Blue Shift of Bandpass Filters

Here’s a wonderful example of Art based on dichroic filters.

Image "Irdien" by Cris Wood

Art based on “dichroic filters”:  “Irdien” by Chris Wood          with kind permission of the artist

We notice that the colors change at different angles of the filters.

Even more visible here :

Art based on Dichroic filters : Photo used with kind permission of the Artist: Chris Wood,

We notice especially that for filters of the outer circle, filters that  have a 90 degree different orientation have about the same color transmission. Especially look at the topmost, the rightmost (both orange colored) and the top-right-most filter (with a purple touch)

Below is a calculator that gives an idea about the resulting interval of wavelengths (called “band” ) when you use the filter at some angle off the designed incident angle.

The filters above seemed designed for an incident of 45 degrees to the surface. Thus +45 and -45 degrees result in the same color and in between we get a blue shift of the wavelength that pass.

The calculation is just for the primitive case of a rectangular transmission curve.