Hi Ladyhawke,
Here’s how I went about getting my focuser setup and working for the first time. First off you need to understand your equipment. Mine is as follows so your results may, and I’m sure, differ. My imaging train is 8” SCT, followed by Optec TCF-S focuser, Optech Lepus 0.62x focus reducer, Optech Pyxis Rotator, 55mm T-adapter, Atik 383L+OSC camera.
All that being said, the Optec focuser consist of 7,000 steps, midpoint being at 3,500. Given the Lepus 0.62X reducer and the back focus length to camera and my camera pixel count/size gives me an image scale of 0.79”.
1. Load camera information into SGPro as needed including your image scale.
2. Set the focuser to the midway point, in my case it was 3,500.
3. Perform a manual focus so the best focus is obtained with the focuser set at the midpoint. I used Nebulosity to perform this first manual focus. Once I felt I was in reasonably good focus using the focuser on the optical tube I fired up SGPro
4. In SGPro focuser settings I set the following
a. Bin 3x3
b. Exposer time = 5 seconds
c. Data points = 9
d. Step size
1. I started off using 500 for my step size (this will add 2,000 steps to the 3,500 to obtain the first image shot at 5,500 steps with every subsequent shot being 500 less than the previous until obtaining the required 9 data points .
5. I found for the minimum star diameter 4 works best for my setup
6. I crop the image at 10%
Once I have the above loaded into the focuser settings I run the auto focus and watch the graph. It should form a V or U curve with the lowest point on the curve being about 3 or 4 times lower than the highest point. For example if my lowest point was say 2 HFR I’m looking for my highest point to be approximately 6 or7 HFR.
If after the focus run the spread was not big enough I would increase the step size. If the spread was too much I would decrease the step size and rerun. I found for my setup a step size of 325 gives me very good and repeatable results with 9 data points. I’m seeing typical spreads from about 1.5 HFR low to 4 HFR high on a very good V-plot. If your seeing isn’t real great the V-curve might look more like a U-Curve.
One note – the auto focus may actually take more than 9 data points if your steps are set to low and it needs to take additional data point to get enough point to calculate the focus point. Don’t worry about that for now. You can fine tune once you get a better understanding on how your focuser works with SGPro.
Hope this helps,
mahaffm