ZWO EAF backlash changing over time? - Forums

Topic starter

Jul 4, 2022

I image with an Esprit 100 refractor, an ASI183MM camera and a ZWO EAF, using APT for acquisition.
For the last two nights, the automatic refocus during my sequences has done more harm than good.
My hypothesis is that somehow the backlash setting is no longer good, though it was previously perfect.
Have you experienced something similar?
Could it be due to my rotating the focuser body, which is quite handy in the Esprit?
Clear skies!

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dkamen

Jul 4, 2022

Hi Emmanuel,

Backlash is indeed a thing with EAF and it might change and there are tools to measure it, but I doubt the change would be significant in the course of a few days. And anyway backlash simply means the mechanism will have to push or pull a little extra to get where it wants to go, doesn't it? AF is not guiding, you don't really care if changing direction takes 5 seconds more.

Seeing on the other hand is something that can change (and worsen) between or during sessions and negatively affect the sharpness of your image.

I don't do automated but manual focusing. It is not difficult for me to get an HFR of ~1.5 on clear nights which is the best possible with my equipment as measured by NINA. When I get 1.7 and most attempts to fix it lead to 1.9 or even 2.0+ and then a little while later it is impossible to bring it below 1.85 but suddenly one of the images has 1.6 only for the next to have 2.0 without me changing anything, I know it is a night of bad seeing and just disassemble. Note that it is the atmosphere that worsens and not the focusing. You can confirm by looping the camera and zooming in, you will see the stars visibly changing in size and sharpness between progressive subs without you having made any adjustments.

Cheers,
D.

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Haakon Rasmussen

Jul 4, 2022

Hi Emmanuel,

i have had Problems with the APT auto focusing routine lately. Had to use a Bathinov mask. The routine would find the the best focus.

CS Haakon

Emmanuel Valin

Topic starter

Jul 4, 2022

Thanks for your replies.

My FWHM went from below 3 to above 7 from one sub to the other, with the automatic refocus as only changing point.
Definitely a glitch linked to APT or the EAF, probably not due to seeing.
Appreciate if you have some hints.

CS,

Emmanuel

David Moore

Jul 4, 2022

Backlash should not change in a few nights. Have you tried to focus in and note the position. Focus out and do the same. Repeat several times. What happens?Rotate the focusser body. Do the readings change? Is the focusser held tight enough not to move? Is anything loose anywhere in the optical train?

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Andy Wray

Jul 5, 2022

Do you have the [Make final inwards move] tick box checked in the APT settings? It's a good way of removing backlash.

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