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Leica 90mm f/2 APO-Summicron-SL: Stopping Down Gets Worse at f/2.8 and f/4.

So yesterday I shot the Leica 90mm f/2 APO-Summicron-SL rigorously, and by chance got the most beautiful lighting I had seen in years.

What does the Leica 90mm f/2 APO-Summicron-SL do? Degrade excellence at f/2 into softness at f/2.8, more softness at f/4, recover (almost) at f/5.6 to f/2 quality. Looks like a very bad focus shift, but I now have to go prove that out, to rule out other oddball potential causes (operator error is NOT one, as I have already confirmed).

But one thing is clear: the size (magnification) of the image shrinks slightly with each stop, which means focus is shifting rearward (towards the distance). In past testing this has always meant optical focus shift, with the exception of the electronic focus-changing glitches with the Fujifilm GFX-50S and the Fujifilm GF 120mm f/4—and in that case there was no consistent pattern. A consistent pattern as with the Leica 90/2 SL has always meant strong focus shift.

It’s not a single series thing, but repeatable, though not always obvious or clear—could it have something to do with Multi-Shot High-Res mode, where the losses are plain to see? Either it’s a major focus shift or some weird mechanical or electronic glitch. I am furious that my work is toast, in terms of showing what the lens can do. If it’s optical, then I deem the lens useless. If not... I don’t yet know.

The Leica 90/2 SL can deliver truly outstanding images, but this behavior has me frustrated beyond printable words. And maybe the portrait focusing errors can be explained in part too, if it is indeed optical focus shift—that would surely screw the pooch for portraiture, as was the case.

I now have to research the problem and figure it out. I assume its 75mm sibling will behavesimilarly.

Given the atrocious field curvature and focus shift of the “reference lens”* Leica 50mm f/1.4 Summilux-SL ASPH, maybe it’s just normal (see Sharpness Losses from Field Curvature at Distance: Grassy Meadow and other series).

Could the Leica SL build in some kind of compensation for severe focus shift that the Panasonic S1R does not? If so, it must be new because it did not when I last tested the Leica SL. Compensation is NOT a solution for many shooting scenarios: how does one focus in dim conditions except at full aperture? That’s one of my most common use cases!

* “Reference lens” is Leica-speak for “a lens demonstrating pronounced field curvature and focus shift that would make any other manufacturer would blush”.

James K writes:

You are in photo hell. One way of providing some insight into the mystery would be to shoot the Leica 50mm f/1.4 on the Leica SL and see if it behaves the same as on the Panasonic. If it does not exhibit the extreme focus shift on the SL you will have determined that there is a software issue. The idea of the common L mount might not be working with lenses using compensation programs to address optical flaws.

DIGLOYD: Leica gear has been the most problematic of all camera systems over the years.

I don’t intend to borrow the Leica SL as it’s pointless at this juncture—I’m not into 24 megapixels and crappy ergonomics/haptics, so it’s a non-starter camera as far as I’m concerned. I’ll have to run some more tests and I now also have the Leica 75mm f/2 APO-Summicron-SL ASPH along with the 90/2.

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