According to diglloyd's review of the Sigma 50/1.4 on the for-fee portion of his site, the Sigma suffers from focus shift to almost exactly the same extent as the Canon 50/1.2. diglloyd provides focus test chart images for both the Sigma and the Canon (as well as other fast primes) that clearly demonstrate this. Given the outcry against the Canon 50/1.2 for its focus shift, I'm surprised there isn't a similar cry against the Sigma 50/1.4. Have any of you Sigma 50/1.4 users noticed focus shift with your lens?
Galibier wrote:
According to diglloyd's review of the Sigma 50/1.4 (...) I'm surprised there isn't a similar cry against the Sigma 50/1.4. Have any of you Sigma 50/1.4 users noticed focus shift with your lens?
I have owned both the lenses mentioned and I have tested them carefully. The 50L has a terrible focus shift where the original focus plane isn't covered by the DOF when stopping down. The Sigma 50/1.4 EX also has a focus shift. The difference to the 50L is thatthe Sigma focus shift is much less dramatic and that the focal plane (as dialed in with the lens wide open) is covered by the DOF.
The focusing problems with the SIgma seems to vary from one copy of the lens to another and the lens may front or backfocus differently depending on the shooting distance. That's enough to cry against. The focus shift is small and not a problem with the Sigma.
I tried to check what this digllouyd saud about it but the site asked for a password when clicking on the Sigma 50 EX-article. Did he get worse results than these:
If a lens focus shifts like the 50mm L lens, why can't Canon program this shift into its AF algorithm? In other words, adjust the focus according to the aperture chosen?
Jonas B -- diglloyd's images showed the Sigma's focus shift to be only slightly less than the Canon's, but with both the DOF only barely covered the intended point of focus. So yes, his results showed greater focus shift than yours.
robsteve -- you raise a good question. I know of no reason why AF algorithms could not compensate for focus shift; after all, lenses already pass aperture and subject distance information to the camera. Reportedly, Ricoh was able to adjust AF to compensate for focus shift many years ago. Why not Canon (and Sigma) now?
Galibier wrote:
Jonas B -- diglloyd's images showed the Sigma's focus shift to be only slightly less than the Canon's, but with both the DOF only barely covered the intended point of focus. So yes, his results showed greater focus shift than yours.
Then there are sample differences. I didn't expect that.
As I had owned the 50L for some time when buying the Sigma I was well aware of the focusing shift problems and I carefully tried the Sigma for this. It was way better than the 50L in every test I run with regards to focus shift.
I run into focusing problems though, just as most other people. Visiting Sigma having the lens calibrated didn't do much (not for the 450D and also not for the 5D at a second visit).
(Just to make sure in case anyone wonder:
The three images I posted were of course focused once (manually with Live View) and then I didn't touch the lens. They were also the worst samples I got. For example, when shooting the USAF charts resolution increased just as one can expect it to do when stopping down.)
Jonas, try having Canon calibrate your camera to their in house reference lens. It turned out the problem for me was the camera, not the lens. The Canon repair guy acknowledged that my camera was completely misaligned, leaving the focus point way out.
Would/did that do anything for erratic focusing at longer distances? I had my lens calibrated, and it seems like it could be a little better. When it's on, it's good, but it is a little inconsistent. ovredal73 wrote:
Jonas, try having Canon calibrate your camera to their in house reference lens. It turned out the problem for me was the camera, not the lens. The Canon repair guy acknowledged that my camera was completely misaligned, leaving the focus point way out.
ovredal73 wrote:
Jonas, try having Canon calibrate your camera to their in house reference lens. It turned out the problem for me was the camera, not the lens. The Canon repair guy acknowledged that my camera was completely misaligned, leaving the focus point way out.
My 5D was calibrated by Canon Sweden between the two visits it made, together with the lens, at Sigma Scandinavia. There was no improvement; the camera and lens combo still focused at random (my Canon lenses worked fine). That was a very unfortunate result and it later made me return the lens to the shop. Also see my next reply.
joekraft wrote:
Would/did that do anything for erratic focusing at longer distances? I had my lens calibrated, and it seems like it could be a little better. When it's on, it's good, but it is a little inconsistent.
It didn't help my 5D/Siggy50 combo. I can't tell why really. I reallt tried to coop with the lens as it optically is my fast 50mm favourite (and I have tried about 10 different 50/1.4 lenses).
Here are, loosely presented, some of the test images I finally gave to my vendor:
Well Jonas, it sounds like you exhausted your avenues to fix it, that is too bad. Thanks for the information though. On the 70m test, were you focusing on the bike? I'm not sure I would expect very good results on that one, given how small the target would be.
joekraft wrote:
(...)On the 70m test, were you focusing on the bike? I'm not sure I would expect very good results on that one, given how small the target would be.
I used the center focusing point only aiming it to the line behind the bike. As there was nothing in the way between the camera and the target the situation was not a problem. Camera on tripod, focus was locked every time with no hesitation.
At approx 70m one would expect better, no?
One of my main concerns was that i couldn't trust the AF when shooting in daily life. Portraits were all OK and possible to adjust manually most of the times, Shooting in the street, for example at something a bit away or something at the other side of the street... No, it just didn't work.
Maybe latter lenses are better. That is what I hope at least. I was an early adopter.
I'm not sure, and technically, this may be well within spec for the camera, but my own experience with my 5D is that something that small at 70m is going to be iffy at best, that's all. I'm not saying there weren't problems with your particular lens, but I'm not sure anything that wide can *reliably* focus on a target that small at that distance. Like I said, just going from my experience with all my other lenses on this camera, others may have a different opinion. Jonas B wrote:
I used the center focusing point only aiming it to the line behind the bike. As there was nothing in the way between the camera and the target the situation was not a problem. Camera on tripod, focus was locked every time with no hesitation.
At approx 70m one would expect better, no?
joekraft wrote:
I'm not sure, and technically, (...) but I'm not sure anything that wide can *reliably* focus on a target that small at that distance.
I understand what you mean. The way I see is that the exact size of the thing I aimed at is not important. I expected a repeatable result. This is not far from "infinity" and with the camera on tripod I think it "saw" and locked at the same target (whatever it was) for every image.
When I said I expected better I was thinking of a more consistent result. Now the 70m target gave the same disappointing result as the tries at shorter distances; quite varying focusing.
The test series above were al taken after the calibration done by first Canon (the camera body) and then Sigma (the lens on that body). They are better than the initial results. My impression when giving up on the lens was that I got some front focusing on short distances, nearly OK results at 2m and more backfocusing at longer distances. Sigma calibrates the lenses at a distance of 40x the focal length, which in this case is 2m.
Jonas B wrote:
My 5D was calibrated by Canon Sweden between the two visits it made, together with the lens, at Sigma Scandinavia. There was no improvement; the camera and lens combo still focused at random (my Canon lenses worked fine). That was a very unfortunate result and it later made me return the lens to the shop. Also see my next reply.
Surprising and really unfortunate. Hope you get it again with the 5d2.
ovredal73 wrote:
Surprising and really unfortunate. Hope you get it again with the 5d2.
Oh, I'm quite sure that will happen.The Sigma 50/1.4 is made for a certain sort of bokeh aficionados and combined with the performance wide open I see no option really.
i wouldn't have gotten this lens if i didn't have a body with the af micro adjust feature. in line with lots of other online experiences, i had to dial in a considerable amount of adjustment.
(+11 got mine spot on. it is razor sharp now, though.)
mh2000 wrote:
Jonas, did you do a similar test with a Canon 50 vs. the Sigma and your camera?
I'm sorry for the late reply. I missed your post.
Yes I did. That was prior to the first try by Sigma Scandinavia to calibrate the lens. By then I had the 450D, the EF50/1.4 and the Sigma 50. The 450D didn't focus exact with the EF50 but good enough, and consistent. There was a clear difference.
I never tried the 70m target with the EF50 though.
I'm guessing your result wouldn't have been any better with the Canon EF50. I think as Joe and others have mentioned, the AF target is just too small (considering the distance) for a 50mm lens. Comparing it to the 85mm results is not realistic because the AF target is almost twice the size (at the same distance).
