[jenchris (Jennifer)]

Right - this is one I've mastered! I had a helluva time getting it to focus but now I can do it quite quickly if it is altered.

First off, make sure the prism is set up right.
Mine was off kilter so badly that it wasn't even looking through the objective lens properly.
I stripped the thing down and adjusted the prism bearings so that it swung without catching and swung squarely - it was badly set up and jammed so the adjuster was not operating properly.

Do some paper calculations and adding up - the thin lock ring is about 5.5mm the thinnest adjuster is 7mm the slide adjustment is 5mm so you have infinite adjustments to ensure focus is possible. The measurement to both sensors should be the same length from the prism back face.

When you put the thing onto the focuser take off the camera and look through the hole - centring your eye - you should be able to see a light shone at the other end (or daylight if you're sensible enough to set it up in daylight!)

By far the best way of setting up initially is to get the arithmetic right giving yourself a good chance of adjustment on the slide for rough perfection.

Now, in daylight, find a distance horizon. With camera and imager set up in the machine and spooling on the guiding machinery (PHD) and live view on the imager. Adjust focus on the imager to get your horizon focused as a line across the image.
Now you can concentrate on the OAG camera - slide the camera and tube in and out locking off each time to let it settle - it's a dim image and very large compared to the imager. Eventually you should be able to get the line of the horizon focused as a line across your OAG camera.
The rest can be done at night by adjusting the locking ring for the best focus.
Like all things, the first time is thehardest - it took me hours to find the image - now I can do it in seconds -
If you're setting up PHD at night, set up the OAG camera (I use an SSAG QHY5 equivalent) on about 2.5 seconds and make sure you do a set of darks for it