Interesting comments jase, I can understand your points.
It definitely feels like I get less image data when using the Astronomik Luminance filter than without, but I have to admit I haven't done any scientific testing of it - I will do that and see what the results are, I'll be most interested.
Focussing is an issue for me, it's very rare that I can perform an auto-focus on the FOV that I'm imaging. There's never anything bright enough (small FOV, faint galaxies, purposefully removing bright stars that might bloom, avoiding it trying to autofocus on a galaxy, etc). So refocusing for each filter isn't practical.
You mention determining an offset for focusing - not sure how I would integrate that with my imaging runs in CCDSoft or CCDCommander.
Considering those focusing issues the "sure it makes imaging a little easier" means it's more like "it makes imaging a lot easier" for me
Roger.