What the subject line said.

I already had an SM40 from, oh geez, probably almost
a decade ago, so from what I'd heard, it made sense to
buy a PST to double-stack the SM40 on it.

Oh yes.

The detail is really quite something--just about the best
I imagine you could get from a 40 mm scope. With
just the PST, there's a lot of scatter in the image, which
reduced contrast; with just the SM40 on my Ranger, the
details were there, but not as distinct. The two of them
put together made the Sun fierce and unsubtle. A few
caveats: The PST comes with the 5 mm blocking filter;
I bought my SM40 with a 10 mm blocking filter, so the
PST had a bit more vignetting than I was accustomed
to. There is no way (as far as I can tell, at least) that
one can replace the blocking filter in the PST. The PST
comes with a helical tuning ring; the SM40 comes with
a small tuning knob. These are adjusted together to
tilt the two filters so as to obtain the best image. I think
they tilt along the same axis, because there's a kind of
linear vignetting that (in my case) goes diagonally across
the field of view.

Still, for only an extra $500 or so (I bought the PST at
PATS in Pasadena, and got the case thrown in as a
freebie), it's a fantastic deal.

--
Brian Tung (posting from Google Groups)
The Astronomy Corner at http://www.astronomycorner.net/
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