December 4, 2019 0

Astronomy & Telescopes : How to Focus a Telescope


So let’s talk a little bit about focusing
telescopes. Whenever you focus a telescope, basically the only thing you’re doing is changing
the facing between the optical elements, whether that be a mirror or a lens or anything in
between. As so there are a variety of ways that telescopes can be focused. So the first
and easiest way to do it is to actually move the eye piece. So this type of telescope called
Dobsonian makes use of what’s called a crayford focuser. This is a very typical type of focuser
for amateur telescopes, very cheap, very efficient. And so all you’re doing as you can see is
moving the eye piece in and out. Okay, so again you’re changing that spacing. The large
telescope that we have here at our observatory makes use of the same type of focusing mechanism.
So I unlock the telescope and then I can change the spacing between the eye piece and the
mirrors. Another way you can focus is to actually move the mirrors themselves. This type of
telescope called Schmidt Cassegrain makes use of that techniques. Here we’ve installed
a little motor focuser to kind of help with fine tune focusing. But the basic idea is
that on the back of the telescope is a small knob, which as you screw that knob it is on
a warm screw that moves the telescope mirror back and forth so again you’re changing the
spacing. This telescope also makes use of that same principle, but instead of moving
the big mirror that sets at the back of the cell, it actually moves the second mirror
that’s up toward the front of the telescope. And again it makes use of a motorized focuser.

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