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ZWO EAF backlash setting

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#1 Barns

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Posted 12 October 2019 - 03:35 PM

Hi all, I've got a ZWO EAF connected up to my Skywatcher Esprit 100 and after some mucking about with the bracket etc think I have it all rigid now. Since it's been (of course) cloudy for ages here I've used SharpCap's contrast-edge-detection autofocus routines to test it out in the daytime pointed at distant stuff.

 

I noticed that if I scanned for focus in the OUT direction vs IN direction, the "Best Position" value found was different by large amounts (~1000 steps) between the directions even though the actual position on the focus tube was the same. So obviously some backlash there and quite a lot of it! I've since re-tightened everything, changed how the bracket is fixed, and remeasured the backlash and now have a value of around 65-70 (still needs some fine tuning measurement). When this is entered into the EAF ASCOM settings, the focus point found is more or less the same in the IN and OUT directions (within ~20 steps), which implies to me that the backlash is now being pretty much compensated for.

 

My question is, is this a reasonable expected value for the backlash to end up at? What kinds of backlash values have other people ended up needing in the EAF ASCOM settings in order to get repeatable focus positions in both directions? Do I need to revisit again the fixings or the possibility that the EAF itself has too much "wobble" internally and needs exchanging?



#2 wrnchhead

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Posted 12 October 2019 - 04:00 PM

That is unusual in my experience. My EAF seems to have none or very little on the Moonlite. Has been repeatable to the last reported digit.
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#3 OldManSky

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Posted 12 October 2019 - 06:50 PM

Mine is at about 25, but it was 40 on my previous scope. Because much of the measured backlash is from the focuser, not the EAF.

#4 Barns

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Posted 14 October 2019 - 06:09 AM

Thanks for the replies. I've spent this morning trying to pinpoint where the backlash is coming from and am coming to the conclusion that it's internal to the EAF unit itself and not with the scope focuser.

 

With the EAF attached (unpowered), I can turn the microfocuser about 1/8ish of a turn each direction until it's stopped by the EAF. With this turning I can see the focus tube immediately go back and forth a little - so I diagnose no backlash between the focus mechanism and the tube (i.e. not on the rack/pinion). However I can see the EAF motor shaft being turned as well whilst I do this little back and forth turn on the microfocuser, meaning the backlash isn't somewhere in the coupling between the EAF and the focus mechanism. Hence I think it has to be internal to the EAF itself; it's allowing a small amount of back-and-forth play on the motor shaft.

 

Does this sound like a "bad" EAF unit? I've read elsewhere that the EAF itself shouldn't have any "play" on the shaft like this.



#5 ThatsMyCoffee

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Posted 16 October 2019 - 08:58 AM

In the EAF unit, it's highly unlikely that there is any play.  I don't believe there are any gears, so where would it come from.  But....  If you think there is, take it off and feel by hand.

 

I'd guess that there is a tiny backlash in the rack & pinion, but a super tiny amount by hand is a HUGE number to a motor like that.

 

In the end...  if it works, just leave it alone.  Adjust your software to compensate and worry about other things.


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#6 OldManSky

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Posted 16 October 2019 - 10:31 AM

The EAF does indeed have gears. There is backlash in any geared train. On my EAF it’s very small, but it’s there.

I have yet to see a focuser that doesn’t itself have some backlash...so the total backlash of the system is a combination of the two sources.

Measure the backlash (ZWO gives one method in the manual, I used NINA’s automated routine), set the amount in the software, and go have fun :)



#7 Hordeck

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Posted 28 November 2019 - 05:44 PM

I have just acquired the EAF focuser and its internal backlash is huge! 1000 steps before it rotates to one or the other direction. My scope focuser has no backlash and my other model Pegasus focuser has no backlash either.

This is very annoying with my preconfigured offset settings between my filters. IDAS filter is offset from Astronomik filters and this is very well controlled with my Pegasus focuser. But now with this EAF on another scope, I have to consider my filter offsets + EAF backlash.

For me this backlash is unacceptable, especially when other brands don't show the same issue.

I can't believe it, it should be a setting or what?



#8 Cfreerksen

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Posted 28 November 2019 - 09:23 PM

I have just acquired the EAF focuser and its internal backlash is huge! 1000 steps before it rotates to one or the other direction. My scope focuser has no backlash and my other model Pegasus focuser has no backlash either.

This is very annoying with my preconfigured offset settings between my filters. IDAS filter is offset from Astronomik filters and this is very well controlled with my Pegasus focuser. But now with this EAF on another scope, I have to consider my filter offsets + EAF backlash.

For me this backlash is unacceptable, especially when other brands don't show the same issue.

I can't believe it, it should be a setting or what?

Ya think maybe it's an anomaly? I am sure all the other reviews that it works well would tip you off. Take it back, it's obviously a defect.

 

Chris


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#9 OldManSky

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Posted 29 November 2019 - 11:30 AM

Ya think maybe it's an anomaly? I am sure all the other reviews that it works well would tip you off. Take it back, it's obviously a defect.

 

Chris

I agree with Chris. My NINA measured backlash on 2 different scopes with the EAF were both under 20 steps...and different, indicating some of the measured backlash was from the focuser. 1000 steps is a huge anomaly...that needs returning.



#10 Willstarnes

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Posted 20 January 2020 - 10:13 AM

I have 120 steps of backlash on my SkyWatcher ED120. There appears to be none in the EAF but mostly in the stock mechanism itself. Have done the EAF setup twice and came within 5 steps of the same answer. 



#11 moonrider

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Posted 20 January 2020 - 08:37 PM

I have no BL with my ZWO EAF, but 24 steps in the ES focuser. Yours is definitely not right.



#12 andythilo

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Posted 27 April 2020 - 02:05 AM

How do you measure backlash in the focuser? I have an EAF and am really struggling with NINA. It will run the AF routine and has a nice graph, but when it returns to the low point, it's way out of focus. I can watch it when it gets to the low point and HFD is like 1.8, but when it returns to that point and I take an image, it's 4+ lol. Clearly a backlash issue. 


Edited by andythilo, 27 April 2020 - 02:05 AM.


#13 OldManSky

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Posted 27 April 2020 - 09:04 AM

How do you measure backlash in the focuser? I have an EAF and am really struggling with NINA. It will run the AF routine and has a nice graph, but when it returns to the low point, it's way out of focus. I can watch it when it gets to the low point and HFD is like 1.8, but when it returns to that point and I take an image, it's 4+ lol. Clearly a backlash issue. 

NINA has a built in routine to measure the backlash. Open the AF tab in the main imaging window, and click the “Measure  Backlash” button. I’ve found it’s best to do it 3 times or so, noting the results, and use the average from the 3 runs as your final value.



#14 andythilo

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Posted 06 May 2020 - 04:16 AM

Well it’s gone back to the supplier. Hopefully I’ll get a new one in it’s place soon.


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#15 artem2

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Posted 23 May 2020 - 03:34 AM

NINA has a built in routine to measure the backlash. Open the AF tab in the main imaging window, and click the “Measure  Backlash” button. I’ve found it’s best to do it 3 times or so, noting the results, and use the average from the 3 runs as your final value.

@OldManSky, That N.I.N.A has a routine to measure the backlash is corect, but I did also buy the ZWO EAF, and when I connect via ASCOM to N.I.N.A then, the option MEASURE BACKLASH is not abailable..

but with my prior FOCUSLYNX EAF, the option to measure backlash was available in N.I.N.A.

 

I am not sure if that is something related to N.I.N.A or to ASCOM DRIVER used??

 

I will get my FOCUSLYNX EAF out again and connect to N.I.N.A version Version 1.10 BETA006 and see if the a routine to measure the backlash is again available and then try same with ZWO EAF.

 

My ZWO EAF has also a HUGE BACKLASH, I had to insert the value 200 in ASCOM BACKLASH settings to compensate it..

 

Cheers

 

Martin


Edited by artem2, 23 May 2020 - 03:36 AM.


#16 OldManSky

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Posted 25 May 2020 - 12:54 PM

@OldManSky, That N.I.N.A has a routine to measure the backlash is corect, but I did also buy the ZWO EAF, and when I connect via ASCOM to N.I.N.A then, the option MEASURE BACKLASH is not abailable..

but with my prior FOCUSLYNX EAF, the option to measure backlash was available in N.I.N.A.

 

I am not sure if that is something related to N.I.N.A or to ASCOM DRIVER used??

 

I will get my FOCUSLYNX EAF out again and connect to N.I.N.A version Version 1.10 BETA006 and see if the a routine to measure the backlash is again available and then try same with ZWO EAF.

 

My ZWO EAF has also a HUGE BACKLASH, I had to insert the value 200 in ASCOM BACKLASH settings to compensate it..

 

Cheers

 

Martin

It's NINA.  The "measure backlash" routine was in the previous nightly builds, but when they went to "beta" on 1.10, it was removed.  The developers felt it was giving inconsistent results, so they removed it while re-thinking it.  They did, however, add a new "overshoot" mode for backlash compensation that appears to work quite well -- I just used it for the first time last week, and I got nice consistent V-curves.

Remember, though, that the 200 value is the backlash of your total system -- EAF *and* focuser.  One of my two focusers on which I have an EAF has essentially zero backlash itself (ok, maybe 1 or 2 steps at the most), while the other has around 7-10 steps.  The EAFs also have a small amount (larger on some than on others).  Since the steps per revolution is 5760, 200 steps really isn't that much (it's about 3% backlash).  And the software can deal with it either using manually entered steps in NINA (I don't bother with setting it in the ASCOM driver), or using the new "overshoot" method.

 

Here's a video that explains the new "overshoot" method...

https://www.youtube....h?v=bc70_iFghQc


Edited by OldManSky, 25 May 2020 - 12:55 PM.



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