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8 inches is a good planetary size if the
atmosphere is steady. f/4 is somewhat troublesome as is the 1/4 wave
rating. Planetary viewing is the most exacting of the optical system, and
the large obstruction of an f/4, probably 30% of the diameter is a bit too big.
It causes the same loss of contrast as 1/4 wave error even with a perfect
mirror. Now add the reported 1/4 wave and it will not likely deliver
planetary quality images.
Being a newbie, the collimation requirements
for f/4 are stringent, and without lots of viewing experience, you may rarely
collimate it well enough to get the best images. In all it would not make
a good planetary scope.
I am constantly amazed by the detail
available in long- focus newtonian scopes, f/8 and up. I have a 4.25 f/11
edmund scope that is refigured to 1/10 wave. the images are fantastic (tho
dim).
You'd better try f/6 or slower, and a 6"or
8" f/6-10 will be the most usable scope. The short focus scopes are of no
interest to me, generally, too fussy and not planetary quality.
Colin
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