(Dave Mitsky) wrote in message . com...

I'd like to hear your opinions on whether a 127mm Orion
Maksutov-Cassegrain is a better deep-sky telescope than a 10" Orion or
Hardin Dob that is now on sale for about the same price. Don't laugh I
have a very good reason for collecting this information.

Gosh, how good can your reason be ...

Seems simple enough to me. For deep-sky observing, a bigger scope
always shows more than a smaller one, with three exceptions:

1. The bigger scope has very poor optics (inherent or due to
poor collimation, thermal problems, etc.)
2. The object being examined doesn't fit in the FOV of the
larger scope but does in the smaller scope.
3. The object in question has extremely low contrast, and the
bigger scope does significantly worse in this arena.

I've viewed through a couple of Orion 10" Dobs, which had perfectly
fine optical quality, and I've had extremely reliable sources vouch
for the quality of the Hardin 10". So #1 is out.

Because of its very low f/ratio and its 1.25-inch focuser, the Orion
Mak-Cas actually has a *smaller* maximum FOV than most 10-inch Dobs.
So much for #2.

Case #3 is quite rare, and decent Dobs have pretty good contrast,
and the contrast of the Mak-Cas is inevitably limited by its CO.
So there can't be many cases, if any, where the Mak-Cas wins in
this department.

That means that the only way the Mak-Cas can conceivably be called
a better deep-sky scope is if you end up using it more because of
its portability. That, obviously, is going to depend on the user
and the details of his/her situation.

- Tony Flanders