High ISO SL2-S, α7III, S1, S5

[Stuart Richardson]

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If your primary use case is M lenses, then the SL2-S is the better choice, as having the offset microlenses on the sensor really do make for better performance. That said, I can say with pretty high confidence that your 75mm 1.4 should perform pretty well on the S5. I have the S1 and SL2, and the 75mm 1.4 is one of the lenses that performs quite well on bodies without offset microlenses, better even than the 75mm APO Summicron. I am not sure why this is the case, but it has been consistent for me across several bodies (S1, A7S, A7Rii etc). The 75mm APO Summicron is indeed sharper on the M cameras and the SL2. The 35mm Summilux v2 is another story...I have the ASPH FLE version and it is another lens that does quite well on adapted bodies. Not perfect or as good as it does on the SL2 or M bodies, but it is not that degraded by comparison. The older summilux lenses are more compact and retrofocal, however, and I think they are more likely to be affected by this issue. They were not that sharp in the edges to begin with, but I expect that on the S1 or S5 they will be very soft even when stopped down to f4 or f5.6. I have a 25mm Zeiss biogon which is similarly retrofocal, and it is only moderately usable in the edges at f11. It is soft at 8 and below and diffraction takes over at f16. If you have the chance, try to shoot both cameras with the lens wide open at a subject a bit further away (focusing too close means that the rear element gets further from the sensor and the problem is minimized), and see if it is ok for you.

[BernardC]

59 minutes ago, Stuart Richardson said:

I have the S1 and SL2, and the 75mm 1.4 is one of the lenses that performs quite well on bodies without offset microlenses, better even than the 75mm APO Summicron. I am not sure why this is the case, but it has been consistent for me across several bodies (S1, A7S, A7Rii etc). The 75mm APO Summicron is indeed sharper on the M cameras and the SL2.

The 75/1.4 is supposedly very similar to the R 80/1.4, so it should perform well on mirrorless bodies, as all SLR designs do. The M 75 APO doesn't have an SLR equivalent (the M 90 APO does, however), so it's probably one of those lenses that sits closer to the sensor. I am over-simplifying, of course. Lots of telecentric lenses have glass that goes almost all the way to the image sensor (especially newer cine designs), but those are always significantly larger than equivalent M lenses.

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[Stuart Richardson]

I have my own suspicions that it has something to do with the floating element as well, but perhaps not. The 50mm 1.4 Summilux ASPH, which is a similar lens design, also suffers from pretty significantly impaired performance on cameras without offset microlenses. Normally you would expect that the longer the lens, the better it fares, but the 35mm Summilux ASPH FLE does better in the edges and corners than the 50mm Summilux does, so I do think it is all a bit more complicated than simply where the rear element lies, as the rear element is aligned with the lens flange in the 50mm, but the 35mm it lies almost a centimeter inside the camera body. I guess it is probably difficult to determine the angle of incidence of the light coming from a complex modern lens design without being an optical engineer. It is easy to envision with symmetrical or semi-symmetrical lenses, but when things get more complicated, I imagine that it is hard to tell from looking at a lens diagram.

Edited January 4, 2021 by Stuart Richardson

[OR120]

2 hours ago, Stuart Richardson said:

If your primary use case is M lenses, then the SL2-S is the better choice, as having the offset microlenses on the sensor really do make for better performance. That said, I can say with pretty high confidence that your 75mm 1.4 should perform pretty well on the S5. I have the S1 and SL2, and the 75mm 1.4 is one of the lenses that performs quite well on bodies without offset microlenses, better even than the 75mm APO Summicron. I am not sure why this is the case, but it has been consistent for me across several bodies (S1, A7S, A7Rii etc). The 75mm APO Summicron is indeed sharper on the M cameras and the SL2. The 35mm Summilux v2 is another story...I have the ASPH FLE version and it is another lens that does quite well on adapted bodies. Not perfect or as good as it does on the SL2 or M bodies, but it is not that degraded by comparison. The older summilux lenses are more compact and retrofocal, however, and I think they are more likely to be affected by this issue. They were not that sharp in the edges to begin with, but I expect that on the S1 or S5 they will be very soft even when stopped down to f4 or f5.6. I have a 25mm Zeiss biogon which is similarly retrofocal, and it is only moderately usable in the edges at f11. It is soft at 8 and below and diffraction takes over at f16. If you have the chance, try to shoot both cameras with the lens wide open at a subject a bit further away (focusing too close means that the rear element gets further from the sensor and the problem is minimized), and see if it is ok for you.

Hello Stuart - thank you for your informative response. I will have a chance (I hope this week) to go into my Leica Store. I will take my 35 v2 and 75 1.4 - and see for myself. I just can't help thinking about the $2,400 difference (S1 vs SL2-S) - but I do drink the Leica Kool-Aid..........