I thought that the minimum requirement is precise straight lines to make clear diffraction spikes and that it may be possible easily with fine fishing line.
You can see two sets of diffraction maker. The left is for my refractor. This is made of fine fishing line and a round toy badminton racket for kids. You see a sample here: http://www.johnlewis.com/230417814/Product.aspx
The right is for camera lenses. This is made of the same fishing line, alpha-cyanoacrylate adhesives, and a cheap round towel ring.
Setting was easy and cheap with Scotch tape.
This is a 100% crop showing the spike with the racket and my refractor at F3.6. The lines are a little bold. I suspect it due to the fact that the racket is not exactly round.
Thanks Dennis Sakve, I could be confident about focussing for the first time.
-------------------- hiro
Canon EOS 5D-AP by IDAS / EOS 5Dmk2 sp2 by Seo san
Takahashi FSQ-106ED with reducer, extender, and "hiro design" off axis guider
Lenses by Canon, Nikon, Leica, and Zeiss (Cosina)
Takahashi EM-200 temma 2 jr / Kenko Skymemo-R
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