Thanks for the response. I haven’t had any obviously ‘bad runs’ lately, since I’ve been tweaking things. My problem is sometimes that I have too many stars, but folks with an OAG probably have the opposite situation. So I think it would be a good thing for the algorithm to try and discard the star clusters in the spirit of continuous improvement. Maybe it’s as simple as giving us another manually entered parameter, like maximum star size?
In any case, as I’ve been working on bringing up my new QHY600 and filter wheel setup, I came up with a way to calibrate my focus position per filter, and accounting for temperature. For me, my aluminum OTA is quite sensitive to temperature, so essentially the temperature never really stabilizes; even 1 deg C is significant. I made an excel spreadsheet to account for all three variables; the filter, the focus position attained, and the temperature recorded immediately after each focus run. My procedure was to focus each filter in order, LRGB Ha OIII SII, then repeat that cycle 5 times, noting the focus position and temperature after each focus run. There was some small amount of time in between each focus run, but it took several hours to complete.
I made a simple linear fit to the data entered in the orange cells, using the LINEST function in Excel, so I could create an estimate for each filter’s focus position vs. temperature modeled as a straight line, y=mx+b. If you look at the graph, the linear behavior is apparent, at least over this small temperature range. The ‘y’ being focus position, ‘x’ being temperature, ‘m’ being the temperature coefficient (focus pos/deg C) and ‘b’ being the y-intercept. Once I have this simple model, I can plug in a temperature from which I can predict what the focus position would have been IF I had performed the focus at that same temperature for all the filters. In my case, I entered 20 degrees, so I could plug in those predicted focus position values into SGP, now with a level playing field, so to speak. The temperature coefficient was calculated by averaging the ‘m’ from each filter’s linear estimation, so it represents 35 runs worth of data. That number was then entered into SGP, so that it can actively move focus position with temperature for each sub frame, but still perform the autofocus routine at every time or temperature interval that I specify.
It occurred to me afterwards that this whole thing could potentially be automated. I know there is the Temperature Compensation Trainer in SGP, but maybe this method could be added/incorporated, so that a complete filter set offset and temperature coefficient could be done as a one-button operation, auto-populating the necessary fields in the focus setup window. I was guiding the entire time, so if the SNR dropped in PHD, maybe that could be used to flag, pause or reject a focus run?
I’d be happy to share the spreadsheet as well.