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I used mine on the 200 600 and A7R4 a few times, and never thought it affected IQ badly at all in good light, which is something you need given the smaller max aperture. When the light was poor there was a small drop, but not unusable. Maybe it's too short a period to have tested it? There are many factors that can affect things, I'm sure you know. I sold mine, but just because I wasn't using it and it helped fund other lenses.