Jim Cate wrote:
> Thanks for the information. Could you explain what you mean by a
> "barlow+donut"? Could I use one to attach a barlow to my LaserMax
> holographic colimator?
> Jim Cate
A barlowed donut has been expanded from 2x to 3x the size of an
ordinary donut. You'll need a very large mug to dunk it!
Seriously, the donut he is talking about is just a center-spot marker
on the primary mirror. I use one of those notebook paper "reinforcment"
rings you can get in the office supply department. With the barlowed
laser you will see a shadow of this donut shape on the laser face. You
center this shadow by adjusting the primary mirror alignment screws and
then the primary is collimated. It's easier to do than to describe.
Very simple and it seems reasonably accurate for my F/5 scope. I use
the laser in the non-barlowed mode to collimate the secondary.