SharpCap Forums

New scope (refractor), new focuser (MoonLite), nice camera (ASI2600MC - generally set 60 sec @100 gain), seeing 1.75-3 based on nearby remote observatory. All seem to work well with SC 4.
1) What are some "good numbers" from multi-star FWHM focus assist? I'm bouncing between 4.x-5.x. Generally the system finds between10-100 stars across the frame.
2) What is a good initial focus configuration? I use 3-4 seconds at 400 gain. Randomly(!?) playing with gain/stretch/settings changes the score significantly (without me changing the focus). I have read the 4.0 manual...
3) Removing dark from preprocessing doe not seem to help / hurt.
Any starting configuration for DSO focus appreciated.
Have a great year!

I believe the score can change with settings and lower number isn't better than a lower number with different settings. For example, focus with 2 second exposures, gain 200 might result in a focus score of 2.5 at focus position 1234. Then change to 3 second exposures and 300 gain and you might get a score of 3.5 at the same focuser position of 1234. Focus is still dead on but the score is "worse" because you're comparing it to smaller stars from another setting group. You can only compare scores to settings taken with no variables changed.

That being said the best way I have found to nail settings is to

1- Focus with a mask and get dead on, experiment with all your settings without moving the focuser from here.
2- Play with settings to get around 70 to 100 stars constantly over multiple frames.
3- start backing down exposures so auto focus runs quicker

For LRGB filters I use exposures around 3 to 4 seconds and gain around 200. For NB I use 5 to 6 second exposures with a little higher gain. These seem to work on all three of my refractors from a 60mm at F4 to a 130mm at F6. Your gain setting is pretty high and may cause some stars to blow out. I can't remember what the settings for noise and black level are because I have not adjusted them in forever. I don't remove darks for focusing....it works every time without doing it so I've just been lazy. My AF routine has worked really well for well over 2 years so I really don't touch the settings often. I use the 2600mm and 2600mc.

I also always test focus lower on the horizon....if you can autofocus around 30deg or facing a light dome then it will easily auto focus when pointing towards zenith.