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I’m no expert in the physics involved but optimising a lens design for a digital platform is different to film use. This isn’t part of why epic lens manufacturers from the film era, Leica and Hasselblad took in outside help with lens design and production when they entered the digital world. 
 

And then again, lots of us are using and loving old glass on our digital M cameras and others. This tells me ‘it’s complicated’ 

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With film the light rays are straight into the film and the lenses were designed accordingly.

Digital cameras have a cover glass over the sensor which causes the light to bend/refract some more. This extra refraction causes a reduction sharpness compared to a lens designed with a digital sensor in mind. 

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Really only an issue with wider angle rangefinder lenses where the light rays reaching the edges of the sensor are at a significant angle. A digital sensor is not like film where the angle of light rays don't have much effect. a digital sensor may have more vignetting and color shifts as the ray angles get significant. I only see a significant effect with some lenses 35mm & wider, especially with a older 21mm lens. There is some effect at 50 mm on some sensors. The effects lessen with more modern sensor designs: the M10 is better than the 240, and the M10-R a major improvement. I see the most effect on other mirrorless makes like Sony A7 where the sensor "stack" is thicker and smears the sides and edges more. Even there I've had good pictures with 35mm RF lenses on Sony A7.

Edited by TomB_tx
typo
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6 minutes ago, TomB_tx said:

The effects lessen with more modern sensor designs: the M10 is better than the 240

This is something I’ve always wondered. Is the 24mp in the M10 a different sensor to the 24mp in the 240 variants? Or is it the same chip but with different filters, glass and processing? 

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1 hour ago, kiwidad said:

If the sensor on a Digital leica is the same distance from the mount as the film plane what exactly is there to "adapt" to digital on a lens?? This sounds like hogwash to me!

There is no adaptor needed between film and digital. With a very few exceptions (very wide angle) Leica M lenses will work with film and digital.

My 21/2.8 Elmarit M works perfectly on my M-P 240 and my M2.

Ernst

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Reading the replies… so if someone says they modified a lens for digital it’s hogwash

I get the angle of light striking the sensor matters dues to the glass cover thicknet and I think that’s the design aspect. 
 

I saw images shot on m10 and m11 with a super angulon and the m10 had a color cast on edges. Suggests the m11 may not need the radical lens redesigns other leicas and brands need in the glass!

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1 hour ago, Dazzajl said:

This is something I’ve always wondered. Is the 24mp in the M10 a different sensor to the 24mp in the 240 variants? Or is it the same chip but with different filters, glass and processing? 

And the issues are almost totally gone on the m11!

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Digital is less forgiving for misfocus, don't ask me why. 2 of my film lenses that suffered from back or front focus have been calibrated for digital by Leica: Elmarit 90/2.8 v2 and Summicron 90/2 v3. I've heard also about early Summicron 35/2 asph v1's that were more prone to focus shift that my digital copy. JFI.

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1 hour ago, kiwidad said:

Reading the replies… so if someone says they modified a lens for digital it’s hogwash

I get the angle of light striking the sensor matters dues to the glass cover thicknet and I think that’s the design aspect. 
 

I saw images shot on m10 and m11 with a super angulon and the m10 had a color cast on edges. Suggests the m11 may not need the radical lens redesigns other leicas and brands need in the glass!

Manufacturers have over the last decades tried to get to a more telecentric design indeed. But typically, these then were redesigns with new names and typicalls resulted in much larger lenses. The sensor on M cameras have y special Microlens array to compensate for their non-telecentric design and those Microlenses are indeed different from one model to another.

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1 hour ago, kiwidad said:

I saw images shot on m10 and m11 with a super angulon and the m10 had a color cast on edges. Suggests the m11 may not need the radical lens redesigns other leicas and brands need in the glass!

As far as color shift is concened, M11 and other cameras with BSI sensors are indeed superior to earlier digital cameras, especially with WA and UWA lenses. Here S-A 21/3.4 on M11 and M240:

https://photos.smugmug.com/Diverse/n-QFBj4/Leica-M11-Leica-2134/i-7HHRPwp/0/Lnfp577zbFFmfsStvZKDx9wmLMKWmkWZ4qGmrnLGN/X4/M1002785_si-X4.jpg

https://photos.smugmug.com/Diverse/n-QFBj4/Leica-M11-Leica-2134/i-66CG5w6/1/KSTKMd2GKZSKVxVZCs9NCp5nvzJrMMwqXCghg9MwZ/X4/M2401767_si-X4.jpg

 

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13 minutes ago, kiwidad said:

What stricter requirements?

As @lct said, digital is less forgiving for misfocus. Film has a certain softness due to the nature of the emulsion and grain structure, which can mask minor miscalibrations. Film has a natural depth to its emulsion layers, which can create a slight "forgiving" effect on focus errors. Digital sensors, being flat and extremely precise, demand perfect focus. Even small misalignments become noticeable.

Edited by evikne
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Posted (edited)

Even though the explanation of the „natural depth“ of the film emulsion is right, much more important is how we look at the results of photography with film and with a digital sensor. With film it takes at least some hours until you see the results - usually days or weeks. You don‘t remember how exact your focus was when you took the photo. The results from a digital sensor are available immediately and can be compared much easier than with film. Who ever looked at his photos with film with a magnification that equals a 100 or 200% magnification by his software on a screen with a distance of less than a meter?

That‘s the true reason why digital photography is much less forgiving. Older lens designs which for example showed focus shift did so already with film, but people didn’t notice it or lived with it. With digital photography people started to notice the fault and complained, so the lensmakers had to react and find ways to avoid focus shift. Or they used smaller tolerances for calibration, or used lens designs which made the light hit the sensor in less flat angles etc.

The „adaptation for digital“ is an adaptation to less forgiving customers who use digital photography.  

 

Edited by UliWer
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I purchased a lens a while back that was supposedly "optimized for digital".  The only difference that I noticed was that it was 6 bit coded.  It works well on my m10r as well as my m3.  Did they make any changes to the focus, I don't know.  It works well on both cameras so I kind of have my doubts about any real optimization for digital other than the 6 bit thing.  But hey, it's a good selling point to convince people to upgrade their lenses.  Maybe you're not too far off with the "hogwash" thing. But then maybe because it's a 24mm I just haven't noticed any real difference.

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This is the way my Elmarit 90 misfocused until i had it calibrated for digital. Worked fine with film, don't ask me why.

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19 hours ago, Dazzajl said:

This is something I’ve always wondered. Is the 24mp in the M10 a different sensor to the 24mp in the 240 variants? Or is it the same chip but with different filters, glass and processing? 

Yes

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16 hours ago, evikne said:

As @lct said, digital is less forgiving for misfocus. Film has a certain softness due to the nature of the emulsion and grain structure, which can mask minor miscalibrations. Film has a natural depth to its emulsion layers, which can create a slight "forgiving" effect on focus errors. Digital sensors, being flat and extremely precise, demand perfect focus. Even small misalignments become noticeable.

So you telling me Leica were sloppy with calibration of the rangefinder on film cameras?
yeah not running with that myself?

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Posted (edited)
13 hours ago, lct said:

This is the way my Elmarit 90 misfocused until i had it calibrated for digital. Worked fine with film, don't ask me why.

 

i think that’s is a straight up manufacturing flaw and not alignment. That’s a massive backfocus!

my Elmarit-m 90 arrives next week and if it focuses that bad it going back!

Edited by kiwidad
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