I've been using the Bahtinov masks for a while now. Amazingly easy to focus. I just finished a 24" mask for an OGS RC that our club has. I'm holding a 10" mask next to it for comparison.
-------------------- Tak FSQ-106EDX
Pentax 75 EDHF 75mm f/6.7 APO
Apogee Alta U8300 CCD
Orion Atlas EQ-G Mount with EQMOD