Bahtinov mask

Not sure whether this is the best forum area to post about this but I have not been able to find anywhere better.

Focusing my scope has always been a royal PITA. For a start the focuser is a relative, not absolute, positioning device with significant backlash.  That could presumably be fixed (or, at least, altered) with some investment in new hardware.  FocusMax has real problems doing anything useful. It generally throws a tantrum and proceeds to rack the mechanism in or out as far as it can.

Driving things by hand has been the way until tonight.  Attempting to minimize a stellar FWHM is fine as far as it goes but the ever present variable seeing makes it harder than is desired. How do you distinguish between an out-of-focus star during a period of good seeing and an in-focus counterpart during bad seeing?

Yesterday I downloaded a SVG file for a Bahtinov mask suitable for the 0.4m Dilworth. Persuading a printer to chop it into A4-sized chunks and reproducing it at full scale was another PITA.  However, it worked eventually and the bits of paper were glued onto a sheet of cardboard  which was then attacked with a craft knife.

Outstanding success!  I can heartily recommend a Bahtinov mask.

Never thought I would rule a diffraction grating with a Stanley knife though …