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Originally Posted by johnnyt123
Dave
I can't say how much I appreciate your feedback.
Hopefully in time my skills with astro imaging will resemble yours.
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No worries, John. I'm only a few months ahead of you... having bought my first CCD only 10 months ago
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First thing I am going to do is purchase a moonlite focuser for my Megrez to automate the focusing process when changing between filters.
I assumed when Astronomic and Astrodon say their filters are par focal then one would assume they are truly par focal. But this is not the case. One mistake I made was focusing using the luminance filter then assuming the RGB filters are at the same focal length.
Assuming the filters are perfectly flat and the surfaces are parallel I don't understand how the light is being refracted changing the focal length. So I also assumed the all the filters would be parfocal.
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When I say "not parfocal", I'm talking really really tiny amounts. Without a motorised focuser and software-assisted measurement of star sizes - I highly doubt you'd be able to tell the difference. Notice how your out of focus stars all look equally out of focus in R, G, and B?
It looks to me very much like you accidentally focused with your Astrodon Ha filter instead of Astronomik L. I get similar results if I focus with my Astrodon Ha and then try to shoot images with my Baader LRGB filters.