Telescope Autofocuser Backlash Compensation

[@I_Spaced_Out]

Are you using an autofocuser? If so, let me know which one you're using, and how much backlash compensation you use. Obviously, belt drive systems won't have any (and yes, I'm totally jealous of you have have them)!

[@I_Spaced_Out]

I'm using the Optec Focus Lynx II with the Focus Boss controller. It has nearly 1000 steps of backlash, but to be completely honest, it wasn't designed for my telescopes focuser. it was the closest match they had.

[@kevinnichts1515]

For the ESATTO 3" - Backlash 0.11mm ; 3181 steps

[@I_Spaced_Out]

@@kevinnichts1515 Ouch. I don't know what's worse. 0.11mm of backlash that takes 3200 steps to clear, or 1mm of backlash that takes 1000 steps to clear. I'd be shooting an email to Prima Luce Labs about this to see if this is a defect, or if they have suggestions. If you need help. I know a guy.

[@I_Spaced_Out]

@@kevinnichts1515 wow, you're much more computer technical than I am. Then again, I'm not a programmer like that. I just do database work. Good job figuring all that out! They should pay you a consulting fee for all that effort!

[@pfhawxwell]

Great video thanks, really helped me to identify the user issue of not tightening everything down. Went from a backlash of 1200 to 125. I can now get SGP to auto focus correctly. So once again many thanks. Clear skies!

[@gollondblack6247]

Awesome tutorial Allen! The only one on this that I have found, and very well explained . Thank you. :)

[@I_Spaced_Out]

That's why I made it! I tried to see if anyone had one already out there and I was surprised that it hasn't been covered yet!

[@DarkArtsAstrophotography]

This was good to know and I needed this. I've had my motorized focuser since I got my new scope at the beginning of summer. Not having a clue what I was doing originally, I didn't really manage to get auto focus working right. I would manually focus using SGPs focus tools, and had good (albeit not 100% accurate) focusing. It's only in the last few weeks that I actually went to the Pegasus Astro site and noticed they had a guide on how to set up their focuser in SGP. Since then, it's been great - most of the time. The issue is that I'm using the Pegasus recommended values for backlash compensation vs using actual numbers. Most of the time, it gets me accurate focus, but the odd time it has a really hard time finding that optimal focus. Based on the results I'm seeing on the focus graph when I have issues, I'm pretty sure that's due to backlash in the system that's not being fully compensated for. I'll be trying your technique out this weekend. Hopefully it fine tunes my focuser enough to make it work accurately every time.

[@I_Spaced_Out]

A dead giveaway that you're dealing with Backlash is the focus run in SGP starts off 'flat' then after a few focuser position moves, it begins to form the V-curve. I was having this issue myself at the Eldorado Star Party (the one I kept asking you to come to) and I couldn't figure out why, even after doing the backlash compensation. I had to go into the log file and read each focuser run's log entry to see that I put the backlash compensation in the wrong direction! So make sure you check that value as well!!

[@hacksesh]

Awesome work Allen. Just setting up an autofocuses in SGP right now. Pretty helpful vid, but I thing I'm going to have to order a micrometer now :) Thank you!

[@I_Spaced_Out]

I bought mine at Lowe's

[@cmelton.photography]

Thanks for a great video, I am building an autofocuser for my newtonian, and i will defiantly be using this.

[@I_Spaced_Out]

Keep me up to date on your progress!

[@kevinnichts1515]

Great video, will give it a try 😊 Just got an Esatto and have to deal with an enormous amount of backlash, around 4 times as much as with my DIY autofocuser.

[@I_Spaced_Out]

Wow! So how much backlash did you end up measuring?

[@I_Spaced_Out]

I just heard back from my contacts with PLL. There is a backlash compensating routine that is imminent for the driver. It will handle the backlash on direction changes. That's all the info I have for you.

[@I_Spaced_Out]

A long time ago, I was on AstroBin. I can't remember my login or password any more. Beyond that - I don't really ever publish final works online.

[@antandshell]

Hi Allen, I followed your instructions to the letter. I have a Feather touch foucser coupled with an optect focuser motor . My backlash at most is 0.03 mm and at least is 0.00. so either or could be error. I am assuming I am wasting my time with backlash then. Even if it was 0.02 I don't think that would have any measurable effect? Your opinion please, thanks for the instructions.

[@I_Spaced_Out]

It is totally possible you have a zero backlash system, but as you saw from my video, I don't and many others also do not. A quick test you can do is on a star. Start in focus, and move your focuser in or out just a few steps at a time, say 10. Do this until you see the star change shape, counting the number of moves you make. 5 moves = 50 steps, if you get where I'm going with this. Then, move the focuser back the same number of moves OR steps (you can do one giant move for all 50 steps if you'd like). did the star return to it's original focused size? If yes, you have a zero, or near zero backlash system!

[@RaysAstrophotography]

Brilliant Allen! Was that IN backlash I assume! I will try sometime!

[@I_Spaced_Out]

It was, and that's important to specify in sequence generator pro. I found out the hard way at the Eldorado star party what happens when you Mark it as OUT, when it's really IN.

[@billschlein]

Great video. Thanks for posting it. One clarification question: when you say "repeat this process a number of times..." do you mean just the 50,000 and back to 0 move and measure steps, or the entire process including the initial move to 2000 and sync to 0 to remove the backlash? Thanks!

[@I_Spaced_Out]

It is just the 50,000 -0 and 0-50,000 movements you repeat. The initial 2,000 / sync to 0 step doesn't need to be repeated at all.

[@billschlein]

@@I_Spaced_Out Perfect! Thanks for the quick reply. I used your method to measure the backlash, and determined a good value to enter for Overshoot Backlash Compensation in N.I.N.A. Autofocus worked very well! Thanks again :-)

[@sendhilchinnasamy]

Very helpful video. I have the Optec focuser as well and have been struggling with SGP autofocus. Question - After getting all the averages, did you move your draw tube to zero position or did you leave it at the '2000' steps position?

[@I_Spaced_Out]

Full zero position

[@Moreflying1]

Thanks for the help!

[@I_Spaced_Out]

You're still imaging? (P.S. I used your CGEM DX modification videos a long time ago to troubleshoot some CGEM non-DX issues I was having)

[@Moreflying1]

@@I_Spaced_Out Still imagining. After years of it I decided to automate focusing. I'm trying to sort it out. There's more to it than I thought. I'm using Optec. Just can't get a repeatable focus nailed down yet. It's always just off. Hope that video was of some help. Still have my DX.

[@I_Spaced_Out]

@@Moreflying1 Focusing was such a chore for me until I got my backlash settings sorted out. Unfortunately for me, my Optec focus controller only allows a maximum of 255 steps, but I need close to 1000. For that, I use an override setting in Sequence Generator Pro. Ever since I started doing that, my focus is dead on (provided I don't induce some kind of user error into the process).

[@benc7805]

Excellent Thanks for sharing

[@I_Spaced_Out]

Glad you liked it, and you're welcome!

[@HogarthsAstrophotography]

Did I miss something, after you ran your focuser out 2000 steps to clear the initial backlash.. and the measurement was 11.9mm. You then synced to zero. I’m with you so far.. you then step out 50000. All good, but when you told it to go back to zero, this should be going back to the relative position of 11.9mm out, anything more would be backlash, but you measured 0.97mm, which is 11mm difference from the relative zero position you set. Confused .. Edit. Ah is it because you zeroed out the callipers at the initial measurement stage.. I think that’s what I missed

[@I_Spaced_Out]

Yep, exactly!

[@Nottsboy24]

Nice upload ☺

[@I_Spaced_Out]

Thanks!