Ok, so my new 50mm L f/1.2 arrived today from B+H. The date code is UY. First thing I did was test for focus shift and the good news is I couldn't see one. I tested it at 0.5m and 1.5m distance. Now the bad stuff, the lens is really soft between 1.2-1.8. At 2.0 and higher it's great. So now I'm not sure if I should try to get a different copy or not. I'm happy about the lack of shift focus, but not happy about the wide open sharpness. I was expecting it to be softer than usual, but not this soft. Please see the images below and let me know what you think. All shots were on tripod, Canon 5D, ISO 100. This is just a sample from about 300 photos I took all with pretty much the same result. Changing distance to subject did not make any significant difference. I guess I'm trying to figure out if this is a typical performance from this lens and trying to exchange it would not make any improvements.
pcvrz22g wrote:
Have you checked for front/back focus?
Yes and there is none. Tried ton of chart tests at 45 degrees from various distances and no front/back focus. The sharpness and contrast are just lacking at 1.2-1.8. I feel lucky about not having the famous focus-shift problem for sure.
Plug your numbers into a depth of field calculator and you will see at those distances DOF is pretty thin. Just a little front or back focus and you're pretty well going to be out of focus. At 1.2, you just don't get much DOF. Are you expecting too much perhaps?
Now decide whether or not you feel the performance of your copy is consistent with the test charts.
Yeah, I just looked at those and they look pretty much like what I'm seeing. I'm trying to see what results do the members of this forum have.
wickerprints wrote:
What was your focus shift testing methodology? Variety of test charts, newspapers at 45 degree angle, tripod, distance of 0.5, 1, 1.5, 3 meters and F/1.2 - F/8. Plus some real world testing around the house/backyard. I was truly scared what the results would be, and was pleasantly surprised.
As others will tell you; The focus shift that you say you don't have, is a property of the lens' optical design. It is inherent to the lens design itself so it's there, you just haven't noticed it at the specific distances. That being said, those shots do seem quite soft.
The reason why I asked about your focus shift testing methodology is because in order to conclusively determine its existence, you must test using manual focus, using either a super precision focusing screen, split-prism focusing screen, or Live View to confirm focus. The reason why is because AF confirmation on all EOS bodies cannot be any more precise than one-third the f/2.8 depth of focus, as no AF sensors are available that are able to detect phase at f/1.2.
This is why I believe some people claim not to observe any focus shift, whereas others complain quite loudly about it.
As for your testing, at longer subject distances such as in your first sample series, I think the performance is actually poorer than the test chart @ f/1.2 and slightly better than the chart @ f/2. This makes me suspect that it may not be your lens which is out of spec, but rather, your reliance on AF to confirm focus may indicate you can obtain slightly sharper results wide open. Yes, it could well be that your copy is not within spec, but due to the lack of precise AF at apertures much wider than f/2.8, this source of error must be accounted for before we point fingers at the lens.
ramblinray wrote:
Plug your numbers into a depth of field calculator and you will see at those distances DOF is pretty thin. Just a little front or back focus and you're pretty well going to be out of focus. At 1.2, you just don't get much DOF. Are you expecting too much perhaps?
The first set of shots was done at 3.5 meter distance, which means DOF of 0.35m. That should have been sufficient for those tests, especially since they're on a tripod.
The newspaper shots were done at 1.5 meters, which gives 0.06m DOF. Which is again quiet a bit with a tripod.
wickerprints wrote:
This makes me suspect that it may not be your lens which is out of spec, but rather, your reliance on AF to confirm focus may indicate you can obtain slightly sharper results wide open.
Good idea, I'll retest with manual focus. Luckily I do have the Ee-S screen. When I auto focused it seemed correct, but who knows...
While the focus shift is a lens design, if you aren't seeing it, I wouldn't worry about it. Some copies shift way more than others and it sounds like you got one with minimal shifting. So minimal that it stays within DOF limits.
As for the wide open softness, I wouldn't say it's soft, but it's "ghostly". No contrast and lack the punch/crispness. That's typical when you are shooting text on white paper, which I am assuming you won't do normally.
However looking at the crops from the first few images, they look rather soft. I would guess that the lens is backfocusing. (Not shifting, just back focusint) That's pretty common with this lens. You can either play the never ending game with Canon and send it for calibration, or return it and hope for a better copy.
Both 100% crops are blue green. That is a sign of longitudinal chromatic aberration, LoCA, when the subject if out of focus, with the in focus area in front of the subject. If the in focus area would be behind the subject the colour of the LoCA would be redish.
That's pretty bad, IMO, considering the cost of the glass. I don't know if it's typical, but I'd say that if it is you're better off with the Sigma or even the Canon 1.4.
The whole point of that fast lens is it's performance at it's largest aperture so I'd say get on the phone with B&H, at least to firm up or extend your two week return priviledge while you figure out what to do.
Z250SA wrote:
Both 100% crops are blue green. That is a sign of longitudinal chromatic aberration, LoCA, when the subject if out of focus, with the in focus area in front of the subject. If the in focus area would be behind the subject the colour of the LoCA would be redish.
This was also my conclusion based on the newspaper f/1.2 crop. That green tinge only show up if focus is off. If it's green, it's front focused, if it's pink, it's back focused. The same characteristic is evident with the 85L.
I would agree with a comment above that the best way to determine correct focus is with a live view capable camera, preferably one capable of contrast detect AF, or a lot of focus bracketing, ideally on a focusing rail.
Z250SA wrote:
Both 100% crops are blue green. That is a sign of longitudinal chromatic aberration, LoCA, when the subject if out of focus, with the in focus area in front of the subject. If the in focus area would be behind the subject the colour of the LoCA would be redish.
+1
same opinion, a slight FF;
that's the reason for you did'nt detect a shift focus; first issue hides the second ;-)