GR and BG filters? Do such things exist?

[vlaiv]

Not sure if title is descriptive enough (-R and -B might be better naming?), but I wondered if there are filters that are like regular R, G & B filters but instead of passing one band, they block one of the R, G or B bands?

I have sneaky suspicion that using L + 2 of those filters would yield better results in terms of SNR per imaging time than standard LRGB combination. Rational behind this would be:

1. wider filter lets in more signal per unit time - hence boost in SNR

2. If we look at the frequency response of LRGB filters we will notice that with a little math, R, G and B can be reconstructed from L, GR, and BG filters like this:

G = BG + GR - L

R = L - BG

B = L - GR

added benefit will be of increased SNR of each component, because when we add channels we are effectively stacking read and dark noise, thus lowering those. We lower shot noise as well but it is not straight forward as with read and dark noise - it depends on target frequency response and distribution of light in filter bands.

[Alien 13]

Would not Cyan Magenta and Yellow filters be the same thing and I believe they do exist and have been used for AP. http://www.astrosurf.com/buil/us/cmy/cmy.htm

Alan

[vlaiv]

 

59 minutes ago, Alien 13 said:

Would not Cyan Magenta and Yellow filters be the same thing and I believe they do exist and have been used for AP. http://www.astrosurf.com/buil/us/cmy/cmy.htm

Alan

Indeed! I did know about Cyan, Magenta and Yellow, but it did not occur to me to check their frequency curves!

Thanks!

[Stub Mandrel]

Alan got there before me!