Last Friday, October 18, I had the day off and the forecast for the evening was clear and mild and not too windy and no Moon until about 11 and in short just about perfect for an evening of astronomy.
I took everything I would need and set up. I did a polar alignment after the initial star alignment so that it would track better. Hooked up the camera and was imaging by 8 PM.
Everything was going good but I quickly realized my images were ugly and could see that I needed to collimate Elf (my 11″ SCT). So I moved to a bright star and using the camera and laptop worked on it for a bit and then tried again. The images were still ugly so I tried a second time and still no good. By this time I may have spent an hour chasing collimation and Elf just wasn’t having any of it. I decided to give up for the night.
Unrelated, I woke up Saturday morning about 3 and by 5 I decided to fashion an artificial star out of an LED flash light and electrical tape and take Elf to the office while it was still dark. I set the artificial star at one end of a long hallway, about 125 feet from Elf and started to work. See the picture on the left below. A year ago, I had performed the same activity and was successful but Saturday was a bust and in fact I made it worse before daylight forced me to stop 90 minutes later. Instead of looking down a tilted cone, the cone was on its side and I could literally see that.
Sunday I set Elf on the kitchen counter and used a Cheshire eyepiece to roughly get things back in order. When I started, the black circle that is the secondary mirror was actually oblong like looking at the inside of a band saw and the central baffle tube was cutting off the primary. An hour of tweaks got those two items back how they should be and I felt it was good enough to take back out under the stars to do a star alignment.
Wednesday was that night. I went to the River Ridge Observatory and worked on it for another 90 minutes or so. I finally got the cone upright and pretty well if not perfectly centered. See the image on the right, yes this is a before and after. The wind was much too strong to do anything else so I headed home.
It’s been cloudy since but today, Friday the 25th, I got the Baader Colli TM Mark III laser collimator that I ordered earlier in the week. It will of course help with a Newtonian but they say it works with SCTs as well. I don’t know how accurate that promise is, most don’t and those that claim to usually cost $300 or more. But I needed one for the new Newt that I’m getting for imaging and for 16″ Molly if nothing else so I did.
I put Elf back on the counter and inserted the laser. The red dot is spread out a bit, due to the convex secondary mirror, and was off to the side a bit. Another 30 minutes of back and forth turning the three screws the smallest amount I could I finally got the red dot in the center. On a Newt, with its flat secondary, the laser dot should remain very small and disappear in the hole in the etched surface. It will be Sunday at the earliest before I can tell if it worked but I am hopeful. Between the five sessions since the 18th, I’ve spent over 5 hours on this. For a while, I was concerned the secondary was out of position and collimation was impossible until that was addressed.
I think I know what happened. Elf has retained its collimation well over the time I’ve had her but I remember a time several weeks back when I was putting her back in her case and the front slipped out of my hand and hit the rigid foam at the bottom. It was foam but it was a fall of four to six inches. I’ve decided to tip the case up when putting her in it from now on. In that way the slipping can’t happen.
