Re: close focus formula
- From: Rich <rander3127@xxxxxxxxx>
- Date: Thu, 08 Nov 2007 07:35:20 -0800
On Nov 7, 9:31 am, Tenifer <tensorsur...@xxxxxxxxx> wrote:
On Nov 7, 9:40 pm, astrophotogra...@xxxxxxxxx wrote:
On Nov 6, 11:40 pm, Tenifer <tensorsur...@xxxxxxxxx> wrote:
Also why
is the maksotuv able to focus at one feet by just moving the
back focus a little bit like an inch??
If that Mak focuses by moving the main mirror then you are changing
the system design by moving it giving it a different back focal
length. If it is focused by just moving the eyepiece then you will
have the same problem as with the refractor.
Alvan Clark
In the SCT (such as Celetron's), one adjusts the focuser
by moving the main mirror, so it means every focusing/eyepiece
combo used would change the SCT to f/10, f/8, f/6 depending
on how the mirror is moved (or focuser adjusted)? Duh.
Tni
But at some point, you are cutting into the main mirror by moving it
closer to the secondary, thereby reducing the effective light
gathering area and resolution.
On some of the old C8s, you could literally place the focus point a
couple feet behind the scope. Using a ft long extension, i was able
to get down to the microscopic level focusing on objects just 10ft
away or so. Definition wasn't the greatest however.
.
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