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Archive 2009Focus Shift and a 50 1.2 series of photos
p.1 #1Focus Shift and a 50 1.2 series of photos
First time posting images so I hope it goes well. I've resized a series of photos to 640 pixels on the long side per Image Upload instructions. The series includes 17 photos of a line of books taken from aperture 1.2 through 8.0 using my 50 1.2L lens. Each book is 1/4 inch further back from the prior one starting from the left and moving to the right. The focus point is the center focus point and is on the top gold leaf symbol under "Dickens" of the center book entitled "Little Dorrit" in all shots. All taken with an MT-24 EX ringlight flash mounted on the front of the lens at a distance of approximately 19 inches from the book on the left to the focal plane of the camera. The first image E3J3373 is at 1.2 and the others follow in sequence, 1.4, etc.
I apologize for any sarcasm anyone may have detected in my prior post in another thread regarding the photographic utility of using this lens under these circumstances. Focus shift just hasn't been an issue with my shooting styles and this lens. I hope this is helpful in an evaluation of the focus shift question.
Edited on Mar 19, 2009 at 06:08 PM · View previous versions
I apologize for any sarcasm anyone may have detected in my prior post in another thread regarding the photographic utility of using this lens under these circumstances. Focus shift just hasn't been an issue with my shooting styles and this lens. I hope this is helpful in an evaluation of the focus shift question.
Edited on Mar 19, 2009 at 06:08 PM · View previous versions
Mar 19, 2009 at 03:57 PM
p.1 #2Focus Shift and a 50 1.2 series of photos
Where's the huuuge shift everybody's talking about? 
Mar 19, 2009 at 04:13 PM
p.1 #3Focus Shift and a 50 1.2 series of photos
Not sure what this proves other than that the fact that YOU obviously have a 50L that doesn't shift beyond DOF limits. Good for you. I am happy for you. I really am.
I just don't understand the stubborness to at least acknowledge that this is not some sensationlized and imaginary issue. Why is it that some apparently have the strong desire to disprove those who have had issues with the 50L?
I can put a sequence of shots too that shows the focus shift in all its glory and from 3 different copies too...but what would be the point. Folks would just call me names like "hobbyist", "gear head", "pixel peeper", and tell me to go out and shoot in the real world.
But what the heck, if we are putting up shots of rows of books, might as well put up the charts I took when I had to send in the 50L to Canon...a whole 5 times. Same sh*t different smell right? And before you mention anything about shooting charts, I have never shot one before the 50L, and I have not shot one since. I'm not sure what that proves, but I figured I'll throw that little tidbit out there...
f2.8 100% crop
http://nicksan.zenfolio.com/img/v4/p99167901.jpg
f5.6 100% crop
http://nicksan.zenfolio.com/img/v4/p139732022.jpg
Niiiice....
How close was I?
2-3 feet away...
http://nicksan.zenfolio.com/img/v4/p174747066-5.jpg
Tripod, remote release, timer, MLU...yada, yada, yada...
What does this prove? It proves that MY copy was shifting badly. That's all it proves. But what I can also claim is that I have used 5 different copies of this lens and they all pretty much do the same thing.
Draw your own conclusions...
I just don't understand the stubborness to at least acknowledge that this is not some sensationlized and imaginary issue. Why is it that some apparently have the strong desire to disprove those who have had issues with the 50L?
I can put a sequence of shots too that shows the focus shift in all its glory and from 3 different copies too...but what would be the point. Folks would just call me names like "hobbyist", "gear head", "pixel peeper", and tell me to go out and shoot in the real world.
But what the heck, if we are putting up shots of rows of books, might as well put up the charts I took when I had to send in the 50L to Canon...a whole 5 times. Same sh*t different smell right? And before you mention anything about shooting charts, I have never shot one before the 50L, and I have not shot one since. I'm not sure what that proves, but I figured I'll throw that little tidbit out there...
f2.8 100% crop
http://nicksan.zenfolio.com/img/v4/p99167901.jpg
f5.6 100% crop
http://nicksan.zenfolio.com/img/v4/p139732022.jpg
Niiiice....
How close was I?
2-3 feet away...
http://nicksan.zenfolio.com/img/v4/p174747066-5.jpg
Tripod, remote release, timer, MLU...yada, yada, yada...
What does this prove? It proves that MY copy was shifting badly. That's all it proves. But what I can also claim is that I have used 5 different copies of this lens and they all pretty much do the same thing.
Draw your own conclusions...
Mar 19, 2009 at 09:39 PM
p.1 #4Focus Shift and a 50 1.2 series of photos
You wanna here something more interesting?
I've discovered that at least on my particular copy of the 50L and my 1DMKIII, putting the camera in AI-servo mode yields better results.
In fact the 50L acts like a different lens entirely...no joke. It's BANG on when put in Servo mode. (By this I mean against static subjects...the 50L pretty much sucks when tracking moving objects, at least that's been my experience...)
Go figure...we alll figure out workarounds right?
I've discovered that at least on my particular copy of the 50L and my 1DMKIII, putting the camera in AI-servo mode yields better results.
In fact the 50L acts like a different lens entirely...no joke. It's BANG on when put in Servo mode. (By this I mean against static subjects...the 50L pretty much sucks when tracking moving objects, at least that's been my experience...)
Go figure...we alll figure out workarounds right?
Mar 19, 2009 at 09:45 PM
p.1 #5Focus Shift and a 50 1.2 series of photos
What you dont take into account is that as you stop down the increase in DOF should also move forward also more so than the dof moves rearward so you do indeed exhibit focus shift. Only till you get to f5 does the book to the left get sharper. The focus shift is inherit in the lens design. It is not a QC issue.
Edited on Mar 19, 2009 at 10:05 PM · View previous versions
Edited on Mar 19, 2009 at 10:05 PM · View previous versions
Mar 19, 2009 at 10:02 PM
p.1 #6Focus Shift and a 50 1.2 series of photos
What you dont take into account is that as you stop down the increase in DOF should also move forward also more so than the dof moves rearward so you do indeed exhibit focus shift. Only till you get to f5 does the book to the right get sharper
Mar 19, 2009 at 10:03 PM
p.1 #7Focus Shift and a 50 1.2 series of photos
Nick writes, "Not sure what this proves other than that the fact that YOU obviously have a 50L that doesn't shift beyond DOF limits. Good for you. I am happy for you. I really am."
J. Allen's test simulates real photographic situations much better than an inclined ruler or scale. I've tried shooting inclined rulers and noticed the center AF point covers a very large area and will focus below center and the next time above. And maybe the next time dead center. Of course I don't have a 1D so I'm sure my prosumer AF isn't as surefooted. However the book test has proved to be a lot easier on the AF systems of my 5D and 50D. My 50 1.2L results are very similar to J. Allen. I'm happy with my 50 1.2L and it rarely misses AF for me.
J. Allen's test simulates real photographic situations much better than an inclined ruler or scale. I've tried shooting inclined rulers and noticed the center AF point covers a very large area and will focus below center and the next time above. And maybe the next time dead center. Of course I don't have a 1D so I'm sure my prosumer AF isn't as surefooted. However the book test has proved to be a lot easier on the AF systems of my 5D and 50D. My 50 1.2L results are very similar to J. Allen. I'm happy with my 50 1.2L and it rarely misses AF for me.
Mar 20, 2009 at 02:00 AM
p.1 #8Focus Shift and a 50 1.2 series of photos
I'll tell you, Canon will, and so will countless others, that shooting a poorly-lighted, inclined ruler is simply not a valid way to test AF accuracy. The angled books truly do work better, but again, poor lighting can come into play, and I'll only attempt such methods in bright, natural light. I happen to like using canned goods, as odd as that may sound, and they've never let me down, usually providing nice bright, contrasty media and a barcode. Michael Tapes' LensAlign gadget also does a great job, with easily repeatable results, but you'll notice the focus test is done using the vertical target, while the diagonal ruler is there just as an indicator.
Any time you guys post shots showing AF issues, I'm happy to take a look and try to discuss the possible issue, but when I see a diagonal ruler shot, I just cringe and wonder how this method even came into existence. The originator should be hung out to dry by his toes, sort of like the guy who tried to light his shoe on fire while flying, resulting in us all having to take our shoes off at the airport.
As silly as the shot below looks, it takes two seconds to set up, and it works every time. I shoot hand-held, in natural light, just as I would if I were out using my gear for fun.
http://deanwcains.smugmug.com/photos/434820042_j2cbf-L.jpg
BTW, this is the setup I used to tweak the AF on my ancient 10D, using my EF 50/1.4 wide-open, and that body has never performed as well (with all my lenses), even when it was new almost 6 years ago. Trying the same adjustments with the angled ruler method on my dim dining room table would have been futile.
Any time you guys post shots showing AF issues, I'm happy to take a look and try to discuss the possible issue, but when I see a diagonal ruler shot, I just cringe and wonder how this method even came into existence. The originator should be hung out to dry by his toes, sort of like the guy who tried to light his shoe on fire while flying, resulting in us all having to take our shoes off at the airport.
As silly as the shot below looks, it takes two seconds to set up, and it works every time. I shoot hand-held, in natural light, just as I would if I were out using my gear for fun.
http://deanwcains.smugmug.com/photos/434820042_j2cbf-L.jpg
BTW, this is the setup I used to tweak the AF on my ancient 10D, using my EF 50/1.4 wide-open, and that body has never performed as well (with all my lenses), even when it was new almost 6 years ago. Trying the same adjustments with the angled ruler method on my dim dining room table would have been futile.
Mar 20, 2009 at 02:54 AM
p.1 #9Focus Shift and a 50 1.2 series of photos
Agree fully with ggg and dcains. I had a lot of difficulty using the ruler method from a consistency perspective. Results varied to the point where I began to attribute the issue to camera AF rather than the lens (I use 1-series bodies along with a 5D). I ended up using a very well-lighted flat surface adjacent to a large north-facing window on a bright day to try to obtain reasonably consistent, accurate results. And even then I had doubts that the results were representative. My alternative was to shoot an angled lens box in the best natural light I could manage. Upshot is the book/can/lens box based testing serves better, imho.
Congrats to J Allen for reverting to more objective discussion. Appreciate you taking the time to do the testing and sharing.
Hey Nick, maybe focus testing with a Mk III is part of the problem
Congrats to J Allen for reverting to more objective discussion. Appreciate you taking the time to do the testing and sharing.
Hey Nick, maybe focus testing with a Mk III is part of the problem
Mar 20, 2009 at 04:56 AM
p.1 #10Focus Shift and a 50 1.2 series of photos
People who don't even know the difference between focus shift and front/backfocus shouldn't post in this thread. 
Again, the issue has nothing to do with AF.
Again, the issue has nothing to do with AF.Mar 20, 2009 at 05:15 AM
p.1 #11Focus Shift and a 50 1.2 series of photos
That's true. My reply was in regard to the methodology, not the focus shift issue.
Mar 20, 2009 at 05:51 AM
p.1 #12Focus Shift and a 50 1.2 series of photos
I think the inclined Jackson focus test chart is a legitimate way to demonstrate the existence of focus shift, assuming the first (widest-aperture) shot is correctly focused, and the lens is not re-focused thereafter. However, I believe the chart also exaggerates the effect of focus shift, and doesn't accurately portray how focus shift is likely to affect your "real world" photography, whatever that may be. J. Allen's test is, in my opinion, a much better demonstration of the effect of focus shift in the "real world." His test parallels my experience with the 50/1.2: yes focus shift exists, but it is so slight that it affects the accuracy of focus much less than other factors, such as camera or subject movement, lighting, contrast, and AF point size. In fact (and I'm repeating myself here), I have never been able to discern focus shift in any of my "real world" shooting.
Nick, I don't think J. Allen's test suggests stubborness or a strong desire to disprove anyone. The test is what it is, and it shows how his lens performs. It is another data point. What continues to puzzle me, though, is how the degree of focus shift can evidently vary so greatly, with people reporting focus shift so severe that the 50/1.2 is unuseable at certain apertures (focus moving from the eyes to the ears, for example). I would have thought that focus shift is an essentially consistent characteristic of a lens, like distortion and vignetting. Can anyone explain how focus shift can vary from copy to copy?
Nick, I don't think J. Allen's test suggests stubborness or a strong desire to disprove anyone. The test is what it is, and it shows how his lens performs. It is another data point. What continues to puzzle me, though, is how the degree of focus shift can evidently vary so greatly, with people reporting focus shift so severe that the 50/1.2 is unuseable at certain apertures (focus moving from the eyes to the ears, for example). I would have thought that focus shift is an essentially consistent characteristic of a lens, like distortion and vignetting. Can anyone explain how focus shift can vary from copy to copy?
Mar 20, 2009 at 06:36 AM
p.1 #13Focus Shift and a 50 1.2 series of photos
Shuko wrote:
People who don't even know the difference between focus shift and front/backfocus shouldn't post in this thread. Again, the issue has nothing to do with AF.
+1
Agreed.
The important question is when is Canon ever going to do something about it?
People who don't even know the difference between focus shift and front/backfocus shouldn't post in this thread.
Again, the issue has nothing to do with AF.+1
Agreed.
The important question is when is Canon ever going to do something about it?
Mar 20, 2009 at 08:29 AM
p.1 #14Focus Shift and a 50 1.2 series of photos
This is exactly why I said the pics of the charts proves nothing to anyone else but myself and really, the only reason why I am even responding is because there seems to be a group of people accusing those with 50L issues of not being "real photographers". I fail to see what that has to do with anything.
I can't speak for other folks who aren't 100% in love with the 50L, but I never recall ever saying that all copies exhibit the shift. They all do shift, but there are many happy owners who don't see the shift because it stays within DOF limits. For all intents and purposes, these are "good" copies.
But this thread was most likely in response to the other thread where things got a little out of hand and we need to be fair about the facts of life of the 50L.
No bashing. No fan-boy-ism. Just the cold hard facts.
Or is the 50L debate much like politics?
Gochugogi wrote:
J. Allen's test simulates real photographic situations much better than an inclined ruler or scale. I've tried shooting inclined rulers and noticed the center AF point covers a very large area and will focus below center and the next time above. And maybe the next time dead center. Of course I don't have a 1D so I'm sure my prosumer AF isn't as surefooted. However the book test has proved to be a lot easier on the AF systems of my 5D and 50D. My 50 1.2L results are very similar to J. Allen. I'm happy with my 50 1.2L...Show more →
I can't speak for other folks who aren't 100% in love with the 50L, but I never recall ever saying that all copies exhibit the shift. They all do shift, but there are many happy owners who don't see the shift because it stays within DOF limits. For all intents and purposes, these are "good" copies.
But this thread was most likely in response to the other thread where things got a little out of hand and we need to be fair about the facts of life of the 50L.
No bashing. No fan-boy-ism. Just the cold hard facts.
Or is the 50L debate much like politics?
Gochugogi wrote:
Earlier quote
Nick writes, "Not sure what this proves other than that the fact that YOU obviously have a 50L that doesn't shift beyond DOF limits. Good for you. I am happy for you. I really am."Mar 20, 2009 at 09:24 AM
p.1 #15Focus Shift and a 50 1.2 series of photos
What I find interesting is all my other lenses are pretty much spot on regardless of method used. The only reason why I ran tests on my other lenses was b/c after the 50L debacle, I became curious how they would do. I ran them through tests once, and never again.
So honestly, it just sounds like some people are making excuses for the $1400 50L.
Mike Tuomey wrote:
Agree fully with ggg and dcains. I had a lot of difficulty using the ruler method from a consistency perspective. Results varied to the point where I began to attribute the issue to camera AF rather than the lens (I use 1-series bodies along with a 5D). I ended up using a very well-lighted flat surface adjacent to a large north-facing window on a bright day to try to obtain reasonably consistent, accurate results. And even then I had doubts that the results were representative. My alternative was to shoot an angled lens box in the best natural light...Show more →
So honestly, it just sounds like some people are making excuses for the $1400 50L.
Mike Tuomey wrote:
Agree fully with ggg and dcains. I had a lot of difficulty using the ruler method from a consistency perspective. Results varied to the point where I began to attribute the issue to camera AF rather than the lens (I use 1-series bodies along with a 5D). I ended up using a very well-lighted flat surface adjacent to a large north-facing window on a bright day to try to obtain reasonably consistent, accurate results. And even then I had doubts that the results were representative. My alternative was to shoot an angled lens box in the best natural light...Show more →
Mar 20, 2009 at 09:26 AM
p.1 #16Focus Shift and a 50 1.2 series of photos
An objective discussion would include both sides of the story, not just a personal account of this lens.
But I agree, the tone of these posts are much better than the ones in the other thread. In the other one you either had a 50L love-fest or a 50L bashing party going on so.
I think the most important thing for a potential 50L buyer is to read the reviews, take them with a grain of salt, know that there MAY BE potential issues.
That's the best you could do. If you get a good copy great. If you don't, hopefully you bought from a reputable dealer with a nice return policy.
Pretty much standard operating procedure for any lens I would think...
As for the MKIII, funny comment. Except I've never had any problems with my other lenses. It is what it is...
Mike Tuomey wrote:
Agree fully with ggg and dcains. I had a lot of difficulty using the ruler method from a consistency perspective. Results varied to the point where I began to attribute the issue to camera AF rather than the lens (I use 1-series bodies along with a 5D). I ended up using a very well-lighted flat surface adjacent to a large north-facing window on a bright day to try to obtain reasonably consistent, accurate results. And even then I had doubts that the results were representative. My alternative was to shoot an angled lens box in the best natural light...Show more →
But I agree, the tone of these posts are much better than the ones in the other thread. In the other one you either had a 50L love-fest or a 50L bashing party going on so.
I think the most important thing for a potential 50L buyer is to read the reviews, take them with a grain of salt, know that there MAY BE potential issues.
That's the best you could do. If you get a good copy great. If you don't, hopefully you bought from a reputable dealer with a nice return policy.
Pretty much standard operating procedure for any lens I would think...
As for the MKIII, funny comment. Except I've never had any problems with my other lenses. It is what it is...
Mike Tuomey wrote:
Agree fully with ggg and dcains. I had a lot of difficulty using the ruler method from a consistency perspective. Results varied to the point where I began to attribute the issue to camera AF rather than the lens (I use 1-series bodies along with a 5D). I ended up using a very well-lighted flat surface adjacent to a large north-facing window on a bright day to try to obtain reasonably consistent, accurate results. And even then I had doubts that the results were representative. My alternative was to shoot an angled lens box in the best natural light...Show more →
Mar 20, 2009 at 09:34 AM
p.1 #17Focus Shift and a 50 1.2 series of photos
This is fair. I agree.
I think part of the problem with the variance of the shift, or the apparent variance, is that on top of the shift, many of these copies has regular back focus issues.
I had my old 50L exchanged with a brand spanking new one directly by Canon. UW0706 date code. That thing back focused as well, requiring a MFA of 10-. Ironically, I needed to send that one back to get it calibrated and it still back focuses. Better, but not as spot on as any of my other lenses.
However we all know MFA does nothing for shifting. But I can tell you that my current copy is just light years better than my old copy and really, I think I probably have one of the better copies out there now and that's really the only reason why I kept it.
I often times use my 50L as a walkaround lens and it excels at that. And shooting at distances > 6ft, I just don't worry about things that much.
So I know the workarounds with my specific copy now. But getting there was a royal pain in the butt!
Galibier wrote:
I think the inclined Jackson focus test chart is a legitimate way to demonstrate the existence of focus shift, assuming the first (widest-aperture) shot is correctly focused, and the lens is not re-focused thereafter. However, I believe the chart also exaggerates the effect of focus shift, and doesn't accurately portray how focus shift is likely to affect your "real world" photography, whatever that may be. J. Allen's test is, in my opinion, a much better demonstration of the effect of focus shift in the "real world." His test parallels my experience with the 50/1.2: yes focus shift exists, but it...Show more →
I think part of the problem with the variance of the shift, or the apparent variance, is that on top of the shift, many of these copies has regular back focus issues.
I had my old 50L exchanged with a brand spanking new one directly by Canon. UW0706 date code. That thing back focused as well, requiring a MFA of 10-. Ironically, I needed to send that one back to get it calibrated and it still back focuses. Better, but not as spot on as any of my other lenses.
However we all know MFA does nothing for shifting. But I can tell you that my current copy is just light years better than my old copy and really, I think I probably have one of the better copies out there now and that's really the only reason why I kept it.
I often times use my 50L as a walkaround lens and it excels at that. And shooting at distances > 6ft, I just don't worry about things that much.
So I know the workarounds with my specific copy now. But getting there was a royal pain in the butt!
Galibier wrote:
I think the inclined Jackson focus test chart is a legitimate way to demonstrate the existence of focus shift, assuming the first (widest-aperture) shot is correctly focused, and the lens is not re-focused thereafter. However, I believe the chart also exaggerates the effect of focus shift, and doesn't accurately portray how focus shift is likely to affect your "real world" photography, whatever that may be. J. Allen's test is, in my opinion, a much better demonstration of the effect of focus shift in the "real world." His test parallels my experience with the 50/1.2: yes focus shift exists, but it...Show more →
Mar 20, 2009 at 09:39 AM
p.1 #18Focus Shift and a 50 1.2 series of photos
Nick Nishizaka wrote:
I think part of the problem with the variance of the shift, or the apparent variance, is that on top of the shift, many of these copies has regular back focus issues.
Nick, that is my experience. Canon corrected the back focus problem on my copy through calibration to the degree that focus shift is contained within the limits of DOF.
Galibier, I can't explain focus shift variation at all, but it would be appear that there is fair amount of back focus variation among copies. Perhaps the backfocus variation is mistaken for focus shift variation.
I think part of the problem with the variance of the shift, or the apparent variance, is that on top of the shift, many of these copies has regular back focus issues.
Galibier wrote
Can anyone explain how focus shift can vary from copy to copy?Nick, that is my experience. Canon corrected the back focus problem on my copy through calibration to the degree that focus shift is contained within the limits of DOF.
Galibier, I can't explain focus shift variation at all, but it would be appear that there is fair amount of back focus variation among copies. Perhaps the backfocus variation is mistaken for focus shift variation.
Mar 20, 2009 at 11:19 AM
p.1 #19Focus Shift and a 50 1.2 series of photos
Mike Tuomey wrote:
Nick, that is my experience. Canon corrected the back focus problem on my copy through calibration to the degree that focus shift is contained within the limits of DOF.
Galibier, I can't explain focus shift variation at all, but it would be appear that there is fair amount of back focus variation among copies. Perhaps the backfocus variation is mistaken for focus shift variation.
I think this is correct. If there is little or no back focus in the lens the focus shift stays within the DoF. If you look at the books which are staggered pretty closely to .25 of an inch and go to the f/3.2 and 3.5 shots the focus shift seems to have come into play to my eye. The DoF at those focal lengths for these shots is about .5 of an inch. With 1/3 front and 2/3 back DoF I would not expect to see as much of the second, third and fourth books to the right of Little Dorrit in focus since they are .5 to .75 of an inch behind the center of focus which means all of the DoF seems to be going to the back with a little shift thrown in for good measure. As you roll through the f stops the increase in DoF to the rear seems to continue until you get to about 5.6 where the book to the left is now in the DoF. At 5.6 there is about 1 inch of DoF which would put the book to the left in focus, and as you roll through the rest of the f stops the books to the left do appear to match the 1/3 2/3 DoF rule of thumb.
Nick Nishizaka wrote
I think part of the problem with the variance of the shift, or the apparent variance, is that on top of the shift, many of these copies has regular back focus issues.Galibier wrote
Can anyone explain how focus shift can vary from copy to copy?Galibier, I can't explain focus shift variation at all, but it would be appear that there is fair amount of back focus variation among copies. Perhaps the backfocus variation is mistaken for focus shift variation.
I think this is correct. If there is little or no back focus in the lens the focus shift stays within the DoF. If you look at the books which are staggered pretty closely to .25 of an inch and go to the f/3.2 and 3.5 shots the focus shift seems to have come into play to my eye. The DoF at those focal lengths for these shots is about .5 of an inch. With 1/3 front and 2/3 back DoF I would not expect to see as much of the second, third and fourth books to the right of Little Dorrit in focus since they are .5 to .75 of an inch behind the center of focus which means all of the DoF seems to be going to the back with a little shift thrown in for good measure. As you roll through the f stops the increase in DoF to the rear seems to continue until you get to about 5.6 where the book to the left is now in the DoF. At 5.6 there is about 1 inch of DoF which would put the book to the left in focus, and as you roll through the rest of the f stops the books to the left do appear to match the 1/3 2/3 DoF rule of thumb.
Mar 20, 2009 at 12:11 PM
p.1 #20Focus Shift and a 50 1.2 series of photos
Actually, I think depth of field should be split almost 50/50 at these distances, with slightly greater DOF to the rear. J. Allen's 50/1.2 exhibits what I think of as the standard dose of focus shift with this lens. To "fix" the focus shift would seem to require either a re-design, or firmware to re-adjust focus depending on aperture and subject distance, as Konica did some years ago. I wonder if the reported widely-varying focus performance of this lens has discouraged Canon from tackling this issue, or if they just don't consider it worth the effort.
Mar 20, 2009 at 12:35 PM