The Sonoita telescope was the original node for AAVSOnet. Back in 2005, John Gross, Dirk Terrell and Walt Cooney approached me to participate in a robotic telescope that they had working down near Tucson. This was a Celestron C14 OTA, an SBIG STL-1001E CCD camera, and a Paramount ME inside of a dome.
We ran the system in that configuration for several years - we eventually called it SRO35. However, Walt and John really wanted something bigger, and in the Fall of 2006, John found a 20" f/4 Newtonian on Astromart. He suggested that we buy it as a group; Dirk and I were a bit suspicious as to whether it would be a good performing photometric telescope, and preferred to leave things as they were. Walt ended up buying the OTA himself, and he and John started working on getting it into photometric shape, starting in November 2006. They did some initial tests on a different mount during early 2007. Those tests highlighted collimation problems with the OTA, requiring redesign of the mirror mounts.
We further tested the OTA on John's Paramount in summer 2008, using an ST-8 camera. Around November 15, 2009, we installed it for AAVSO use on John's Paramount along with an STL-6303E. This configuration is called SRO50. After running with this configuration for several months, we decided that the images were still not good enough, and replaced the 20" with the original C14 on 2010-02-27. Finally, we reinstalled the 20" on 2010-10-19, and that has been the system in place since then.
So there are two periods when SRO50 was running:
2009-11-15 through 2010-02-27
2010-10-19 to current
You can also tell by looking at your images: the SRO35 images are about 800KB compressed; the SRO50 images are about 4.4MB compressed.
The recent images, from 10/19 onwards, have not been released to the observers. I wanted to thoroughly understand the new dark frames, and John has been trying different configurations with the OTA as there were still focus problems in some orientations. However, we have decided to go ahead and let the observers have the images, with the caution that you need to look at each image and see whether its quality is good enough for your use. The images are large (6Mpix, and about 30x40arcmin), but you can trim them down to a managable size and still have a good field coverage; the sampling is much better than with the SRO35 configuration.
The images will start flowing this weekend.