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We're doing a photoshoot of a guitar collection. The photos are coming out great, but there is a specific color aberration on the strings. The guitar strings are braided by a thin metal wire, which probably causes reflections and interference of the reflected light. (Please see the picture)

enter image description here

We've tried to get rid of the color errors but without any luck. Now we are quite desperate so any help would be greatly appreciated.

We're shooting on a Hasselblad H3Dii with a Hasselblad 80mm lens.

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    It would be useful to know what lighting setup you're using, or if you're using natural light. It's possible that this is just caused by reflected light, but there could be more to it than that. Have you tried adjusting the orientation of the camera slightly to see if it still does the same? – laurencemadill Aug 9 '17 at 15:18
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    I was just going to suggest what @laurencemadill suggested. Try rotating the camera 45°. Does that change the "frequency" of the color shift pattern? Also, try changing the distance between the camera and the guitar. Does that change the frequency of the pattern, or the color shift of it? – scottbb Aug 9 '17 at 15:23
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    Zooming in, there are orange and blue artifacts in many locations. There is a large one between the two drawn arrows on the body. There are smaller artifacts on the adjacent string and orange and blue artifacts on the frets under the smaller strings to the left. There is a blue patch on the pickguard screw. I suspect that size of the particular artifacts in question are due to the lack of an anti-alias filter at the camera sensor...speculation but this is common in digital medium format. The windings on the string may be below the Nyquist limit. – user50888 Aug 9 '17 at 19:02
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    Why not just replace the strings with nylon or gut for the shoot? – Carl Witthoft Aug 10 '17 at 11:26
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    The only thing that can be done to deal with a signal sampled at less than the Nyquist frequency is to low-pass filter the input signal to satisfy the Nyquist frequency. That's exactly what an antialiasing filter in a camera does. Other than that, you have to perform signal processing to do your best to make the signal look right. But once aliasing has been recorded, the damage is done. The best you can do after that is just triage. – scottbb Aug 11 '17 at 9:44
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We've just figured it out. As Ben Rudgers correctly pointed out, the problem is caused by the lack of anti-aliasing filter on the Hasselblad sensor. It produces much sharper pictures, but with a lot more moiré.

Knowing this, we've just used the moiré reduction feature in Lightroom. The feature is quite "hidden", but once we found it, it solved the issue completely for us.

You can read about the moiré correction feature here:

https://scottkelby.com/a-little-known-feature-of-photoshop-and-lightroom-to-the-rescue/

Thanks everyone for your comments!

  • This will happen with "flatwound" strings and those that are not single strand (monofilament-like) drawn strings without fine lines. – Stan Aug 13 '17 at 21:38

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