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EXCERPT page containing first few paragraphs. 2021-10-22 12:38:09

Lens Diaphragm / Aperture Symmetry

Kaz T writes:

I was wondering if the aperture on your RX1 closes symmetrically. Mine doesn't. Granted, it's subtle, but it does affect the shape of pinpoint OOF discs. I returned it and got a new one, but it has exactly the same problem (same blade sticking out just the same amount). I'm not the only one, as there are posts on sony's site as well as dpreview, and photos show exactly the same problem.

This is surely disappointing, but also normal and also not new: some Zeiss lenses for DSLRs show the same behavior. This is not to say it is desirable, but it does occur and is considered normal.


A small gray circle is inscribed as reference. Observe that the diaphragm is not quite circular—nicely rounded, but also slightly mishapen. This behavior is not a defect according to Zeiss. But it cannot be called desirable. Still, field shots do not suggest any negative effects.

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Diglloyd Guide to Mirrorless offers comprehensive integrated coverage of most APS-C and full frame mirrorless cameras and lenses.

Special emphasis is placed on Sony full-frame, including Sony lenses and the high performance Zeiss Batis and Zeiss Loxia lenses plus Rokinon/Samyang and others. Fujifilm X, Olympus and Panasonic M4/3, Sigma dp Merrill and dp/sd Quattro are also covered in depth. Years in the making, it offers a wealth of material for choosing and using a mirrorless camera.

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  • Optical quality analysis of field curvature, focus shift, sharpness, flare, distortion, and performance in the field.

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Sony RX1 with its Carl Zeiss 35mm f/2 Sonnar T at f/4

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