This week I received a CFF250RC (10"). It’s been a long time since I used a compound scope and SGP wasn’t around back then. So I’m seeking advice regarding autofocus parameters in SGP. The scope is 2000mm f/8, and I will also be using it at f/6 (1600mm). I am using a Feathertouch focuser with Optec Quicksync motor that has a step count of 60000. I believe the step size is around 1 micron per step.
For those of you with similar setups, what autofocus parameters do you suggest?
I image with a 10" f/8 Meade LX850 OTA and an Optec Gemini focuser. If you have 1 micron steps, I would start at 250 steps between data points, 9 data points, 2 as the min star diameter; and 2x2 binning, smart focus disabled and 8 sec Lum exposures.
You will want to experiment with 3x3 binning, as well. For me, I needed to increase the number of steps between data point at 3x3 and increased the min star size. At 3x3 the total focusing time was cut by about 20%.
Basically looking for the worst HFR to be about 3x the best HFR. My Gemini has 0.1 micron steps, so I use 2500 steps between data points:
I have noticed that when seeing deteriorates, the V curve is much less precise but might be tweakable with changed parms during poor seeing. So, this is something I plan to experiment with in the near future.
Charlie
Thanks Charlie. I tried to do some focusing last night with many of the
same parameters you suggest. The problem is that I was only getting 1-2
stars in the calculation and the resulting V curve was ugly to say the
least. It did seem to get the focus right though. I tried increasing or
decreasing the min star size to no effect. This is with 5sec exposures,
binned 2x2 on a QHY163M camera, which is pretty sensitive.
I have seen decent V curves with 10 or 12 stars but my feeling is that is near the minimum number to shoot for. I use 15 second exposures for NB subs. The auto focusing routine can consume significant time but that’s a trade off that is well worth it to get well focused frames.
Charlie