An image of the surprisingly nice galaxy M109, located near Phecda, one of the bright stars of the Ursa Major’s bowl. Imaging was done with the C11, using the Starizona F 7.2 reducer, and the Nikon D750. Unfortunately, the image format setting in SGP was set to “FITS”. That resulted in strange, Black/White images with lots of problems! I could salvage the 27×300″ images a bit but the end result is a bit disappointing, it’s not a color version to start with. ..
After cleaning & collimation, I tested the C11 with the Starizona F 7.2 reducer, the ASI183mm (way oversampled obviously), and guiding using a simple external 8×50 guider and the ASI290MC. Just as a test not bad. I’m not convinced the mirror shift did not have influence in this image. Focusing was a pain, needed to be done manually.
It’s been a while that the C11 was put to use, today I could clean the corrector, and also I found the very very small engraved numbers close to the edge, that line up with the line (and the same number next written next to it) found on the back of the primary. With the tri-bahtinov I could focus and collimate the optics. See also the links here and here.
make sure the three area’s of the mask line up with the three collimations screws of the secondary. The procedure is to focus like a normal bahtinov (ate least one set of lines), and then to look for the area (one of three) where the central line is not nicely central between the spikes. That becomes easily visible when covering an area: when that dims or obscures that is the guilty area, and the corresponding collimating screw needs to the turned (very very slightly). You see the effect on the central line. When centralized, repeat for the third area when necessary.
This is really easy, choose a star high in the sky. On the accuracy of thi smethod I have no clue unfortunately.