jvr
Well-known
Hi!
I guess everyone is fed up with Epson RD-1 misfocus thereads. But I'm a very curious person and I've been having very puzzling results, regarding bad focusing with some lenses, on my RD-1s. My puzzlement comes from combining 2 facts:
1) Some "easier" to focus lens (such as the Leica 35/3.5 Summaron) were showing worse focus than "hard" to focus (such as the CV Nokton 50/1.5 wide-open).
2) The results are not consistent between the RD-1s and my M3. This means that two lenses can be great on the M3 but one of them back/front focus badly on the RD-1s.
I've had my share of tripod+45deg ruler test (I can post some pics), especially after my Epson's rangefinder became misaligned, both vertically and (worse) horizontally. I was able to adjust it horizontally, thanks to very detailed instructions from poeple on this forum (thank you!) but not vertically (strange, because that's the big screw and it should work easily... 🙁 ).
I decided to use precisely the CV 35/2.5 to align it on infinity, because it has a direct M mount - so no adapter thickness issues - and also because all my Leica lenses are old - so probably have worse tolerances.
After RF alignment, all my CV lenses (except for the 35/1.2 Nokton which I bought a couple of weeks ago, not even yet on my signature... 🙂 ) focus ok on the Epson, including those that use adapters. Not "perfect" but more than enough for real life pictures and even some pixel-peeping 🙂. The Leica lenses remain the same: the 90/4 elmar is ok, the 50 col. summicron is ok, the 35 summaron still backfocus noticeably.
Now, for the fun part. 🙂
On my Leica M3 I don't see any _real_ focus problem. Even with the 35/1.2 Nokton (that focus badly enough on the Epson that I'll probably have it collimated, as I would like to use at 1.2 and DOF is almost 0) and the 35/3.5 Summaron (that back-focus almost 10 cm at 3m on the Epson). My tests used the same setup (ruler+tripod) and TMAX 100+XTOL, scanned on a Nikon LS-4000ED. Again, it's not that focus is "perfect". But it seems that the film process tolerates much better small focusing innacuracies.
Although I reapeated the tests enough times to be almost sure that accuracy of focus was not the issue, it's true that the Leica has a longer RF base and _could_ be more accurate when focusing (especially the M3, with a large magnification RF). But my M3 is 50 years old and the finder is a bit dimmer than the Epson, etc...
Moreover, and IMHO, the (theoretical) focus accuracy advantage of the M3 does not explain the differences because the issues are very consistent, not random. Ie, it always happens with the same lenses and in the same way - the Summaron never focus ok on the Epson and always back-focus, for example.
So, it really looks like the film process has some different properties that make it more "tolerant" to small misfocus.
I felt exactly the same when I switched from film SLRs to digital SLRs (at the time, a Nikon D100). I don't remember having so many "just slightly out-of-focus" pictures on film. On the other hand, and to be honest, I've never had pictures so sharp when they were in focus. I quickly realized that accurate focus is a _must_ for digital and easily the worst offender. Some of my lenses were so-so regarding focus on the D100 and that just didn't cut it on digital, so I dumped them. All of them worked ok on the F-801s, at least were not "offensive".
The only explanations I have for this is that
1) the film has some thickness and
2) can be (usaully is) curved
while the sensor surface has almost zero thickness and is flat.
Film curvature could help lenses that show field curvature (very common on fast lenses, such as the CV 35/1.2 Nokton) and film thickness can "adjust" to less than perfect focus: when we print or scan the film we will use the plan of better contrast in the film to focus and that could be different (and usually is) from the surface.
Anyone with ideas? Just out of curiosity, nothing else...😛
I guess everyone is fed up with Epson RD-1 misfocus thereads. But I'm a very curious person and I've been having very puzzling results, regarding bad focusing with some lenses, on my RD-1s. My puzzlement comes from combining 2 facts:
1) Some "easier" to focus lens (such as the Leica 35/3.5 Summaron) were showing worse focus than "hard" to focus (such as the CV Nokton 50/1.5 wide-open).
2) The results are not consistent between the RD-1s and my M3. This means that two lenses can be great on the M3 but one of them back/front focus badly on the RD-1s.
I've had my share of tripod+45deg ruler test (I can post some pics), especially after my Epson's rangefinder became misaligned, both vertically and (worse) horizontally. I was able to adjust it horizontally, thanks to very detailed instructions from poeple on this forum (thank you!) but not vertically (strange, because that's the big screw and it should work easily... 🙁 ).
I decided to use precisely the CV 35/2.5 to align it on infinity, because it has a direct M mount - so no adapter thickness issues - and also because all my Leica lenses are old - so probably have worse tolerances.
After RF alignment, all my CV lenses (except for the 35/1.2 Nokton which I bought a couple of weeks ago, not even yet on my signature... 🙂 ) focus ok on the Epson, including those that use adapters. Not "perfect" but more than enough for real life pictures and even some pixel-peeping 🙂. The Leica lenses remain the same: the 90/4 elmar is ok, the 50 col. summicron is ok, the 35 summaron still backfocus noticeably.
Now, for the fun part. 🙂
On my Leica M3 I don't see any _real_ focus problem. Even with the 35/1.2 Nokton (that focus badly enough on the Epson that I'll probably have it collimated, as I would like to use at 1.2 and DOF is almost 0) and the 35/3.5 Summaron (that back-focus almost 10 cm at 3m on the Epson). My tests used the same setup (ruler+tripod) and TMAX 100+XTOL, scanned on a Nikon LS-4000ED. Again, it's not that focus is "perfect". But it seems that the film process tolerates much better small focusing innacuracies.
Although I reapeated the tests enough times to be almost sure that accuracy of focus was not the issue, it's true that the Leica has a longer RF base and _could_ be more accurate when focusing (especially the M3, with a large magnification RF). But my M3 is 50 years old and the finder is a bit dimmer than the Epson, etc...
Moreover, and IMHO, the (theoretical) focus accuracy advantage of the M3 does not explain the differences because the issues are very consistent, not random. Ie, it always happens with the same lenses and in the same way - the Summaron never focus ok on the Epson and always back-focus, for example.
So, it really looks like the film process has some different properties that make it more "tolerant" to small misfocus.
I felt exactly the same when I switched from film SLRs to digital SLRs (at the time, a Nikon D100). I don't remember having so many "just slightly out-of-focus" pictures on film. On the other hand, and to be honest, I've never had pictures so sharp when they were in focus. I quickly realized that accurate focus is a _must_ for digital and easily the worst offender. Some of my lenses were so-so regarding focus on the D100 and that just didn't cut it on digital, so I dumped them. All of them worked ok on the F-801s, at least were not "offensive".
The only explanations I have for this is that
1) the film has some thickness and
2) can be (usaully is) curved
while the sensor surface has almost zero thickness and is flat.
Film curvature could help lenses that show field curvature (very common on fast lenses, such as the CV 35/1.2 Nokton) and film thickness can "adjust" to less than perfect focus: when we print or scan the film we will use the plan of better contrast in the film to focus and that could be different (and usually is) from the surface.
Anyone with ideas? Just out of curiosity, nothing else...😛
