ZWO EAF focuser settings

[Barns]

Hi, got the chance to try out my ZWO EAF for the first time last night between patchy clouds. Sadly, it didn't go very well.

I was trying to get autofocus going in SGP. However it seemed like focus never really changed much whilst it was going through its routine, focus steps of 10. I tried upping the step size to 20 and even 50 and also playing with backlash settings but these didn't seem to help.

If I tell the focuser manually to go miles (like several 1000) away from the rough focus point and then back again, it seems like it moves back and forth accurately, at least by visually inspecting the focus tube on the scope (Esprit 100). But if the EAF is only moving a few (10s) of steps then it doesn't seem to actually move the tube at all.

Does anyone have experience or advice for settings to use with the EAF and SGP?

I also have APT so could try that. I used APT's backlash calculator previously and it said there was basically zero backlash after going through all its routines. But there it's moving relatively large amounts each time.

Frustrating I can only test on rare clear nights! Or is there some way to test in daylight? Does Sharpcap have anything to help?

[RolandKol]

Hi Barns,

I do not have ZWO EAF, I use DYI one.

I use SGP, and can comment on this software only.

1) You need to use 11 or 9 measurement points (you can reduce it to 7 later). Would advise to start from 9 as does not take so long as 11.

2) For the start, use 100 value for the backslash (I do not have any backslash with a direct motor connection to the focuser's shaft, but anyway, I was made to use 100 to make SGP work properly), you will need to learn which way IN or OUT to use (in my case it did not matter).

3) Move your focuser by 1000 or 3000 steps and measure how many millimeters it retracts the focuser's drawtube (do it several times to measure the average), divide the the average figure by 1000 or 3000 accordingly and learn your focuser's travel distance per 1 motor step. Lets say yours is 5 microns.

4) Calculate your telescope's critical focus zone/distance (the distance which focuser can be moved which does not effects the Perfect Focus).  Lets say yours is 50 microns, it means, if you are in the perfect focus, you will remain in it if focuser will move one way by 5 steps, or 25 microns approximately.

This data will let you know, how many steps you can move the focuser manually and stay in the Focus, - in other words, you will understand what exactly autofocuser does.

5) Also, you will need to calculate the SGP step size for 9 Data Points, - this SGP link shows step by step procedure http://mainsequencesoftware.com/Content/SGPHelp/SequenceGeneratorPro.html?UnderstandingAutoFocus.html

(I was made to use a bit larger step size, calculation value was 75, but I got a better results with 100).

6) Seeing... I managed to set all up only in during a good seeing conditions... (I am based in London... sometimes nights are VERY bright....).

I hope it helps!

And yes... it is tricky at first... it takes time to set all up, - but you will be happy at the end 100%

Edited October 10, 2019 by RolandKol

[Barns]

Many thanks for all those tips! Sounds like I have lots of messing about to do yet, which is good, as half the fun is getting complicated bits of kit working...

Seeing probably wasn't helping - bits of cloud going through.

[RolandKol]

And just a remark:

if in your case 10 steps = 50microns, you will not see focuser to move at all! as this distance is the same as the thickness of a human hear

In other words, you need to know what's going on

Edited October 10, 2019 by RolandKol

[Barns]

40 minutes ago, RolandKol said:

And just a remark:

if in your case 10 steps = 50microns, you will not see focuser to move at all! as this distance is the same as the thickness of a human hear

In other words, you need to know what's going on

Very true! Especially in the dark, at midnight, when I'm falling asleep anyway..! Rough guess from memory is that it travelled roughly 31mm for 5000 steps which makes the step size, as you say, round about ish 5microns. I'll measure properly later when I'm near the scope.

[Barns]

So, I've had the chance to play around a little bit more with the EAF this morning. I used SharpCap's edge contrast focus mode to autofocus on distant buildings, which seemed to work quite well. However it's thrown into light what I think is the real underlying problem with the EAF at the moment - the backlash is HUGE.

I've followed ZWO's methodology to measure the backlash - drive the focuser 1000 steps one direction, then use the fine focus adjust buttons to move 10 steps at a time the opposite direction until you see the physical fine focus knob on your scope move. Count how many clicks of the fine focus adjust button it took before the physical focus knob moved, multiply by 10, that's your backlash.

Mine comes out at ~850! Which is higher than the max value you can input on the EAF ASCOM configuration (max is 255). So I can't even compensate for it in software (not that I'd want to leave such an obviously wrong thing alone without fixing it, anyway). You can actually SEE the backlash, if you tell the EAF to move a large distance opposite to where it's just been moving, there's about ~1s delay where the EAF is whirring but no movement on the scope focuser. Seems very wrong.

What might be causing this huge backlash? It's not the scope focuser itself - that moved perfectly back and forth without the EAF fitted - the Esprit 100 focuser is a lovely unit from what I can tell. I believe I've fitted the EAF tightly such that there's no "play" between the motor and the focus shaft. What might be causing this scale of backlash? Is it likely to be something internal to the EAF unit itself? I should note that this is the customer-returned EAF I got cheap from FLO but it does have a guarantee so I'll return if needs be...

Edit: something I forgot to mention, I had understood that with the EAF fitted the focus knob would be held tight i.e. you wouldn't be able to manually focus. This is fine, however, it is not actually held fully tight by the EAF in my case - you can turn the coarse focus knob about 1/5 turn (ish) back and forth before it's stopped by the EAF. I THINK this would roughly correspond to the backlash amount judging by the travel on the focus tube when manually turning the knob this way (NB the tube moves immediately back and forth, no backlash between knob and tube). What fault might this indicate, in the fitting or in the EAF itself?

Edited October 11, 2019 by Barns

[Barns]

Right I've had another go at the fitting of the EAF now. After discussion with FLO it seems like ZWO now recommend using the standard bracket that comes with the EAF to attach to the Esprit 100, rather than the additional "Takahashi bracket" that was advertised as being needed for Esprit compatibility (and which didn't fit very well). So I've used the standard bracket, which does seem more rigid, plus used two worm screws on each of the EAF to flexible adaptor and flexible adaptor to focus rod fixings (previously only used one worm on each, as per instructions, but there are two holes in each position at 90degrees to each other).

Now when I measure backlash I get a value of around 65-70, which still seems quite high to me but at least is possible to set in the EAF ASCOM settings and thus compensate for. When I tested with SharpCap autofocusing, the "Best Position" calculated for both IN and OUT focus search directions ended up agreeing within ~20 units, which is pretty close I thought.

Still, I can feel a little wiggle looseness on the fine focus knob, not being held completely rigid by the EAF, so I suspect this is where this small residual backlash is coming from. Not sure how I can fix that (this wiggle isn't present when the EAF is detached and the Esprit focuser is back to manual - it's smooth and firm both directions with no backlash as far as I can tell).

So, anyone else got EAF backlash measurements to report? Does my value of 65 seem unduly high, or "about right"? Basically I need to know if this is what I should be expecting, or whether this EAF needs returning.

[blinky]

I have one, I think that's about the same backlash as I have in mine - also I never read the instructions but have used all the grub screws as you have, cant see why they suggest not to use 2 each side as its designed for that.  Its a great device, follow the SGP guide on how to set the step size, I also upped it to 9 steps from 7 as well.

[blinky]

Also think my step size is around the same as yours, sure it will all be fine, just make sure everything is tightened and also, you will feel backlash in the fine focus knob, that normal.

[Barns]

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.

[RolandKol]

3 minutes ago, Barns said:

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.

It does not sound good, - for such a price...
However, a slight backslash should not be a major problem, just like @blinky stated... this is why all kind of soft and drivers have the option to compensate it.

On another hand, - just to be 100% sure the motor or it's gears are OK, drop a line to ZWO directly, you will probably get quite a fast reply once you do it on their Facebook page, as they advertise their EAF at the moment.
https://www.facebook.com/ZwoDesignAstronomyCameras/posts/2320136088035601?__xts__[0]=68.ARAi7ml7Ud4HRNjUDrf8B_ysHYbboLDl5_PiLTjTVw-NxJ65O_4_E_v0EGeuXSeu50tCXVFauwIXfk_LvVTRPh2K1F5OjtBErwNi6X4hugzlO014_Lv6lSZQcJL8FY95xGURoJEDzP50OjdafTEEJTTcBGotxrCD5lUDr0wYDryh4xKc3zXBqESS-FLaDl_0RPb9gKrao3l2yDvqBoPNZngEqkxv8kY0ho1sggzyL8JcGt_w22eNH-OgMkuyc4gaJ-2zgapSGFVCgpD6CMEQT3EtG3Lpfc4xuhZS7gpNUqW7GFudVlexYrOu0M75wk2bEMDnrP-QZFcGcEr7zakMKAkj2Q&__tn__=-UC-R

[RolandKol]

Happy new year!
just curious @Barns, any luck?

I hope you have managed to sort it out

[Barns]

On 05/01/2020 at 11:59, RolandKol said:

Happy new year!
just curious @Barns, any luck?

I hope you have managed to sort it out

Hi, thanks for asking, yes I returned the EAF for a replacement, which works far better - reaches focus reliably in SGP without any huge backlash values required. Much happier! Must've been a duff unit before.

[fwm891]

On 14/10/2019 at 12:13, Barns said:

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.

You will 'feel' more movement with no power because you've taken out all the internal resistance to motion the motor is given when it's powered up.

[scotty38]

Old post plus they've not visited the site for over 2 years 🙂

[Sreesha2024]

On 11/10/2019 at 18:41, Barns said:

So, I've had the chance to play around a little bit more with the EAF this morning. I used SharpCap's edge contrast focus mode to autofocus on distant buildings, which seemed to work quite well. However it's thrown into light what I think is the real underlying problem with the EAF at the moment - the backlash is HUGE.

I've followed ZWO's methodology to measure the backlash - drive the focuser 1000 steps one direction, then use the fine focus adjust buttons to move 10 steps at a time the opposite direction until you see the physical fine focus knob on your scope move. Count how many clicks of the fine focus adjust button it took before the physical focus knob moved, multiply by 10, that's your backlash.

Mine comes out at ~850! Which is higher than the max value you can input on the EAF ASCOM configuration (max is 255). So I can't even compensate for it in software (not that I'd want to leave such an obviously wrong thing alone without fixing it, anyway). You can actually SEE the backlash, if you tell the EAF to move a large distance opposite to where it's just been moving, there's about ~1s delay where the EAF is whirring but no movement on the scope focuser. Seems very wrong.

What might be causing this huge backlash? It's not the scope focuser itself - that moved perfectly back and forth without the EAF fitted - the Esprit 100 focuser is a lovely unit from what I can tell. I believe I've fitted the EAF tightly such that there's no "play" between the motor and the focus shaft. What might be causing this scale of backlash? Is it likely to be something internal to the EAF unit itself? I should note that this is the customer-returned EAF I got cheap from FLO but it does have a guarantee so I'll return if needs be...

Edit: something I forgot to mention, I had understood that with the EAF fitted the focus knob would be held tight i.e. you wouldn't be able to manually focus. This is fine, however, it is not actually held fully tight by the EAF in my case - you can turn the coarse focus knob about 1/5 turn (ish) back and forth before it's stopped by the EAF. I THINK this would roughly correspond to the backlash amount judging by the travel on the focus tube when manually turning the knob this way (NB the tube moves immediately back and forth, no backlash between knob and tube). What fault might this indicate, in the fitting or in the EAF itself?

I have same issue.  I have backlash of 450 with C Edge 8.  How to increase backlash beyond 255 in AAP+  Please advise.