Re: focal ratio question
- From: AstroSketcher@xxxxxxxxx
- Date: Sun, 16 Mar 2008 19:54:30 -0700 (PDT)
On Mar 16, 5:40 pm, brucegooglegroups wrote:
The Orion xt 8 is f5.9, and the xt10 is4.7- which is why I posted the
question. The 8 is slightly lighter, but the aperture is smaller, the
focal length is the same for both models.
I could say that the 8-inch would be more likely to perform well at
higher magnifications, or that the 10-inch would be more likely to
perform better on deepsky objects, but I would be guessing based upon
generalities that are not always true. If both scopes were of similar
quality then the 10-inch would be the clear winner for everything, but
as Howard stated, it's more difficult (or it has been in the past) to
fabricate an f/4.7 mirror that's equal in quality to a same sized f/
5.9 mirror.
If I were mostly interested in deepsky observing I would lean toward
the 10-inch. If I were mostly interested in lunar and planetary
observation I could either take my chances with the 10-inch and
perhaps stop the aperture down a little if it helps, or I could go
with the 8-inch and hope for a better quality primary mirror. On the
other hand, if I were primarily concerned with planetary observation I
might consider holding out until I could afford a reasonable EQ mount
as well.
A side by side telescope comparison/review would certainly be
helpful. Perhaps an Internet search would show up some reputable
reviews. Alternatively, perhaps someone reading this thread has
experience with one or both telescopes.
Bill Greer
To sketch is to see.
.
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