Best focus settings with SCTs?

Sequence Generator
1

I am using an SCT for galaxy season without an external focuser. I use the Rigel nstep focusing system. What are the best settings to use for proper focusing in SGP?
Are there any tricks to use to get the best out of a not so best system focus-wise?
For example, should the “smart focus” be kept on? Is it better to have bigger step size than with a refractor? Any tips you can share would be greatly appreciated.

Thanks!

2

Hi Stephan,

I have this same setup as yours on both of my Celestron SCT 8" FR x0.63 as well as the Celestron HD11 with FR x.7 . I have backlash set to 500 steps in, 9 data points, 300 steps per data point. I have two cameras, ASI071 and ATIK 383L+ Mono. I use 4x4 binning. I have not seen any difference between focusing at 2x2 or 4x4. my exposures are set to 5 seconds.

I think the two most important are the backlash steps, ensure they are high enough to clear out your backlash, and getting the step per data point in a reasonable range. to low and will not get a good “V” or “U” curve to high you’ll might end up with “dog ears” on each outside data point.

I’ve been using SGP and the Rigel system for over two years and have not had any issues with this setup.

Hope this helps,
Mark

3

Thanks Mark!
I will try those settings.

What about the "smart focus " option? Do you leave that on?

Stephan

4

Hi Stephan,

I have smart focus disabled. I only ever had one problem with the smart focus and that happen while I was asleep. I woke up the next morning and found all of the images from that point on for the night were bad so I stopped using it. I think some clouds moved in during the focus run and since it failed the first focus run it moved the focuser way out and it could not recover, I think the donuts became too big. With the smart focus disabled, if it fails, I believe it will just go back to the last focus point and proceed on from there. Since turning Smart Focus off, I’ve never had any issues with SGP Auto Focus other then sometimes it sees a galaxy core as a star but even at that it doesn’t seem to have much influence on the overall focus.

BTW, I also set the “Crop auto focus frame by:” to 15% and set the “Minimum star diameter at 1x1 (px)” to 6.

Mark