correction. (How can mfrs. get away with so many short-focus non-apochromats?
Do they have better glass, or are they just putting out color-smudging
rubbish?)

Have you looked through a scope such as the ST-80, 80mm F5? There are some
good reasons why these scopes are popular.

An 80mm F11 scope will have less color but it will also have a limited field of
view. Rather than pushing 80mm to high powers where the exit pupil is too
small to be effective, the ST-80 scopes are optimized for views that are not
possible with larger scopes. A 4 degree FOV at 12.5X is quite interesting and
false color is not an issue.

While these fast scopes are not optimal on planets they will show the rings of
Saturn and maybe even a shadow transit of Jupiter and even the Cassini
division. They are reasonable on double stars as well, on a decent night, one
can split the double-double.



They also make reasonable spotting scopes and bird watching scopes. With a
25mm Plossl an ST-80 works at 16X and a FOV of over 3 degrees, pretty nice for
general use.

Add the compactness of a 14 inch OTA (compared with close to 3 feet for the F11
version) and one has a scope that is easy to transport, easy to find stuff with
and versatile.

They make a good companion for a larger scope and a good travel scope.

I posted about this on 3/12/02 as
"New telescope design?" There were quite a few responses of varying
enthusiasm.

Its been done, one fellow apparently has designed a scope with lenses between
the primary and secondary as well as in the focuser. This is rumored to work
quite well. I owned a 125mm Japanese made refector with a lens between the
primary and secondary. The optics were very poor. Splitting castor was a
major accomplishment.

I currently own an Orion 130mm F5 Newtonian with decent optics, nice sharp
views of Saturn at over 200X, splits all the standard double stars in the 2 arc
second range and with a 2 inch focuser it will do a 3 plus degree FOV.

If one wants to use a smaller secondary, I think the best plan is just to use
one and live with the lesser illumination, after all by lengthening the
effective focal length, one is limiting the FOV.

Rather than being afraid of a fast mirror, I prefer taking advantage of it and
realizing that if the mirror is decent one can have both nice widefield views
and good high power capabilities at the same time.


Jon Isaacs