[jase (Jason)]

The gap between the green and red wavelengths is intentional and is a characteristic of the SBIG/CS RGB filters. If you read the .pdf document I provided (http://www.sbig.com/pdffiles/SBIGFilterSet.pdf) it explains this well.

“There is a “hole” in the new filter set between 570 and 610 nM. While this may offend the purist, there are no significant astronomical emission lines in this hole. Stars have very wide spectral distributions, so no loss of information results from this hole – you do not miss “yellow” stars (which are yellowwhite). However, sodium vapor streetlights terribly pollute this region, …” page 5 of above document.

“There is a “gap” between the red and green filters -The gap in intentional. It reduces the effect of light pollution and misses no important emission lines. The gap was necessary to balance the counts from a sunlike star.” Page 6 of above document.

The SBIG/CS LRGB filter set purposely minimises colour cross over, which provides excellent contrast with clean emission lines. I’d like to note that this gap is only present on the RGB set - the CS UVBRI filters include this emission line for photometry data collection.

I'm happy to also elaborate on colour cross over techniques used by Astrodon, but will leave this for another day.