Rick sits to view through the 20" F/3 MX telescope - MX stands for "Mike's eXperiment". The 1.25"-thick primary mirror was made by Lockwood Custom Optics.
ON A WARM, sunny afternoon at the Okie-Tex Star Party in late September of 2008, Rick Singmaster and I were discussing the amazing performance of the 16.5" FX with the 17mm Ethos/Paracorr combo (if you haven't already, read the Okie-Tex 2008 article that I wrote for more about this).
We started talking about just how fast a Newtonian telescope could be. At issue were the optical fabrication and collimation tolerances. Could a faster mirror be made to our optical standards and could the telescope hold collimation as it was moved around?
It seemed there was only one way to find out - to actually build one. We were aware of a 25" F/3 telescope that had been built some years before, but we thought it prudent to experiment with a smaller instrument that would require a bit less time and effort to construct.
A couple of years ago I bought some 20" F/3 mirror blanks. They are Pyrex, and only 1.25" thick. I thought about making a 20" classical Cassegrain or R-C with these used as the primary mirror, carefully mounted, of course. I even had two polished out and ready to figure. So, the logical path forward was for me to figure one of these mirrors to a parabola and put it in a telescope. I thought about building my own telescope for a while, but then I decided that my time was better spent making mirrors at that point. Lucky for me I was sitting next to a guy that could built a very good telescope, knew how to collimate it properly, and didn't mind observing from a seated position over the WHOLE sky.
I figured the mirror in late 2008, and shipped it off to get coated. Rick received it in December, and the scope was mostly done at that point. Cold weather postponed the application of the wood finish for a little bit, but eventually it was done, and Rick said he planned to take it out on the next clear night, which was forecast to be damn cold.
I came home from a meeting of the Champaign-Urbana Astronomical Society and noticed that the message light on my machine was blinking. I played it and Rick's voice spoke "Mike, it's Rick, I looked through you telescope tonight. Give me a call." Way to spill the beans, Rick.
So, I called, and to make a long story short, despite a night of bad seeing, the telescope performed reasonably well, giving round stars. Nothing looked too bad, but the seeing was not good enough to say much more than that. The next night of observing followed some collimation tweaks, including squaring the focuser more precisely. At F/3, every little bit is important, and it paid off. Images were even better.
Finally, a decent night came with warmer temperatures. The F/3 was set up next to a 20" F/3.7 that I had recently completed, and the shoothout was underway. Here's a photo of Rick with the 20" F/3.7 FX to the left (Rick's right) and the 20" F/3 on the right.
Rick stands between a 20" F/3.7 FX (left) and the 20" F/3 MX (right)
Basically, in comparing the two telescopes, once the mirrors equalized a bit, the differences in the images were fairly minor, and were evident only upon careful inspection around the edges of the Ethos field. The view at the center was essentially identical, with the thinner mirror having a slight advantage as the temperature dropped quickly.
The following are quotes from Rick, about comparing the two telescopes:
"Very favorable comparison."
"Most of the time you wouldn't know which 20" you were looking through."
These quotes are about the 20" F/3 MX:
"The views are what you'd expect to see in a good telescope."
"This telescope has exceeded my expectations."
"The damn thing is just amazing."
"The (observing) chair is a must, the ladder is not!"
That's it for now. Rick and I will meet at an undisclosed location in Missouri and I'll get acquainted with my new telescope. I'll add more photos here of that event and eventually some photos from Chiefland and the Winter Star Party.
- Mike Lockwood, Lockwood Custom Optics