Locating secondary mirror on Newtonian
- From: renenkel@xxxxxxxxxxx
- Date: 30 Oct 2006 07:42:44 -0800
Hello -- Can anyone tell me where the focal point of a telescope needs
to be in relation to the eyepiece in order for the image to be in focus
when looking through the eyepiece? Does it need to be at the rear
element of the eyepiece? Or somewhere inside the eypiece? Or
somewhere outside the eyepiece beyond the rear element?
The reason I ask is that I am trying to decide where to locate the
secondary mirror on a Newtonian telescope. If I put the secondary
mirror closer to the primary, the focal point will be further up the
focuser tube. However, I would like to put the secondary as far away
from the primary as possible, since then I can use a smaller secondary
and cause less obstruction of precious incoming light. So how far down
the focuser tube can I put the focus and still allow the eyepiece to
"reach" it?
(In case it matters, the main mirror is 13.1" diameter and has focal
length 59.5" (f/4.5). The tube diameter is 16".)
Any help appreciated,
Robert Enenkel
.
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