I got a telescope a few years back and though it works well for
looking through with human eyes, it's been close to impossible
to use with with a digital SRL camera mounted at the eyepiece.
The problem is that the camera body can't move close enough to
the tube to obtain focus on objects futher away than about 20
metres. Of course, that's not very useful for a telescope
(unless you'e into bird-watching). The camera can be made to
focus with the addition of a barlow lens, but the only one of
those I have magnifies by a factor of two and adds some
blurring, so that's not really an ideal solution either. What I
really want is to put the camera at prime focus using only the
primary and secondary mirror. On one of my bi-annual google
searches for a solution I stumbled across the suggestion of a
Hubble style operation to mount the telescopes primary mirror a
bit closer to the secondary mirror, so making the focal plane
move a bit further away from the tube. However, the original
post is rather low on detail.