Saturday, April 7, 2012

Parfocal test of Baader narrowband filters


There aren't many nebulae in my sky right now, and the full moon means there's no point in traveling to a dark sky site to work on my M101 project. So tonight I'm going to investigate how parfocal my Baader Ha/SII/OIII and LRGB filter sets are. I don't expect the two sets to be parfocal with each other.

It's a simple plan at this point. I'll use 20 second exposures of bright stars taken through a Bahtinov filter. The stars are chosen to span the spectral range from blue to red: Altinak (spectral type O), Sirius (A) and Betelgeuse (M). Best focus of Ha will be the starting point, and then I'll cycle through the other filters and shoot another Ha to catch any focus drift.

Once the narrowbands have been tested, I'll repeat shorter exposures with the LRGB, initially focusing the L filter.

After that I may move on to shooting more long-exposure images in Ha of M101.

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