"Tom E." wrote in message
...
"Tony Flanders" wrote in message

If cooldown time is an issue, a 4" refractor would probably make
sense, and if not, a 6" - 8" catadioptric or Newt would be better
yet. You can also get a Newt to cool down reasonably well in you're
willing to install a fan.

- Tony Flanders

I already have a 114mm newt, a cheapo, and don't really want another one.
The supplied eyepieces were a 20mm, which at 900 f.l. only shows a small
white disk for Jupiter, and the supplied 4mm couldn't resolve.

The 114 "cheapo" is a poor example of what a Newtonian can do. Also, focal
length really is not the limiting factor for achieving high
magnification/high resolution, it is only one of two factors in achieving
the desired image scale (50x, 100x, ... 200x).

Resolution is an aperture thing in combination with a telescope objective's
ability to maintain a high contrast transfer of energy through the system.
IOW, it takes bigger aperture with higher contrast (better quality of figure
and smoothness) to improve the views, not more focal length.

For this discussion, focal length is just a factor in choosing your
eyepiece. A 1000mm focal length, 4" aperture telescope, with a 10mm eyepiece
provides 100x. But so does a 500mm focal length, 4" aperture telescope, with
a 5mm eyepiece.

Beyond that discussion, focal length of the telescope does limit the maximum
field of view. A 500mm scope with the largest "useful" focal length eyepiece
in a 1.25" barrel gives around 3 degrees true field of view, where the
1000mm focal length telescope will be half as wide a field in that same
eyepiece. In the longer focal length telescope, some of this can be overcome
by going to a larger barrel, a 2" eyepiece, but there is nothing to prevent
you from using a 2" eyepiece in the shorter focal length telescope either,
increasing the 3 degree field even further, out to around 4.5 degrees!

Those Mak's look perfect for planets. Would the EXT 90 fork mount track a
planet well enough to photograph? I can't quite see a heafty camera
riding
on that
thing, so CCD is a thought. Can it track obects such as M31 well enough?

Unlike planets, imaging deep sky objects like galaxies demands a short focal
length telescope. First, to get a wide enough field (as discussed above) to
frame the object (get the whole thing on the film plane), and second to
decrease the exposure time. Decreasing exposure time is even more important
for mounts that don't track well. With CCD cameras you can take multiple
short exposures and stack them through software. The "faster" (shorter focal
length) the telescope, the better for this purpose. A mount that can track
accurately for just two minutes, can give excellent CCD results with a fast,
F5, telescope.


Is that Stellarvue Nighthawk any good? Better or worse than the Orion ED?
I sort of like the refractor idea because I can eventually put it on an
accurate mount
such as the cheaper Losmandy or Vixen models.

Refractors _are_ awesome, providing the best performance per inch of
aperture of any design. The decision process in buying one however, is
really a matter of purpose. Understanding what purpose each scope serves
well, is the first step.