I just received a brand new AT60ED today which I purchased hoping to upgrade the guidescope I was using. I like both the build and look of it, and the functionality of the rack and pinion focuser, but I'm having a problem that I've never experienced before with any finderscope or guidescope, namely, reaching focus. I know there have been other discussions about this here, but I couldn't find a sure answer to what I'm experiencing.
First thing I did, as I usually do, was put a 26mm Plossl in it. To reach focus, I had to rack the focuser all the way out and then remove the eyepiece and move it back further outside the focuser till I was able to achieve some semblance of focus. My first thought was, Uh oh.
I then put a 2" nosepiece and T-ring onto my Nikon DSLR and attached that to the focuser in place of the 2"-1.25" adapter. That just barely reached focus with the focus tube racked out the full distance.
This evening I hooked up my ZWO ASI290MM (regular model, not mini) to it and attempted to focus on a terrestrial light miles away. All I could get at maximum rack distance was a huge, dim round light. Could not bring it into focus. And no, in-travel makes it much worse.
So finally I took the scope outside, pointed it at the Moon, and did a rough estimate of the distance needed to come to focus behind the focus tube with the tube racked all the way out, and it was approximately 2-1/2 inches. That's not going to work for me. I was hoping for a solid guidescope that had just a short travel distance to reach focus, as I'm doing all I can to avoid flexure in my system. I was using an Astromania 60mm with a rock solid guiding train, but figured the AT60ED would get slightly better guide star fields and might help improve PHD tracking some, as I'm using it with a 9.25" EdgeHD. (Please no lectures on flexure and using an OAG instead . I tried that and didn't like it, and was getting good images (round stars) with the Astromania. My goal was longer subs.).
So, am I missing something here, or is it just necessary to use spacers to extend the length of the focus tube? If that's the case, I guess I made a mistake.
Thanks for any help or advice.