I made a Hartmenn mask with two holes out of construction paper for my
8" SCT. It helped a lot but I know the holes are not perfectly round and
not exactly centered on the corrector. So, Your suggestion of a strip of
foil sounds interesting.. I to want to hear more! Width, Length,
Placement,...

--
Michael A. Barlow
"Thomas M" wrote in message
news:d0o1c.55946$A12.10299@edtnps84...

One alternative that also works well for star focussing, is a simple
piece
of aluminium 'strip'. This can be a lot lighter than the mask, and
simply
hangs on the dew shield. It produces a single pair of diffraction
spikes.
If
there are two spikes each side, you are not in focus, and as you focus,
the
spikes move together, become one, and then move apart again as you go
through the focus point.

You mean just hang a strip of foil? How wide should it be? How is it
hung?
If the scope is tilted, the strip will not just hang free. What do you
mean
exactly?

Thanks