p.5 #1 · 24-105mm FOCUS SHIFT survey - FINAL RESULTS
Messier77 wrote:
I’m not sure I see a coordinated smear campaign here. We’re all enthusiasts and professionals who spend a lot of money on Sony equipment and want to see Sony’s system succeed.
I didn't mean to suggest that. I was responding to the idea that Sony's quality can't be trusted, which I think is largely an internet perpetuated myth. In this particular case, it's clear that there is something wrong, but I don't take it as an indictment of the whole company and their products.
p.5 #2 · 24-105mm FOCUS SHIFT survey - FINAL RESULTS
I would like to add to this debate - I know that the A7R2 camera focuses internally but to be sure I sent my lens 1814471 back to Sony Service Center they reported NO faults with the lens - but there is - as it only focuses in AFC mode.
p.5 #3 · 24-105mm FOCUS SHIFT survey - FINAL RESULTS
MikeEvangelist wrote:
I didn't mean to suggest that. I was responding to the idea that Sony's quality can't be trusted, which I think is largely an internet perpetuated myth. In this particular case, it's clear that there is something wrong, but I don't take it as an indictment of the whole company and their products.
I've personally been a slight bit disappointed with Sony's overall QC, but I chock that up to a few factors:
1. Going from 24mpx to 42mpx really exposes any decentering or other issues/imperfections that would probably not even be noticed otherwise.
2. Going from 1080p screens to 5k screens likewise exposes issues/imperfections. This also allows a greater proportion of buyers to easily be intensive "pixel peepers,"
3. Sony started a new system/mount from scratch, and there are difficulties and growing pains to be expected, especially as Sony did not have a long history of and extensive experience with manufacturing lenses (at least certainly not compared to Canon and Nikon).
4. They appear to be pushing some of the tolerance limits of optical design/manufacture (which is welcomed, but also comes with drawbacks).
5. Sony tends to charge more for lenses than Canon/Nikon, which makes people look at each lens as more of a very significant investment and test each lens more intensively. I'm sure their corporate and marketing department understand that by charging more/high prices, they will invite scrutiny and higher expectations. That's a basic reality of branding, pricing, consumers and market goods.
6. Some people are just unlucky and get multiple subpar copies or (and I hate to say it as I can be guilty of this) have unrealistic expectations for a lens and forget to look back at older lenses (even from the 90's and early 2000's) and realize that they were far from perfect. We also all forget how good a job the combination of 12mpx and a sub-1080p screen did for covering up any imperfections/issues. A lot of my old shots that I thought looked sharp back years ago (and which led me to think I had amazingly sharp lenses), no longer acquit themselves very well.
Again, all that being said, they've done an impressive job and designed/manufactured some really amazing and sharp lenses. This system has been a revelation for me and made me become much more involved in photography. It's also given me a bad case of GAS unlike Nikon or Canon were ever able to do.
p.5 #7 · 24-105mm FOCUS SHIFT survey - FINAL RESULTS
Taff16 wrote:
I would like to add to this debate - I know that the A7R2 camera focuses internally but to be sure I sent my lens 1814471 back to Sony Service Center they reported NO faults with the lens - but there is - as it only focuses in AFC mode.
Did they close the case on that base or you continue to argue with them? I am asking as I fear now the same ...
p.5 #9 · 24-105mm FOCUS SHIFT survey - FINAL RESULTS
snapsy wrote:
One idea that came to mind - is it possible the aperture mechanism/blades are tilted, which wouldn't affect the projection when wide open but would as soon as the blades are stopped down even a little?
I have no idea if this experiment is valid or useful but I got the idea to compare the shift between the lens using its internal aperture vs using an aperture I created using a piece of paper placed in front of the lens Here are the results - look at the circles to the left of the numbers to gauge the focus shift. Notice how the focus shift doesn't occur with the paper aperture.
p.5 #11 · 24-105mm FOCUS SHIFT survey - FINAL RESULTS
Messier77 wrote:
2. Going from 1080p screens to 5k screens likewise exposes issues/imperfections. This also allows a greater proportion of buyers to easily be intensive "pixel peepers,"
This has the opposite effect- for the same size display, more pixels means that pixels are smaller, and 1:1 viewing results in less ability to discern imperfections.
It would however allow for more of the frame to be viewed at 1:1, so an individual with very good vision might be able to still see the imperfections but also have more context for them with a higher resolution display.
p.5 #12 · 24-105mm FOCUS SHIFT survey - FINAL RESULTS
johnctharp wrote:
This has the opposite effect- for the same size display, more pixels means that pixels are smaller, and 1:1 viewing results in less ability to discern imperfections.
It would however allow for more of the frame to be viewed at 1:1, so an individual with very good vision might be able to still see the imperfections but also have more context for them with a higher resolution display.
Perhaps it's more a function of much larger screens being widely and cheaply available. The difference when I moved from a 13.3" 1080p monitor to a 27" 5K monitor was night and day when reviewing my old photos and spotting unsharpness.
p.5 #13 · 24-105mm FOCUS SHIFT survey - FINAL RESULTS
Some information after optically testing the one I have that misfocuses stopped down.
1) Optically, it is identical to the dozen I tested that do not have the problem. Actually the shifter is among the better MTFs wide open, the field curvature is no different, etc. etc. This goes against a true focus shift; you would expect some optical difference if it was a true optical effect.
2) We tested for focus shift in the following manner: Lens is mounted, set at infinity focus by the camera at f/4, and focusing distance measured to within a micron. Then we stop down to f/5.6, f/8, f5.6, and f/4, remeasuring focusing distance each time (to the plane of image focus). Repeat for 24mm, 70mm, and 105mm focal lengths.
Other 24-105s tested this way change focus plane about 0.02mm when stopped down or opened up a stop.
The shifting lens at 24mm, changed 0.02 from f/4 to f5.6, and 0.03 from f5.6 to f/8, so about like the rest.
At 70mm it changed 0.312 from f/4 to f/5.6 and another .135mm from f/5.6 to f/8.
At 105mm it changed .73mm from f/4 to f/5.6. We couldn't measure f/8. It had shifted so far that it was beyond the range of our bench (the bench is working at close distances with mirrorless systems.
My factual conclusion is there's no doubt the shifting problem occurs in some copies and not others. This is an enormous difference.
My opinion is this is not optical focus shift at all but something different. I haven't been inside one, but it has a compensating element and focusing elements which are near the aperture, perhaps even part of the aperture assembly. I suspect stopping down, either from electronic or mechanical reasons, is interfering with the focusing / compensating element spacing in some way.
Right now, I only have a single misfocusing copy and this was a test with methodology not confirmed on multiple samples. So please don't say I found the problem or know what it is. I confirmed what you guys already knew, and said some things I'm pretty sure it isn't.
This has been a wonderful example of constructive forum input at it's best and in that spirit I'll ask a favor of any of you who have a misfocuser in your possession: would you check and see if the problem is there at 24mm? On this copy it wasn't, but was certainly apparent at 35mm.
p.5 #16 · 24-105mm FOCUS SHIFT survey - FINAL RESULTS
Roger, I just figured the best way to get a quality copy of this lens is to rent then buy one of yours! I have an order arriving Friday! Thanks for all this work!
p.5 #18 · 24-105mm FOCUS SHIFT survey - FINAL RESULTS
RCicala wrote:
Some information after optically testing the one I have that misfocuses stopped down.
1) Optically, it is identical to the dozen I tested that do not have the problem. Actually the shifter is among the better MTFs wide open, the field curvature is no different, etc. etc. This goes against a true focus shift; you would expect some optical difference if it was a true optical effect.
2) We tested for focus shift in the following manner: Lens is mounted, set at infinity focus by the camera at f/4, and focusing distance measured to within a micron. Then we stop down to f/5.6, f/8, f5.6, and f/4, remeasuring focusing distance each time (to the plane of image focus). Repeat for 24mm, 70mm, and 105mm focal lengths.
Other 24-105s tested this way change focus plane about 0.02mm when stopped down or opened up a stop.
The shifting lens at 24mm, changed 0.02 from f/4 to f5.6, and 0.03 from f5.6 to f/8, so about like the rest.
At 70mm it changed 0.312 from f/4 to f/5.6 and another .135mm from f/5.6 to f/8.
At 105mm it changed .73mm from f/4 to f/5.6. We couldn't measure f/8. It had shifted so far that it was beyond the range of our bench (the bench is working at close distances with mirrorless systems.
My factual conclusion is there's no doubt the shifting problem occurs in some copies and not others. This is an enormous difference.
My opinion is this is not optical focus shift at all but something different. I haven't been inside one, but it has a compensating element and focusing elements which are near the aperture, perhaps even part of the aperture assembly. I suspect stopping down, either from electronic or mechanical reasons, is interfering with the focusing / compensating element spacing in some way.
Right now, I only have a single misfocusing copy and this was a test with methodology not confirmed on multiple samples. So please don't say I found the problem or know what it is. I confirmed what you guys already knew, and said some things I'm pretty sure it isn't.
This has been a wonderful example of constructive forum input at it's best and in that spirit I'll ask a favor of any of you who have a misfocuser in your possession: would you check and see if the problem is there at 24mm? On this copy it wasn't, but was certainly apparent at 35mm.
Thanks Roger. Do you have any plans to take this copy apart? If your theory turns out to be true I wonder if this is strictly an assembly issue and/or if it's something which can develop over time as well (for copies which currently aren't affected).
p.5 #20 · 24-105mm FOCUS SHIFT survey - FINAL RESULTS
snapsy wrote:
Thanks Roger. Do you have any plans to take this copy apart? If your theory turns out to be true I wonder if this is strictly an assembly issue and/or if it's something which can develop over time as well (for copies which currently aren't affected).
This is a concern I have as well, as I'm right in the middle of the bad batch it seems.
Here are the results - look at the circles to the left of the numbers to gauge the focus shift. Notice how the focus shift doesn't occur with the paper aperture.