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Sony FE 50mm f/1.2 GM Aperture Series: Example of Unacceptable Lens Skew

The Sony FE 50mm f/1.2 GM is a high performance optical design. My guess is that it is difficult to manufacture without significant sample variation, since the high performance makes high precision assembly essential. So some variation must be accepted. And quality control including too-strict standards can be prohibitively expensive. But when quality control allows obviously troubled lenses to leave the factory it means either that standards are far too loose, or something is awry with the QC process.

A dozen years of doing what I do tells me that sample variation issues exists with just about every manufacturer. It is NOT specific to Sony. You just have to be on the lookout for bad samples. Basically, you are the QC department and need to reject samples that show obvious faults.

The first two samples* I tried showed slight asymmetry but well within what I would consider typical, and really quite good for an f/1.2 lens. And well within the lens mount / sensor parallelism tolerances. See Sunrise Over Patriarch Grove.

I got around to buying my own sample, and it is shockingly cockeyed (lens skew). It will be going back. This page shows one image, but I shot it after seeing obvious skew near and far in other images.

Sony FE 50mm f/1.2 GM Lens Skew

The wooden steps are themselves somewhat warped, but I shot my known-good Voigtlander FE 50mm f/2 APO-Lanthar as a control (my 50mm reference lens); it shows near-perfect symmetry and sharpness across the steps. That rules out the camera and/or subject alignment, proving that the lens is the culprit. It also satisfies me that the brand-new Sony A1 is not at fault.

Lens Skew on wooden steps
f2 @ 1/2500 sec, ISO 100; 2021-07-08 15:33:49
Sony A1 + Sony FE 50mm f/1.2 GM RAW: LACA corrected, vignetting corrected

[low-res image for bot]
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