Sirius is high in the southwest by dark at my location. Last night I had fairly clear skies and decided to try out a new Celestron 6” SCT. In addition to the OTA, I’ve also added a GSO low-profile Crayford focuser for SCTs, so I tested that as well.
As it turns out, the seeing was average, but transparency was horrible due to haziness. The NELM must have been ~2 because I could barely make out Polaris during the alignment process. In fact, I wasn’t even certain that I had aligned on Polaris until the mount slewed to the first alignment star, which happened to be Sirius, and found it okay.
Sirius did not appear as bright this evening as I’ve known it to be, so that confirmed my suspicions about the transparency. I started with a 24 Pan (62x, 65.3') and through the C6, it was nice and stable, with no “boiling” effect. I used the main focus knob and got what I thought to be very good focus via the CCW method. Next, I tried the Crayford fine focus knob and was able to get that little extra tweak to a sharp pinpoint. I barely had to turn the knob to achieve this, but it was noticeable. I was able to see a hint of the first diffraction ring. Next, I swapped out the 24 Pan with an Astro-Tech Paradigm ED 12mm (125x, 28.8'). Again, I used the main knob for course focus, went CCW to fine focus, but then used the Crayford and got that extra little tweak. This extra tweak provides more defined diffraction rings, too. With the Paradigm, I could make out two distinct diffraction rings, which were surprisingly steady. Alas, I was unable to resolve The Pup, though, despite a long observation through the 12mm. I knew approximately where it should be and thought I saw it once with averted vision, but could not repeat that.
I spent about an hour, off and on, trying to split Sirius and The Pup. I didn’t actually expect to do so with the C6, especially when I realized how bad the transparency was. Still, it was a good opportunity to get out and test the C6 and the Crayford focuser for SCTs. The optics are perfectly collimated, with excellent patterns in and out of focus, so nothing bumped in shipping. Unfortunately, the bad seeing conditions prevented me from confirming the scope's magnitude limit. I was unable to see any star dimmer than about mag 6 or 7, which may have also lent to my inability to see The Pup (mag 8.5). The Crayford provided what I hoped it would, better pinpoint focus, but I feel it’s a bit pricy for the results. As little as I had to turn the fine focus knob, I’m satisfied that my normal SCT focus procedure is working well. What little extra I get from the Crayford is probably more suited to AP applications rather than visual.
