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I shot these images with my Sigma 24–70 and Sony A7iii, in fog, sometimes pointed into the "sun" (it was not actually sunny but sometimes the lens was pointed towards the direction of the sun). I believe they were shot at above 1/1000th of second. I have front e-shutter disabled.

I've only ever seen this happen with Sigma lenses (24–70 and 85) on my A7iii, not other brands. I'm not saying it's not possible, just that I've never noticed it. It seems to happen regardless of the lens hood being attached or not.

I'm wondering why there is a darker shadow on the left side of the frame with a semi-circle/halo-like pattern there.

sigma lens aberration example

sigma lens aberration example

sigma lens aberration example

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  • \$\begingroup\$ Do you have a filter on the lens? A lens hood? Some other sort of attachment? If you detach the lens and look through it, is the "shadow" there? Have you inspected the sensor? \$\endgroup\$
    – twalberg
    Jul 3, 2021 at 19:06
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    \$\begingroup\$ Do you have Lens Compensation activated? Have you try to deactivate it? \$\endgroup\$
    – Romeo Ninov
    Jul 3, 2021 at 20:18
  • \$\begingroup\$ @RomeoNinov I had Shading: Auto, Chromatic Aberration: Off, Distortion: On \$\endgroup\$
    – jonathanbell
    Jul 4, 2021 at 15:54
  • \$\begingroup\$ @twalberg No filter or hood on. However it happens when the hood is attached also. I'll take a look at the sensor and lens today. \$\endgroup\$
    – jonathanbell
    Jul 4, 2021 at 15:54
  • \$\begingroup\$ @jonathanbell, just try to switch all of them off \$\endgroup\$
    – Romeo Ninov
    Jul 4, 2021 at 16:03

2 Answers 2

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Sorry for the bad news:

Semi circular artifacts especially on a fast shutter speed are usually an early indication of shutter failure on the a7 III.

Examples:

Semi Circular Artifacts due to shutter failure

More Circular Artifacts

Please inspect the edges of your shutter curtains for damage. The shutter edges should not be rough in any way. Often on the a7 III the shutters starts serrating which is reported as more sensor dust. Then the chance increases that these serrations start to catch on some other part of the shutter which will then destroy the shutter for good.

Example of serrated shutter curtain: Metal shaving from shutter box of A7iii?

Cost for replacing the shutter is approximately $300. If the camera is still under warranty, you better act quickly.

See also here for similar effects, which have been reported back as shutter damage. https://www.dpreview.com/forums/thread/4286654

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  • \$\begingroup\$ Apologies for the late reply (I was away) and thank you for this information. Sadly, yes, I do notice a slightly rough edge along the shutter at the "bottom" with the lens off (it looks a lot like your example from the link in your answer). Darn! I guess I will be looking into replacing the shutter. What about shooting with just electronic shutter or "e-front curtain" for now? Thoughts? \$\endgroup\$
    – jonathanbell
    Jul 14, 2021 at 23:11
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    \$\begingroup\$ Full e-shutter will not exhibit the problem and can be used as a possible solution. I am not sure about the e-front curtain. As the thw curtains then don't pass each other, it might work as well. \$\endgroup\$
    – Kai Mattern
    Jul 16, 2021 at 3:48
  • \$\begingroup\$ Thank you again! This was very helpful. \$\endgroup\$
    – jonathanbell
    Jul 16, 2021 at 10:59
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I had this problem, it might be the shutter, but when I set the E-front curtain shutter to "On" the problem disappeared.

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    \$\begingroup\$ Unfortunately, this will only delay the inevitable shutter failure. However, a good workaround for the moment. \$\endgroup\$
    – Kai Mattern
    Sep 5 at 8:29
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    \$\begingroup\$ Yes. OP here with a follow-up. The well known issue with the A7 II shutter was exactly my issue here. E-front shutter works as a workaround but only e-shutter (or shutter replacement) will actually get rid of the issues. Sorry for the bad news. \$\endgroup\$
    – jonathanbell
    Sep 5 at 17:26

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