RoboFocus problems

A-P Mach1GTO
Stellarvue SVQ100
ASI1600MM Pro
Optec DirectSync SV focuser
Opten FocusLynx controller/hub
Current version of Voyager, 2.1.4

Due to inclement weather, I haven’t been outside with my equipment since April. At that time I was able to successfully run the V-curve first light wizard after about ten unsuccessful attempts. I do not have the logs for that night. I did eventually succeed in focusing some subs that night but had to abort due to other issues.

Three nights ago, I attempted to focus on a star near M13 with no success. However, I was however able to do so using local field with M13 present. This went on for several subs before I looked at the results. The files linked below include one of those subs, along with the log for that evening. You can see the focus is definitely lacking, but I cannot understand why. Voyager went through the periodic scheduled focusing with this kind of result.

I have confirmed with Jeff at Optec that hardware and step calibration data is correct and properly entered in the FocusLynx Commander setup.

What might I be doing wrong?

Thanks to all,

Hi Eric,

  1. You might consider resetting your RoboFocus parameters and starting over with the first light wizard.

  2. Have you tried adjusting the backlash setting, and have you confirmed that the correction is in the appropriate direction?

  3. Have you disengaged the focus motor and verified that the draw tube slides smoothly?

  4. Does the focuser move appropriately when you command it to move, say, a few hundred steps in or out?

I’ll see what else I can think of. Good luck.

Kind regards,



I have not used the backlash settings at all, but that’s a really good thought. Are there suggestions in Wiki as to how one would begin to determine the amount and direction? The draw tube does slide smoothly when disengaged and I definitely planned on re-doing the wizard again, hopefully on Thursday night.

Thanks for the reply.



I think the direction of backlash compensation should be IN for most setups, since that direction opposes gravity in most scope positions.

To calculate the amount of backlash compensation, move the focuser back and forth by a small amount (just a few steps) with a software control button. Increase the step size gradually until you begin to see movement. That will be your backlash compensation amount. If you cannot detect any, then just set it to a reasonable, small value.

I do not think Voyager will let you adjust the control buttons in this way. You will probably have to use a different program for this purpose.

Kind regards,


I’ll give that a shot. IN seems logical for certain. The FocusLynx commander should work fine for this.

Thanks again.


Hi Eric,

Glenn has made some excellent suggestions.

You can command the Focuser to move manually with Voyager - use the RoboFire Focuser command widget - by default it’s on the right, on the Commands tab:

The <<IN button moves 5 times the number of steps specified for the < (small move IN) button.
The >>OUT button moves 5 times the number of steps specified for the > (small move OUT) button.
The number of steps in a small move is specified in AutoFocus setup, Robofire Configuration:

I haven’t put anything in the Wiki yet about determining backlash. It’s just the number of focuser steps needed for the gears to engage and start moving the focuser again after you reverse direction.

A couple more thoughts:

  • You need a decent night to run the First Light Wizard - i.e., if there are even high thin variable clouds interfering with HFD measurement, it’s going to have trouble establishing a good VCurve, which is the foundation for all the autofocus routines. The fact that you ran the wizard ten times before having success indicates something was not set up right. Do you recall what was going wrong when the wizard was not successful in creating the VCurve? Star too dim, lost, or saturated?
  • You should get things working so you can consistently focus accurately using the autofocus action buttons in the OnTheFly panel before trying to run a sequence with autofocus.
  • Make sure your Optec focuser software is not “fighting” with Voyager by making its own corrections on the fly. Usually this would be temperature compensation or backlash. I would disable those and focus on getting good results with Voyager’s autofocus.

Voyager has great autofocus routines, we just need to get your configuration straightened out :slight_smile:


1 Like

Thanks for your reply, Rowland.

I do not have any backlash or temp settings enabled for the Optec, nor for Voyager. I did notice the command window having that ability but had forgotten about it. Very handy.

I was moving the focuser via software, back and forth 1000 steps at a time, while gently holding the focus knob. There is a slight but distinct bit of play. You can feel and almost hear it take up gear slack. I just used Voyager’s configuration window while holding the knob and found about two hundred 1.14 micron steps of backlash before I could feel movement. That’s not to say my fingertips are picking up all movement or lack of. I suppose I could halve that and start with backlash IN at 100 steps. Do you agree, or have another suggestion?

Under Configuration window’s VCurve Mode tab, the common parameter default is “OUT”. Should I reverse this to IN so as to counteract gravity pull on the focuser and match the backlash compensation setting? As mentioned, the Optec settings are clear, so no conflicts will be present.

Unfortunately it’s been almost two months since the first successful VCurve first light after those first ten tries. I cannot remember what the error text states and for some reason had no logs. I guess they were not enabled. Conditions that night were good, but with our relatively dark skies it’s difficult to determine if those thin clouds, which are common here, were actually there.

I won’t be attempting any sequences on Thursday until I can run the first light wizard without issue.

Thank you again, sir.


Eric so sorry to hear. I dont think is a Voyager problem, because if you tried to do VCurve 10 time and 1 work i think is question of setting or focuser. Usually for 99% of times setting is ok for all user …

I think the problem is in the focuser. I write in italian how to calculate backlash:

Try to translate from italian with google translate.
Now i look inside log and i tell you i found something.
Start to put 100 step of baclash in IN, remove backlash or other compensation in focuser driver.
Not reverse nothing, just check if go lower in step the focuser go in , and if you go higher in step the focuser go out

WHen you do the first light please try to contact me, we can do togheter in remote teamviewer if you can.

All the best

I look in the log … there’s no vcurve in this log.
I see a lot of problem on focus on single star, small inteval of step for position focuser is not respected. You have backlash. Also this happen in local field focus, calculation is correct and cannot produce a wrong focus like image.

Also when you want to do autofocus from onthefly on a star you must point a right focus star with manual action “Autofocus with Voyager acquirestar”. You have choosed “Autofocus @actual position” this mean Voyager doesn’t search and point for a star, just use star for focus in the actual field. You must be lucky to allow Voyager to work to focus in this way.

All the best

1 Like

Leo, I believe I understand the translation. I will try 100 backlash IN within the focuser driver settings, and try from there.

I was going to contact you regarding a remote session but wanted to make sure the basic issues were cleared up before doing so. I’d rather not waste the remote time doing things that could be done ahead of time so as to maximize the use of a remote session. It may be these suggestions will be all that I need, and I will post my results here after (hopefully) Thursday night outdoors.

My thanks to all. I believe I have enough to work through this problem.


Leo, to answer your second post: After last Friday, I spent a lot of time in Wiki and found the proper “Autofocus with Voyager acquire star” setting to be used. I will do so, and thank you for the additional information.


Eric, ask without problem also in private mail or whatsapp. Night time is to much precious in this season.
If I can speed solution for you is a great thing.

All the best

1 Like

Grazie mille, gentile signore.



A huge thanks to all involved in this thread. After considerable work with software and focuser adjustment instructions given to me by Alex at Stellarvue, it was determined that I have well over 200 microns of backlash. Jeff at Optec and Alex both agree that this is excessive for this focuser.

I’ve removed the focuser for shipping to SV tomorrow, accompanied by the Optec focuser. Alex promised it would be returned “dialed-in”.

The input of everyone here enabled me to put together the pieces of the puzzle. Thank you, gentleman. Your customer service, and the experience of everyone here, are invaluable.


1 Like

Thanks Eric, we are happy to help you because first of all we are astrophotographers like you and we know what mean to manage setup issues.

Let us know

1 Like