Some great advice provided by Greg and Peter.
An alternative for you Greg -
http://www.sciencecenter.net/hutech/...lter/index.htm
I've used Astrodon and Custom Scientific filters. Astrodon are perhaps a little easier to process as Greg indicates, but you're kidding yourself if you think your colour balance ratios are as advertised (1:1:1). I've found subtle differences post G2V calibration (subtle in that they range from +/- .4). This was averaged over 5 calibration runs. I now use the Custom Scientific set. Really like the rich saturation they deliver, especially the red filter where there is no cross-over - great for RRGB images where R is also used as the luminance. I work on the assumption nothing is parfocal, thus all ways refocus between filter changes- ~70sec for the FocusMax routine including AcquireStar platesolves. So not too much of a time waster.