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I run into a little issue today and can’t figure out the root cause.

I have the a6400, when I get close to a subject, mostly black / dark fabric type of material, I will see a red dot (light / flare) on the subject, as I move further, it turns into a circle, and it stays on the final shot.

It happens with both the 35-50 kit lens and the sigma 16mm,

It’s also not Focus Illuminate, I tested with it turned off and issue persisted.

And it DOES show up on the final image, sadly...

Any idea what this could be?

Big thanks for looking into this!

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Click for larger.

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    Welcome to SE. You might add whether your problem appears in the final image taken by your camera or if it is only visible in the EVF. – Gerhardh Jul 11 at 7:54
  • Thank you! And sorry I should have added that! It does show up on the final image! – iWillLift Jul 12 at 0:38
  • Then it would probably be useful to add an image that contains the effect instead of a photo of the camera display. – Gerhardh Jul 12 at 0:45
  • The final image just looks exactly like what it shows on the display though, if that makes sense? Like it doesn’t change colour or shapes it just looks exactly the same as it shows on the camera display – iWillLift Jul 12 at 4:14
  • Just uploaded a final image that shows the red flare – iWillLift Jul 12 at 6:00
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What you're seeing is colour moiré. Basically, you're paying the price of having a lens and sensor that can resolve the tiny detail of the weave of the fabric, but not quite the resolution needed to determine the colour because we use a Bayer-pattern colour filter to determine the colour.

Note that the effect is only happening at a limited range of distances from the camera for a given fabric and zoom setting. What that tells you is that the camera can't quite cope with threads that are in a certain range of sizes on the sensor. Any closer, and they're big enough for the "figure out what colour it is" calculations have enough data to work with. Any further away and the threads are too small to be resolved clearly. Get the distance just right, though, and the pattern of threads line up in weird ways with the pattern of green-, red- and blue-filtered pixels. Instead of seeing a more-or-less neutral colour with lighter and darker areas (the shadows and highlights on and between the threads), it sees little areas where the red is missing or very bright, or the blue. (There are twice as many green pixels, so green is rarely a problem.)

The easiest way to fix moiré is to change either your shooting distance or your zoom setting. There are various ways to attack it in post-processing with varying degrees of success, but none of them are perfect. (You can also use a multi-shot camera or one with a full-colour sensor like the Foveon to eliminate colour moiré, which just leaves luminance moiré with even smaller details.) Changing your distance may mean cropping to get "the same picture", but it's better than weird colours that weren't there, or trying to fix weird colours that weren't there, especially if you care about the details.

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  • THANK YOU SO SO SO SO SO SO MUCH for the incredible detailed answer!!! It makes TOTAL SENSE! Since the most still product shots are all mostly fabrics, athletic clothings specifically, and I place them on my bedsheets, hence why I could only reproducing the issue easily but as soon as I change a scene, it’s gone. And that also explains why it changes from red dot to circle based on distance and then it’s gone when I moved away. I did a bit more research on Moiré now so learned a lot, guess Ima have to invest in a 30 or 50 mm instead of using my 16mm. Thanks so much!!! – iWillLift Jul 13 at 6:42

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