New Crayford focuser installed

One of the issues with the EdgeHD telescopes (actually, most SCTs) is that they are notoriously difficult to focus especially when trying to image with them. The reason is simple - focus is accomplished by moving the main mirror up and down the optical tube. Although the mirror can be locked in place once focus is achieved, as soon as the temperature changes the optical path alters a bit and the focus needs adjustment.  You can't do that remotely - you have to go out to the scope, unlock the mirror, go back inside, refocus, go back outside, lock the mirror and then continue. So I haven't been locking the mirror, just refocusing periodically throughout the night.

Another problem is that as you focus in and out the image shifts. This is because the mirror tilts a bit as it moves. And, during the night as the scope alters it's orientation to the ground, the mirror moves as well. All of this makes it hard to keep getting in-focus images during long sessions.

Well, there is a solution, and it's called the CHL 2.5 inch Large Format Crayford EDGE focuser from Moonlite.  This piece of equipment mounts on the rear of the OTA before the rest of the imaging train (OAG, Filter Wheel and Camera). Now the mirror is locked down tight and focus is achieved by moving the drawtube holding the imaging train in and out, much like a standard refractor telescope. No more mirror flop, no more shifting image, just a smooth focus operation.

I purchased one a few weeks ago, and finally got around to installing it on my scope. There were some issues getting the focus point to reach the critical 146mm. Because the Celestron Off Axis Guider I use is so wide, there wasn't a whole lot of wiggle room getting everthing connected, but it's all set up and I tested it a few days ago. And the results are outstanding. Here is a test image of a star field showing the results.

No only are the stars tack-sharp, edge to edge, but the light cone is now almost perfectly centered on the camera sensor (probably a side effect of not using any spacers so now the imaging train is really solid).  The guide camera still needs to be adjusted to support guiding, but I'll do that later this week. I might add that since I didn't have the guide system working, this test image (15x30sec) was unguided! This simply demonstrates the quality of the AP1100-GTO mount that I got back in April.

Once hurricane Isaias passes by (and the water drains) I'll complete the calibration and be ready to image once again - only now with a much better focuser in play.