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...
jaapv
RFF Sponsoring Member.
There is indeed a difference. I insert two quotes from earlier threads (making this quit a long answer- sorry...)
)
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jvr
Well-known
Yep!
Thanks for the info!
That really makes sense.
Thanks for the info!
That really makes sense.
wintoid
Back to film
I'm very interested by what you say because I've felt something similar myself. However, I do think you're making a jump between saying that the M3 focuses fine vs the RD1s and then inferring that it's due to film vs digital. For example, it could be caused by the fact that the focusing components of the lens/body don't line up so well with the RD1s as with the M3, or something like that.
Having said that, what you say matches my own feelings. As documented in another recent thread, my R2a seems to focus lenses just fine where the RD1s does not. Although I am at the stage of doubting my own feelings, it's interesting that my impressions would seem to match yours.
Having said that, what you say matches my own feelings. As documented in another recent thread, my R2a seems to focus lenses just fine where the RD1s does not. Although I am at the stage of doubting my own feelings, it's interesting that my impressions would seem to match yours.
pvdhaar
Peter
Yeah, I know what you mean.. I've seen the same difference between an F75 and a D50 both equiped with the same AF sensor. On the F75, the 50mm lens shines, and is always sharp. On the D50, it's a hit/miss thing.
When it's focused good, it's really good.. and I mean really really good. Beating the F75 hands down. But 80% of the time, it's not quite there. Fuzzier than the F75 whose results appear 100%consistent..
I guess the main culprit is the required magnification ratio for enlargements to a given size. A more precise focusing mechanism in case of a digital crop factor seems to be needed to get consistent results again..
But I wouldn't rule out the possibility that differences between lenses also play a part. I've got a 28-70/3.5-4.5 that works like a charm on the DSLR, while it's so-so on the F75. Which is entirely the other way round as it were..
When it's focused good, it's really good.. and I mean really really good. Beating the F75 hands down. But 80% of the time, it's not quite there. Fuzzier than the F75 whose results appear 100%consistent..
I guess the main culprit is the required magnification ratio for enlargements to a given size. A more precise focusing mechanism in case of a digital crop factor seems to be needed to get consistent results again..
But I wouldn't rule out the possibility that differences between lenses also play a part. I've got a 28-70/3.5-4.5 that works like a charm on the DSLR, while it's so-so on the F75. Which is entirely the other way round as it were..
jaapv
RFF Sponsoring Member.
jvr (what is your first name btw? ) makes a very good point about field curvature (it can even produce a wavy plane of focus) and film curvature. That will influence your focussing considerably, depending on spot you focus on. Eliminate one ( the film) and the whole situation changes.
) makes a very good point about field curvature (it can even produce a wavy plane of focus) and film curvature. That will influence your focussing considerably, depending on spot you focus on. Eliminate one ( the film) and the whole situation changes.pfogle
Well-known
this (field curvature) is particularly true of wide aperture lenses, which may well be optimised for either central sharpness, or for a 'ring' of sharpness to give a more overall impression of a sharp image.jaapv said:jvr (what is your first name btw?
Of course, this will be more of a problem for an RF camera, where you cannot asses the focus visually, compared to a reflex camera, where either you or the AF will do the focusing by looking at the image on the screen.
The ruler test will not work well with a curved field of focus, as the rangefinder spot may not be in the region of sharpest focus, and the ruler won't show it up. You'd have to supplement this with a shot of, say, a newspaper flat on a wall, to see if the focus is out (or in!) evenly across the frame.
wintoid
Back to film
ferider said:
Ooh that's interesting too. It just makes life even harder of course.
Finder
Veteran
What you need to consider is depth of FOCUS (the zone in front and behind the image plane that would result in a "sharp" image), which is dependant on the effective aperture in use rather than the focal length - at f/8 all lenses have the same depth of focus. When calculating depth of focus, you need to determine the permissable circle of confusion. Obviously, the smaller the format, the smaller the permissible circle of confusion. Also, the higher the pixel resolution for a given size sensor, the greater need for tighter circles of confusion. Basically, your Epson is more sensitive to fuzzines than a 35mm camera.
BTW, film flatness is not really the issue as the film surface is randomly uneven rather than in a bowl shape curve that may possibly coincide with a curved image plane.
BTW, film flatness is not really the issue as the film surface is randomly uneven rather than in a bowl shape curve that may possibly coincide with a curved image plane.
Finder
Veteran
BTW, depth of focus determines the tolerances for an entire system. The focusing system, either the rangefinder or focusing screen, must also fall within those tolerances.