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Leica 50mm f/2 APO-Summicron-SL ASPH Aperture Series: Unacceptable Optical Swing (Lens Skew) + Reader Comments

UPDATE: I added another example of the lens skew (optical swing), showing that even F/5.6 cannot hide the problem. What a turd of a sample. How in hell did it leave the factory?

The Leica 50mm f/2 APO-Summicron-SL ASPH is an ultra high performance optical design, as per its claimed MTF performance. IMO, a better approach would be to publish a guaranteed minimum MTF performance based on testing real lenses.

High performance lens designs are difficult to manufacture to specifications, but according to the video with Peter Karbe of Leica, the optical design is such that small spacing errors of lens groups should have little effect on performance, and the lens groups are matched in order to work synergistically. Similarly, the claim is made that assembled lenses have real MTF very close to the computed-best MTF.

But the brand-new Leica 50/2 APO that I am shooting repudiates the assumptions that one might take away from that video. Moreover, if it met Leica quality control standards at the factory, then I say that Leica quality control standards need improvement. My comments of course are on this one sample—I have no idea how much sample variation there is among Leica SL lenses. The 28/2 APO-SL and 35/2 APO-SL were both superb.

Everything I am shooting at distance shows a visibly-soft left side of the frame (when focused at center or to the right). With no way to try another sample while on my trip, this is really frustrating.

Leica 50mm f/2 APO-Summicron-SL ASPH: Lens Skew, Optical Swing

The Leica 28mm f/2 APO-Summicron-SL ASPH has excellent symmetry—no complaints, it is a beautiful performer consistent with its claimed MTF. And yet, wider-angle lenses typically have more symmetry issues. I just love the 28/2 APO, so I’d really love to have a 50/2 APO with similarly good behavior.

Southern spur of Mt Conness
f2 @ 1/1600 sec electronic shutter, ISO 100; 2021-09-20 12:25:26
LEICA SL2 + Leica 50mm f/2 APO-Summicron-SL ASPH
ENV: Mt Conness area, altitude 10100 ft / 3078 m, 65°F / 18°C
RAW: pull 0.66 stops, +10 Whites, +10 Clarity

[low-res image for bot]

Reader Fred Miranda of writes:

I saw your note on the 50/2 APO-SL optical skew. It’s a very large swing IMO. Although better than other brands, I find that Leica is not flawless.

From my recent experience, the followed lenses were noticeably tilted, swung or both:

• One Leica 50mm f/1.4 Summilux-SL
• Two Leica 50mm f/1.4 Summilux-M ASPH
• One Leica 35m f/1.4 Summilux-M ASPH FLE
• One Leica 90mm f/2.8 Elmarit-M (this was the oldest one but still 6-bit coded and latest manufacture date) [diglloyd: maybe a typo on that lens name]

Quite surprised since most of them were demo copies with no signs of usage (abuse). I was able to correct the SL 50/1.4 Lux since is was just a simple tilt. (using shims) but decided to return the other ones for better copies.

DIGLLOYD: from what I can tell, every manufacturer has quality control problems. It must be a hard problem to solve; maybe it can be detected but not easily fixed? But if an end-user can shim a lens, surely the manufacturer could do so at the factory, and design lenses to make it easy to do so.

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