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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.

Example

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.

  • Make better images by learning how to get the best results right away. For example, the best way to set up your Sony camera.
  • Save money by choosing the right lens for your needs the first time, particularly with the numerous lenses available for Sony.
  • Make better images, a sort of “cheat sheet” saving yourself months or years of ad-hoc learning—best practices and how-to and processing parameters are discussed and shown.
  • Jaw-dropping image quality found nowhere else utilizing Retina-grade images up to 28 megapixels filling up to 5K display, plus large crops.
  • Real world examples with insights found nowhere else. Make sharper images just by understanding lens behavior you won’t read about elsewhere.
  • Aperture series from wide open through stopped down, showing the full range of lens performance and bokeh.
  • Optical quality analysis of field curvature, focus shift, sharpness, flare, distortion, and performance in the field.

Want a preview? Click on any page below to see an excerpt as well as extensive blog coverage, for example on Sony.

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

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