"Jan van Gastel" wrote in message ...

I don't think I agree with your statement, that optical quality is less
important for observing DSO's then it is for observing planets.

Well, high optical quality is *always* beneficial, if you can afford it.
There's also many different kinds of optical quality. Ideally, a
reflector should have a mirror with a highly accurate figure, smooth,
and well baffled against ambient light. For viewing planets, a good
figure is essential and a smooth surface is fairly important, but
baffling is quite irrelevant, because the planet will easily outshine
any other light. For viewing galaxies, baffling is very important,
a smooth surface is fairly important, and a good figure is relatively
unimportant, because most visible detail in galaxies is very large
compared to the size of the Airy disk.

But there are always exceptions, which is why it is always nice to
have an optical system that is good in every way. Even galaxies can
have bright cores that show fine detail. And M42 challenges a
telescope in every possible way. The Huyghenian section is bright
enough to show sub-arcsecond detail where the figure is paramount.
Observing the E and F stars requires both a good figure and a
smooth surface. And the outer reaches of M42 are as faint as any
the outer arms of a galaxy, requiring a smooth figure and good
baffling. Likewise with planetary nebulae; it is very common to
have both a bright section that takes the highest possible
magnification and a very faint section that challenges your
faint-fuzzy skills.

- Tony Flanders