How to focus an APM TMB 80 mm f6 Super Apo refractor

When I first acquired this telescope I had difficulty achieving focus either with an eyepiece or with a DSLR. Indeed, to get focus I had to rack the focuser all the way out, pull the star diagonal part way out of the focuser, and then lift the eyepiece a short distance out of the diagonal. All of this then provided a sharp image.

But, this was proving to be a pain in the neck when changing eyepieces. Apart from which I was worried that the eyepiece would fall out when the telescope was slewing across the sky. So, I visited the manufacturer's web site and found that according to the telescope's specifications the back focus is optimised for use with a 2" star diagonal in combination with a Baader binoviewer.

At this time I don't have a binoviewer and I wanted to bring objects into focus with single eyepiece or a DSLR camera body.



I found that the way to do this, is with simple accessories called extension tubes, these photographs show the tubes in situ.



The tubes allow the optical attachments to focus, the eyepiece required a 2" tube and...



...the DSLR needed a 3 1/2" tube.