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SL vs 240 with UWA and WA


uhoh7

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All the Leica wides perform well except the summicron 28/2 and 35/2 where corner performance is a fair bit worse than the M240.

 

The more modern designs are as good if not better on the SL. 

 

There are a few threads from december that show examples and compare them if you care to search .....

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I think what Charlie is asking is whether they work better on the M240 or not as well on the SL, and the right answer would be, they work better on the M except for the 28 lux, even though they mostly work well enough on the SL.

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I'm not so sure Edward. Especially the new versions of the 28 cron, 28 elmarit, and 35 cron have not been tested on the M240 vs the SL as far as I know. If there have been tests, I would love to see them. The 18 SEM and 21 SEM seem to be slightly better on the M240, but it seems to be almost only at close distances and wide open (not the typical use case for these lenses for most people). The WATE, the 21 lux, the 24 lux, seem to perform almost exactly the same on the two cameras, which makes sense as these three have longer exist pupils. The 24 Elmar ASPH seems somewhere in between the 18 and 21 SEM and the 24 Lux. Perhaps just a shade better wide ope at close distance on the M240, but there doesn't seem to be much to it. The 35 Lux FLE also seems very similar on the two cameras. The 28 Lux seems to be slightly better on the SL. Now, if you are talking older lenses that aren't available new, then they all do tend to perform a bit to a lot better on the M240, but the ones currently available the few differences are small and for one lens (the 28 lux) the advantage is actually for the SL.

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I'm not so sure Edward. Especially the new versions of the 28 cron, 28 elmarit, and 35 cron have not been tested on the M240 vs the SL as far as I know. If there have been tests, I would love to see them. The 18 SEM and 21 SEM seem to be slightly better on the M240, but it seems to be almost only at close distances and wide open (not the typical use case for these lenses for most people). The WATE, the 21 lux, the 24 lux, seem to perform almost exactly the same on the two cameras, which makes sense as these three have longer exist pupils. The 24 Elmar ASPH seems somewhere in between the 18 and 21 SEM and the 24 Lux. Perhaps just a shade better wide ope at close distance on the M240, but there doesn't seem to be much to it. The 35 Lux FLE also seems very similar on the two cameras. The 28 Lux seems to be slightly better on the SL. Now, if you are talking older lenses that aren't available new, then they all do tend to perform a bit to a lot better on the M240, but the ones currently available the few differences are small and for one lens (the 28 lux) the advantage is actually for the SL.

From what I understand, every time there is a small advantage for the M at close range, it gets even clearer at infinity. I can see more field curvature on all my lenses. I can also see a change in the bokeh character too, in the image periphery, which I blame on astigmatism. So it's not only about sharpness. This said, I find the advantages of shooting the SL outweigh by fair any corner weakness issues.

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From what I understand, every time there is a small advantage for the M at close range, it gets even clearer at infinity. I can see more field curvature on all my lenses. I can also see a change in the bokeh character too, in the image periphery, which I blame on astigmatism. So it's not only about sharpness. This said, I find the advantages of shooting the SL outweigh by fair any corner weakness issues.

 

Well you have both cameras to compare and I trust your judgment, but it seems to me that Leica is tweaking the lenses to work better with the thicker cover glass of the SL. That certainly seems true for the 28 lux, and I wonder if it isn't true for the new revision of the 28 cron, 28 elmarit, and 35 cron. I don't think hardly anyone has got their hands on those yet, however, so we will have to wait and see if they are more optimized for the SL than the M240. If they are, then I would guess that the new M will have a bit thicker cover glass and Leica will gradually move all the currently available lenses to be optimized for the thicker cover glass.

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Especially the new versions of the 28 cron, 28 elmarit, and 35 cron have not been tested on the M240 vs the SL as far as I know.

 

 

The new vs previous 28Elmarit has been tested on M240 and SL here (and in the following posts of that thread).

Edited by helged
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Well you have both cameras to compare and I trust your judgment, but it seems to me that Leica is tweaking the lenses to work better with the thicker cover glass of the SL. That certainly seems true for the 28 lux, and I wonder if it isn't true for the new revision of the 28 cron, 28 elmarit, and 35 cron. I don't think hardly anyone has got their hands on those yet, however, so we will have to wait and see if they are more optimized for the SL than the M240. If they are, then I would guess that the new M will have a bit thicker cover glass and Leica will gradually move all the currently available lenses to be optimized for the thicker cover glass.

 

 

It would make perfect sense for Leica to optimize sensors to match the lenses available for a particular mount but less sense to optimize lenses for a particular sensor. Why? Because lenses tend stick around a long time and bodies/sensors change frequently. 

 

However, anything that straightens out the light path to the corners and edges of the frame, making it more orthogonal to the image plane, improves performance on ANY sensor, whether M or SL, thick or thin sensor stack. If the more recent lens designs have been designed with this in mind, they work better on any sensor. 

Edited by ramarren
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I do believe, as mentioned by Steve, that Leica has decided to adopt an SL like sensor on the next M, hence the tweaking of the lenses. It's interesting in the linked comparison that the tweaks make almost no difference on the M and a huge difference on the SL. Being M mount lenses, I see no reason why would Leica tweak them for the SL sensor while they make no difference on the M, unless Leica is planning to standardize its cover glass thickness between the two mounts.

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I do believe, as mentioned by Steve, that Leica has decided to adopt an SL like sensor on the next M, hence the tweaking of the lenses. It's interesting in the linked comparison that the tweaks make almost no difference on the M and a huge difference on the SL. Being M mount lenses, I see no reason why would Leica tweak them for the SL sensor while they make no difference on the M, unless Leica is planning to standardize its cover glass thickness between the two mounts.

 

 

If they're tweaking anything in the lenses, the end result is that the light path is more orthogonal to the imaging plane without cutting down on the imaging qualities of the lens because this improves their performance on any digital sensor and does nothing to hurt their performance on film. 

 

The M sensor was custom-designed to manage short-register M-mount lenses specifically because there are many M mount lenses with a non-optimal ray trace for a digital sensor. It makes perfect sense, if you're redesigning lenses now with digital sensors in mind, that you would make the design changes that enable the lenses to image better on any sensor. 

 

It does not make sense to extrapolate that the next M sensor will have the same cover glass thickness that the current SL sensor does, implying that performance with older, sub-optimal lenses will further degrade, unless you also believe that Leica no longer cares that the older lenses for the M matter. I don't believe that to be the case, personally. On the other hand, if Leica can optimize the SL to handle older lenses as well or better than the M does now, then there's no reason for Leica not to use that sensor in the M line as well. 

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I think you are missing a point. Yes, it is true that moving the exit pupil further from the sensor will reduce the impact of the cover glass of any sensor and could potentially improve the performance on any camera. There is a down side of this strategy, however. The lens will get longer and generally larger. There is another option available to lens designers who want to deal with the astigmatism generated by the cover glass. The designer can adjust the astigmatism of the lens to counteract the astigmatism of the cover glass. This can be modelled by including the properties of the cover glass as part of the optical formula when designing the lens. Designers have to deal with astigmatism caused by the various elements all the time in an optical design and if you think of the cover glass as just another element, then its effect can be modelled and dealt with. This too is a reasonable strategy to account for the effect of the cover glass.

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I think you are missing a point. Yes, it is true that moving the exit pupil further from the sensor will reduce the impact of the cover glass of any sensor and could potentially improve the performance on any camera. There is a down side of this strategy, however. The lens will get longer and generally larger. There is another option available to lens designers who want to deal with the astigmatism generated by the cover glass. The designer can adjust the astigmatism of the lens to counteract the astigmatism of the cover glass. This can be modelled by including the properties of the cover glass as part of the optical formula when designing the lens. Designers have to deal with astigmatism caused by the various elements all the time in an optical design and if you think of the cover glass as just another element, then its effect can be modelled and dealt with. This too is a reasonable strategy to account for the effect of the cover glass.

 

 

I don't know whom you're considering to be missing a point. 

 

However, considering the cover glass to be part of the lens optical formula locks you into one design of cover glass no matter what sensor you're using. Unless you're designing lenses for fixed lens cameras, it's a bad idea to do that because, as said before, lenses stick around for a while (particularly Leica M lenses!) and bodies/sensors come and go. 

 

I strongly doubt Leica would ever use such a lens design tactic for an M or SL lens. It is simply too limiting in the long run, what with new sensors and new sensor technology appearing on a regular basis every year. Leica owners are used to buying lenses which remain viable and useful for generations, not until the next new sensor design arrives, and I'm sure Leica understands that. 

Edited by ramarren
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I don't know whom you're considering to be missing a point. 

 

However, considering the cover glass to be part of the lens optical formula locks you into one design of cover glass no matter what sensor you're using. Unless you're designing lenses for fixed lens cameras, it's a bad idea to do that because, as said before, lenses stick around for a while (particularly Leica M lenses!) and bodies/sensors come and go. 

 

I strongly doubt Leica would ever use such a lens design tactic for an M or SL lens. It is simply too limiting in the long run, what with new sensors and new sensor technology appearing on a regular basis every year. Leica owners are used to buying lenses which remain viable and useful for generations, not until the next new sensor design arrives, and I'm sure Leica understands that. 

 

Well, the cover glass is part of the optical path and it does influence the images that are produced, so I can't believe they don't consider it when designing their lenses. IMO, that would be foolish.

 

The exit pupil has to be quite long (much longer than is possible with M lenses) for the cover glass to have no influence at all, so I don't think the strategy that your are suggesting for lens design is really a reasonable option. They can design the lenses for no cover glass, as no doubt the lenses designed for film were designed, but then the lenses won't perform as well as if they were designed for a cover glass of a given thickness. I'm not saying that Leica is designing lenses specifically for the thickness of the SL cover glass, but I am saying they are designing lenses for a coverglass that is within the range that they expect cameras to be designed going forward, and without hurting performance too much on at least the M240. This is totally possible. Let's say the cover glass on the M240 is about 1mm and the cover glass on the SL is about 1.2mm (I don't know if these numbers are right, but they likely aren't too far off). They could design new lenses or even reformulated old lenses for an optical thickness of about 1.1mm. This could work well on both cameras. So, I am not saying they are designing for the SL or even the new M explicitly, but I am sure they are considering what they know about the cover glass on the SL and especially the new M when they are designing new lenses and when they are reformulating old lenses. I can't believe they don't model the some sort of cover glass when they are designing the lenses.

Edited by Steve Spencer
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The key, Steve, is that they design the cover glass for the sensor taking into account the lenses that people have, not the other way around. Because even Leica knows that only a tiny portion of their users can afford to (or even want to) change out all their favorite existing lenses for new ones. When they design new lenses, they work on being as compatible as possible with sensors' needs given the constraints of the mount and all the potential bodies that those lenses might be used on. 

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The key, Steve, is that they design the cover glass for the sensor taking into account the lenses that people have, not the other way around. Because even Leica knows that only a tiny portion of their users can afford to (or even want to) change out all their favorite existing lenses for new ones. When they design new lenses, they work on being as compatible as possible with sensors' needs given the constraints of the mount and all the potential bodies that those lenses might be used on. 

 

It sounds like we are much more in agreement, but the trouble is that if the cover glass is too thin major problems develop (and thin cover glass makes the sensor most compatible for lenses designed for film). As we saw with the M8, thin cover glass causes IR contamination. Thin cover glass also more easily cracks--which has been a problem with some people and the M9. Thin cover glass can make a dust shaker to keep the cover glass cleaner harder to implement, etc. So, although Leica has certainly tried to design the cover glass taking account the lenses people have, they have gradually made the cover glass thicker from the M8 to the M9 to the M240, and I am guessing for the next M the cover glass will be a bit thicker yet--like the SL. It now appears that they have tweaked all their currently available wide angle lenses to work better with a bit thicker cover glass, and to me this makes sense. Try to keep the cover glass as thin as possible, but when that doesn't work allow it to be a bit thicker and adjust the lenses that need to be adjusted.

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