Hello.
My focusing system is now motorized with the Moonlite’s high resolution stepper motor. I am not sure how to figure out the step size for this focuser. I have been using random values to check it out and I mostly get a near flat or awkward-looking focus curve.
Anyone in this forum use the same focuser? I would appreciate if you could share your tip on how to figure out the step size.
Thanks a lot.
Farzad
I use the Moonlite on my EdgeHD11. I’m at work right now - if nobody else chimes in before I get home I’ll send you my settings and process to get this set up.
Im using the same but with a 10 inch Newtonian
For Auto Focus I use the following:
Exposure time 6 sec’s
Binning 2x2
Data Points 9
Step Size 40
Backlash compensation (Other):
Direction IN
Step Size 100
Last time I imaged this worked out great but I have no doubt what imaging train the moonlite is hooked up to will make differences to the main step size. There is a little formula in SGP’s manual which gets you some way close to where you need to be but then the experimentation begins.
Good Luck
Paul
Checking my telescope PC, I use the following on my EdgeHD11:
Exposure time: Varies based on filter (Lum: 5 sec; RGB 10 sec; NB 20 sec
Binning: 2x2
Data Points: 9
Step Size: 70
No backlash compensation (not needed with the moonlite)
I found the travel of the drawtube to be about 17.7mm. With the moonlite’s total step range of ~4355 steps, that makes 0.004064mm/step. You need to place the sweet spot of your scope’s focus (on the EdgeHD it is 146mm) about or near the center of the travel. Then it’s experimentation to get it dialed in.
Have a Moonlite stepper too. Excellent focuser and motor. Really depends on your setup in regard to setting up a nice V curve etc. so follow the SGP manual on this. It really works well and saves time guessing 
My old Rigel system had 75 step increments, the Moolite is 28 … very different
Thanks, Paul, for sharing.
Thanks for sharing. I am assuming you arrived at the step size by trial & error?
Thanks for sharing. So you have good results with 28 as step size? On what OTA?
Basically yes. Step sizes that are too small will cause a shallow/flat curve, and make it hard for SGP to determine the focus point (min HFR). Too large and the extreme points may cause serious errors with OTAs that have central obstructions (donut images). I just picked a step size that seemed reasonable (40) which turns out to be a drawtube range of 0.16mm) and after looking at the curve, adjusted up or down until I get a nice curve. With my selection of 9 data points I want a fairly steep curve that appears within the inner 7 points.
It would be interesting if this could be simulated per OTA ahead of time somehow before heading to the field. If all that matters is the HFR, can one not build a little board illuminated by some tiny LED lights to simulate various star brightness and set up for a good curve?
My step size is for an 8” f4 Skywatcher Newt
And an ASI 1600MM-Pro camera
Right, thanks.
With my At8rc, I started with a step size of 75, obtained using the procedure in one of the docs. However, at the extremes the stars were small donuts and with an Ha filter I believe fewer stars were used than in the other images so the curve got distorted. Using 50 instead gives a very good curve.
Richard Sewards.
This goes pretty deep into setting up Auto Focus:
https://www.mainsequencesoftware.com/Content/SGPHelp/UnderstandingAutoFocus.html
Long story short you want 7-9 positions (7 ideally) and you want to adjust the step size until your High HFR is 2-3x your Low HFR.
Jared
Thanks, Jared.
Which Moonlite are you using? I have the Nite Crawler, WR25 which is very high resolution. If you try a step size of 40 with this it won’t work. It would barely move. I started off with 1500, and narrowed it down to about 475. I guess what I’m saying is, it definitely depends on the model. There is also some information over on the moonlite page, or give Ron at Moonlite a call if you can’t find what you are looking for.
I use CF 2" and CHL 2.5". They both use High Res Stepper Motor kits (Model STM).