What Causes the Colorful Cross in Photos of Sirius?

[pixel01]

My friend took this picture of Sirius. He put 2 strings as a cross in front of the lens and there is the cross in the pic. But we do not know why there's the color of the cross, it resembles the color of a rainbow.

 

[Dadface]

What a wonderful effect.To me it bears a closer resemblance to white light interference fringes.Perhaps subsidiary images are produced by diffraction at the four corners where the two strings cross and the light from these then interferes.This is only a guess and I would like to hear what other people think.

 

[russ_watters]

Yes, I think they are interference fringes. They get even wackier when you use unusual filters like a hydrogen alpha filter and then map it as regular red (lens flares, too): http://www.russsscope.net/images/Horsehead-HaRGB.jpg

 

[flatmaster]

This may be a silly question, but would the cross of light line up with the cross of the strings, or would it be rotated by 45 degrees if interference is the cause?