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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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    \$\begingroup\$ 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? \$\endgroup\$
    – laurencemadill
    Commented Aug 9, 2017 at 15:18
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    \$\begingroup\$ 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? \$\endgroup\$
    – scottbb ♦
    Commented Aug 9, 2017 at 15:23
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    \$\begingroup\$ 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. \$\endgroup\$
    – user50888
    Commented Aug 9, 2017 at 19:02
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    \$\begingroup\$ Why not just replace the strings with nylon or gut for the shoot? \$\endgroup\$
    – Carl Witthoft
    Commented Aug 10, 2017 at 11:26
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    \$\begingroup\$ @CarlWitthoft nylon or gut strings on an electric guitar? First, the largest 3 strings in a nylon set are wire wound, just like steel strings, so that doesn't fix the problem. Second, nylon strings on an electric would look weirder than the orange/blue artifacts. Like, uncanny-valley weird. \$\endgroup\$
    – scottbb ♦
    Commented Aug 11, 2017 at 8:01

2 Answers 2

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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!

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  • \$\begingroup\$ This will happen with "flatwound" strings and those that are not single strand (monofilament-like) drawn strings without fine lines. \$\endgroup\$
    – Stan
    Commented Aug 13, 2017 at 21:38
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To anyone reading this in the distant future 2021 and beoynd.

You can also remove the aliasing by capturing red, green and blue separately.

Assuming you are using a tripod, you can shoot with color filters or gels in front of the camera. (Or gels in front of strobes, but that requires a pretty dark room.)

Take one shot per red, green and blue color. Either shoot in black and white on the camera, or convert each shot to black and white in post.

Then, merge the three layers, with each layer representing red, green and blue. This can be done in Photoshop or with tools such as ImageMagick.

This will remove any aliasing, but requires that the setup is stable enough to not move the camera or subject between exposures.

The idea is not a new one.

enter image description here

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