Cassiopeia Observatory logo
Last updated: 16 April 2011
Subject:	etx-125 focus shift
Sent:	Thursday, April 14, 2011 19:18:27
From: (
I purchased an ETX-125 last fall and over the winter, without having any
good clear nights for viewing, I religiously tried to learn more about
this great little scope and making any improvements that might be
learned from other users.

One thing that I kept noticing was complaints about FOCUS SHIFT and I
noticed a post from a user that it could be reduced by using a short
section of soda straw over the shaft forward of the focus knob reducing
the "play" in the shaft into the rear of the scope.

I was concerned that the straw might become "lost" inside the scope so
here is what I did.

I had an old FM radio antenna and noticed that one of the sections was
exactly the right diameter to slide over the focuser shaft and slide
inside the plastic hole at the rear of the scope creating a "bushing" to
take up "play".

I flared one end of the antenna section by driving it into the slotted
end of a dry wall screw. Next I cut off about 1 quarter inch of the
antenna tube with the flare, scraped off the chrome plating and put it
over the focuser shaft, pushed it into the rear of the scope, and most
of the focus shift was gone.

The flare keeps the new "bushing" from getting inside the rear of the
scope. A small dab of glue on the outside keeps the "bushing" secured
and a small amount of lithium grease will lubricate the bushing.
Mike here: There are many other articles as well on "image shift" on the Helpful Information: Telescope Tech Tips page.

Go back to the Tech Tips page.

Go back to the ETX Home Page.

Copyright ©2011 Michael L. Weasner /
Submittal Copyright © 2011 by the Submitter