Kathy, can you elaborate on your approach to software for synchronizing dome and scope? Are you using a GEM, for example, and is the pier in the center of the dome? Do you program an offset for the tube or is that unnecessary? How often does the dome move while tracking a longer photo session?
It is absolutely essential for any dome control software to know the exact geometry of the mount and scope relative to the centre of the dome. The setup requires that the software know the location of the centre of the mount (defined as the intersection of the RA and Dec axes) relative to the centre of the dome, and the offset of the optical axis of the scope from the centre of the mount. Even with the best construction in the world, you cannot expect the mount to be in the exact centre of the dome. Millimetres matter.
If you are interested in programming your own calculation, you will need to use three-dimensional vector arithmetic to do it. The calculation is not difficult, but you need to be able to visualize the problem completely in three dimensions. There is also a trap built into the ASCOM specification which trips up some commercial software vendors, and is the reason I did my own version.
The way my software works is that it interrogates the mount every ten seconds to determine its hour angle and declination. It uses that information and its knowledge of the mount geometry to calculate what azimuth the dome needs to be at to centre the dome slot in front of the scope. Then, it tells the dome to move. It uses ASCOM drivers to communicate with both the mount and the dome.
I have it set to tolerate a 2-degree difference between the desired dome azimuth and the actual azimuth. The difference changes more or less slowly, as the mount tracks. Once the difference exceeds the 2-degree limit, the dome slews to match the calculated azimuth.
Tracking an object from the northeast across the zenith to the northwest, for example, will produce a very low rate of slews, as the target climbs vertically up the dome slot. As it approaches the zenith, slews will become more frequent. I have seen slews every 30 seconds for targets near the zenith. The rate drops off again as the target descends vertically down the dome slot. This is in effect a digitization of field rotation.
My software is available at: https://www.dropbox....ncV2.0.zip?dl=0
Edited by kathyastro, 24 September 2020 - 02:16 PM.