'm hoping a 50mm f/1.2 will have better AF and low CA, at which time I'll switch. I haven't had significant CA problems with my 135mm L on the 5DII, but haven't used it on a crop.

[JoaoPedro]

Tripod, ISO 1600, slowest shutter speed 125 (f4 shots) and highest 500 (f1.4).
f1.4 out of focus @ focus point
f1.6 out of focus @ focus point
f1.8 a little bit less out of focus @ focus point
f2.0 terribly out of focus @ focus point
f2.2 starts to be in focus @ focus point
f2.8 in focus @ focus point
f3.2 in focus @ focus point
f4.0 in focus @ focus point

The Canon 50 f1.4 isn't the only lens behaving like this with my 550D (1.6x crop). I once tried the 50 f1.8 and it was similar, hence the reason for not buying it. But both behaved well on the 5Dii!

All the other lenses I have (16-35L, 100, 24-70L, 70-200L f4) behave perfectly well on both cameras, crop and full frame.

Any guess?

[gene_can_sing]

Lenses always work better on crop lenses because it uses the sweet spot, so the images tend to be sharper across the board with lower CAs.

Are you sure it's not a problem with the camera?

[RedEye]

I have some trouble getting my t2i to focus with reliability, might be similar in your case.

[tjc320]

I have some trouble getting my t2i to focus with reliability, might be similar in your case.

True story.

Try to find a friend with the same camera to test the lenses on. I have a strong suspicion that it may be the camera's doing. However, you mention chromatic aberration which can only be a lens issue. However, the cropped sensor is essentially zooming into the center of the lens and can cause any lens flaws to become more apparent.

I suppose you don't have any samples for us to look at?

[nightbreath]

I have experienced similar issues, there were 2 separate problems:
1. 50 f/1.4 didn't focus properly on my 7D (front-focus issue, this lens autofocused properly on 400D though) and I sent it to Canon for camera / lens focus adjustments.
2. Camera didn't want to focus on low-contrast subjects (not sure if it is an issue or normal behavior), so I sent the camera to Canon with sample shots. Here's my thread about the issue: http://www.canonrumors.com/forum/index.php/topic,3355.0.html

Before sending your gear anywhere localise the problem and only then send it for repair. I spent few days of testing in different environment to identify what the problems were.

[Actionpix]

Canon 5DII has larger pixelsize than the 550D. (Size as 20D). Therefore it is possible problems, first not visible because they fell into one pixel, might become visible when captured on more pixels. (What you get with smaller pixels.)

[D.Sim]

if you're taking test shots on a tripod, get good lighting and drop the ISO all the way down. Probably a good idea to take shots using the usual phase detection and some on live view manual/live view contrast detection to compare like neuro has said as well....

I doubt its the lenses - especially if they're working brilliantly on the 5D already. The crop will be taking the shot from the sharpest area of the image circle.

If you can, do a microfocus adjustment (can't remember offhand if its available on the 550D), or in the case you can't, send it in to Canon (with the lenses) to be calibrated.

[vbi]

I had a couple of lenses that worked perfectly on my 40D and 5D2 but were very soft on my 7D. Drove me nuts thinking I was getting something wrong until I look into AF microadjustment. Seems my 7D was prone to front focus. Once adjusted everything works flawlessly.

Moral of the story...what works on one camera will not necessarily work as well on another.

[koolman]

Thanks for this question and post, as I'm sure the 50 1.4 + crop are a common combination for many of us, including myself.

I use the 50 1.4 all the time on my 550d for candid portraits, often even at 1.4-1.6 to allow me the fastest shutter speeds. I found that it takes skill to properly nail focus at such a thin DOF, you need something well lit and good  contrast such as eyes or other facial feature. Additionally my 550d has a slight front focus, so I use something to nail focus with that is a little further away, like the far eye, etc.

With patience I get good results. If I want super sharp, and have a more controlled environment (the model is willing to sit still) I use live view and manual focus.

You do need to note: The crops cause you to work at a farther working distance then the FF, and this makes nailing focus more challenging, as the eyes for example are smaller and less bold contrasty then closer up.