SL sensor glass thickness

[chrismuc]

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Acc. Diglloyd, Leica M has thinnest sensor glass, Leica SL thicker and Panasonic S1R thickest (Sony even thicker …).

So, as we know, Leica M lenses only can work best on Leica M cameras.

But what I find pretty counterproductive is: two cameras with Leica L mount use different sensor glass thicknesses? How then a Panasonic (or Sigma) lens shall work ‘perfectly’ on a Leica SL camera and how should a Leica L mount lens should work ‘as advertised’ on a Panasonic L mount camera? Shouldn’t the sensor glass thickness - obviously - be part of a mount definition? 

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[BernardC]

1 hour ago, chrismuc said:

But what I find pretty counterproductive is: two cameras with Leica L mount use different sensor glass thicknesses? How then a Panasonic (or Sigma) lens shall work ‘perfectly’ on a Leica SL camera and how should a Leica L mount lens should work ‘as advertised’ on a Panasonic L mount camera? Shouldn’t the sensor glass thickness - obviously - be part of a mount definition? 

I suspect that the L-Mount specifications allow for a range of sensor glass thickness, and that Leica is at the short end of that range. That shouldn't be an issue, sensor glass thickness isn't as critical with digital-era (near-telecentric) lenses. Leica is the only L-Mount partner that officially supports M lenses, so they are the only one that needs to worry about this.

Having a range of glass thickness and back-focus within one lens mount isn't unusual. There was a LensRentals blog a few years back that compared back-focus across different cameras and found that it varied among models of the same brand. Part 2 is here, with a link to part 1 at the top.

Sensor thickness only affects sensor-to-flange distance for telecentric lenses, because all the light from the lens reaches the sensor glass at (nearly) the same angle. The "problem" with some film-era lenses is that light could hit the film plane at an extreme angle, which wasn't a concern with film.

[beewee]

Sensor glass mainly come into play when light rays from the lens hit the sensor at a shallow angle, particularly near the edge/corner, as oppose to hitting the sensor at a perpendicular angle. The L-mount lenses are close to tele-centric which means that the light rays hit the sensor at a perpendicular angle (#4 below) whereas M-lenses are not tele-centric in the image space (#2 below) and are susceptible aberrations caused by a thick sensor glass.

This is why M-lenses work best on M cameras. M-lenses work ok (not great) on SL cameras, and perform worst on most third-party cameras that have thicker cover glass.

 

 

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Edited August 30, 2021 by beewee

[AZN]

4 hours ago, beewee said:

M-lenses work ok (not great) on SL cameras

Ahem… some M-lenses have issues.  Others work fine, brilliantly even.

The LEICA ELMAR-M 24 f/3.8 ASPH (which I have used for years now) is a pig's breakfast on Sony R cameras (have tried it on the 7AR, 7ARII and 7ARIV).  On the SL (Typ-601) it is corner to corner sharp with no colour shift in the corners.

The LEICA SUMMICRON-M 35mm f/2 ASPH also struggles on the Sonys, not as bad as the 24mm, but still is mud in the corners.  OTOH it is "perfect" on the SL (Typ-601)

Unsurprisingly, longer focal length M lenses all work without problems.  At least the ones I have used.

Maybe ultra-wide M lenses struggle.  Also maybe the 28mm M-Elmarit?  Don't know, cannot say.  But the wides I list above work obsessive-pixel-peeper fine. 😀

Edited August 30, 2021 by AZN

[beewee]

Interesting that you point out the 24 Elmar working well on the SL. It doesn’t play nice with the SL2-S. It’s amazing on the M10.

Yes, I should have qualified that some M lenses works fine on the SL, mostly 50+mm plus and specifically the 35 APO ASPH works very well.

I haven’t been happy with any of my wide angle M lenses (18 SEM, 24 Elmar, 28 Elmarit ASPH v1) on the SL2-S and pretty much gave up with M lenses on the SL2-S.

[jaapv]

I think This article explains the question well.  The performance issue is more in the microlenses and physical pixel size than in the sensor glass thickness. That particular Internet Issue stems from the time that sensors had (and some still have) thick AA filters. AFAIK none of the cameras mentioned have an AA filter. The only filter that could make a difference here is the IR filter, and that has been discussed ad nauseam since the M8. The problem there is colour shift, not sharpness.

[easy_action]

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On 8/31/2021 at 10:47 AM, jaapv said:

I think This article explains the question well.

Unless I missed it, there doesn't appear to be any confirmation in the article that the M microlens design is also used in the SL.

[jaapv]

Read again - nobody claims that the microlens design of the SL is the same as the M. The M does not have to work with L lenses. The SL has a different way of accommodating M lenses: parabolic microlenses. The M uses shifted microlenses. 

[easy_action]

The section on parabolic microlenses was previously published on the same blog in January 2016: https://gmpphoto.blogspot.com/2016/01/the-future-of-sensor-technology-at-leica.html

The diagram comparing standard and parabolic microlenses is even older - post 13 in this thread from 2012 shows the exact same https://www.l-camera-forum.com/topic/188258-leica-m-microlenses/

This 2012 discussion seems to present the parabolic design as a feature of the M sensor.

 

[easy_action]

I wonder if both the SL and M sensors make use of parabolic microlenses, but in addition the M also has offset ('shifted') microlenses to improve performance with film era wide angles.

Does this explain why the SL series are much better with M mount lenses than other mirrorless cameras, but still not as good as M digitial bodies?

[Malabito]

On 8/31/2021 at 2:35 AM, beewee said:

Interesting that you point out the 24 Elmar working well on the SL. It doesn’t play nice with the SL2-S. It’s amazing on the M10.

Yes, I should have qualified that some M lenses works fine on the SL, mostly 50+mm plus and specifically the 35 APO ASPH works very well.

I haven’t been happy with any of my wide angle M lenses (18 SEM, 24 Elmar, 28 Elmarit ASPH v1) on the SL2-S and pretty much gave up with M lenses on the SL2-S.

Hi I just got the sls2 and also have a 24mm f3.8, won't be able to test the combination since I am traveling,  but I am curious to know of why you say it's horrible on the sls2?

That lens actually worked quite good on the Panasonic s1, some weird color cast If you shot on a sunny day, (could be corrected), but it was sharp almost almost all thw way to the corners, very little smearing, I was expediting it to work better on the sls2. 

Edited October 9, 2021 by Malabito

[LBJ2]

On 8/30/2021 at 12:10 PM, BernardC said:

I suspect that the L-Mount specifications allow for a range of sensor glass thickness, and that Leica is at the short end of that range. That shouldn't be an issue, sensor glass thickness isn't as critical with digital-era (near-telecentric) lenses. Leica is the only L-Mount partner that officially supports M lenses, so they are the only one that needs to worry about this.

Having a range of glass thickness and back-focus within one lens mount isn't unusual. There was a LensRentals blog a few years back that compared back-focus across different cameras and found that it varied among models of the same brand. Part 2 is here, with a link to part 1 at the top.

Sensor thickness only affects sensor-to-flange distance for telecentric lenses, because all the light from the lens reaches the sensor glass at (nearly) the same angle. The "problem" with some film-era lenses is that light could hit the film plane at an extreme angle, which wasn't a concern with film.

Probably one of the most well balanced and practical responses I've seen on this topic 👍

[beewee]

12 hours ago, Malabito said:

Hi I just got the sls2 and also have a 24mm f3.8, won't be able to test the combination since I am traveling,  but I am curious to know of why you say it's horrible on the sls2?

That lens actually worked quite good on the Panasonic s1, some weird color cast If you shot on a sunny day, (could be corrected), but it was sharp almost almost all thw way to the corners, very little smearing, I was expediting it to work better on the sls2. 

The 24mm f/3.8 isn’t terrible on the SL2-S per say, but it doesn’t shine like it does on an M body. The Sigma 24/3.5 DG DN performs better in the corners on the SL2-S than the 24/3.8 M and it’s 1/5th the price. So to put thing in perspective, I wouldn’t purchase a the Leica 24/3.8 M if I wasn’t planning to shoot with it with an M body. On the other hand, you can probably get by with the 24/3.8 on the SL2-S if you already have one but you’d be better served with the better performing Sigma 24/3.5 DG DN and if you have no intention of going back to an M body, then you’d be better served selling the 24/3.8 M if you can sell it at a good price.

All that being said, the 24/3.8 M is not a bad lens at all. Until the 24 APO SL is released, it continues to be the sharpest and best performing 24mm lens Leica has ever made, if used on an M body with an M sensor. The same cannot be said if used on the SL bodies.

Edited October 9, 2021 by beewee

[Malabito]

8 hours ago, beewee said:

The 24mm f/3.8 isn’t terrible on the SL2-S per say, but it doesn’t shine like it does on an M body. The Sigma 24/3.5 DG DN performs better in the corners on the SL2-S than the 24/3.8 M and it’s 1/5th the price. So to put thing in perspective, I wouldn’t purchase a the Leica 24/3.8 M if I wasn’t planning to shoot with it with an M body. On the other hand, you can probably get by with the 24/3.8 on the SL2-S if you already have one but you’d be better served with the better performing Sigma 24/3.5 DG DN and if you have no intention of going back to an M body, then you’d be better served selling the 24/3.8 M if you can sell it at a good price.

All that being said, the 24/3.8 M is not a bad lens at all. Until the 24 APO SL is released, it continues to be the sharpest and best performing 24mm lens Leica has ever made, if used on an M body with an M sensor. The same cannot be said if used on the SL bodies.

thanks for the clarifications. I have the lens cause i use it on the m10, (before an m240) and you are right is an amazing lens. I will be using it also in the sls2 since i have both systems m and sl. But my plan is to buy the sigma 24mm f2.0 when it becomes available locally.

Have you tested the sigma 24mm f2.0? I can get the sigma f3.5 for cheap  but given i do portraits with 24mm the f2.0 aperture really makes me want the f2.0 version. 

 

[beewee]

9 hours ago, Malabito said:

thanks for the clarifications. I have the lens cause i use it on the m10, (before an m240) and you are right is an amazing lens. I will be using it also in the sls2 since i have both systems m and sl. But my plan is to buy the sigma 24mm f2.0 when it becomes available locally.

Have you tested the sigma 24mm f2.0? I can get the sigma f3.5 for cheap  but given i do portraits with 24mm the f2.0 aperture really makes me want the f2.0 version. 

 

I haven’t tried the Sigma 24/2 but initial samples look pretty good and the mtf charts are comparable to the f/3.5 version which is impressive. I mostly got the 24/3.5 due to it’s combination of size, weight, and optical performance when stopped down slightly to f/5.6-8 as a light weight landscape lens. I’ll probably get the 21 and 24 APO SL when they eventually becomes available for the times when I’m willing to carry more weight to achieve maximum performance wide open and want to achieve a certain look. The 28 APO SL is stunning.

 Weight is a big consideration for me since I mostly use them SL system in the mountains while hiking and scrambling.