Focuser goes way beyond where actual focus needs to be


#1

Hello all,
I have a Moonlite Nitecrawler that I am trying to get auto focusing working on. All my set up is in a remote location right now, however, I do have software assisted focusing (another software that can achieve that). I get it focused using this another software and I know that the focus is excellent. I use the focuser position from that software and use that as my at focus position in SGP. I then use SGP to find out HFR and other components (step size, HFR and star size) required by SGP to get auto-focus working and have them put in the auto focusing window. When I start the auto-focusing run, it starts off from where I am currently and tries to get a v-curve going, however, when it does not find stars in the initial few focus points, it moves out to the outward extreme. Not sure how to stop such behavior. Any clues?

Thanks,
Dhaval


#2

I have had something similar when the step size/number of steps combination leads to a focus that is too much out of focus and stars aren’t visible anymore. Try smaller steps and go for two to three times the HFR you get when in good focus. To avoid it stepping out to extreme values you just need to check Disable Smart Focus in the focuser settings. Good luck.


#3

Thanks. I will disable smart focusing next night I have the chance!

Dhaval


#4

So I did take a look at auto focusing settings and noticed that smart focusing was already disabled - so that is obviously not the cause of this. I will have to lower the step size (I am putting in step size of around 900 - guessing that is way too high). Based on Very Good CFZ calculations, it should be closer to 500 - but is that really what the step size needs to be? I am also going to think that the star size has a role to play here. I will continue to stick to star size of 5 for now and maybe bin 1x1 to see if that allows me to pick up enough stars. I am imaging from Bortle1 skies, so hopefully catching stars should not be an issue at all.

Thanks,
Dhaval


#5

In the help file for auto focus it explains how to set the correct step size for the auto focus routine, it is a simple formula. Once I determined the correct step size which in my case was 45, I set that value and it worked. I left the default star size at 6, use the recommended 9 points. I have been using bin 2x2 and get a consistent V curve since it was set up.


#6

Thanks to all that helped, especially “Generator”. It seems the focusing routine finally ran very well all through the night yesterday night/this morning.

I made two changes - not quite sure which one helped (or maybe both did, given that I seemed to have two issues) - the first one was, I changed the step size to 462 (I was using 2 times that number - trying to trick the system and speed things up - my bad). This number comes from the fact that Moonlite Nitecrawlers have a step size of 0.2667 microns and using it with formula for New Critical Focus Zone (NCFZ) which is listed here - (NCFZ / step size in microns). The second thing that I changed was moved back to 1x1 binning. I am guessing this was not helping in star selection - just didn’t have enough stars to calculate HFR. I am still keeping star size at 5. I may change that to 6, but won’t till I see issues and I know those are caused by star size.

Thanks,
Dhaval


#7

Both likely helped…as they’re interrelated. The CFZ (I’ll have to read that doc about the nCFZ) will be larger when binning at 2x2, generally not significantly so, but larger none the less. Also doubling the step size doesn’t speed things up (if anything it moves the focuser more and would take longer). Plus you’ll generally get to a point where stars (blobs at that point) are difficult to detect the edges of.

We generally recommend that your low HFR is 2-3x your high HFR. I hope to do an Auto Focus setup video in the near future and we’re working on a Auto Focus Setup Wizard as well which should help here.

Thanks,
Jared


www.mainsequencesoftware.com