Quote:
Originally Posted by PRejto
The Astronomik is 1mm thick. If you replace just the blue you will lose parfocality (if there is such a word!). Also perhaps the way blue/green filters overlap or don't overlap may change the way cyan is reproduced. Who knows what you'd get mixing two brands of filters?
Peter
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My blue is not quite parfocal anyway, the filter is but it rarely is truly parfocal in most refractors. Just means I'd have to refocus which I do anyway.
The difference between the blue cutoff on the redder end appear to possibly be about 5nm (520v515) by eyeballing the graphs. The major difference in the blue appear to be the UV cutoff.
Both greens appear to have the same lower end but the Astrodons are narrower (end cut of 565? vs 580 of the Astronomik). The reds start at ~595 (Astronomik) against the 615 (Astrodon).
Changing the blue filter just cuts more of the UV. The biggest changes come from the green and red where Astrodon has a much larger gap (light pollution).