Autofocusing in the sequencer

[Rudi]

ZWO is about to release their auto focuser, ZWO EAF, very soon (I think you can already buy it directly from ZWO).

https://astronomy-imaging-camera.com/product/zwo-eaf

So I was wondering, is it possible to include auto focusing in the sequencer, for example between each filter shift?
As far as I can deduct from AA7 and the help file, it is only possible to set focuser position.
I have no experience with auto focusers what so ever, but I fear, that setting the position will no be sufficient, if there's backlash in the focus system.

Alternatively, I could probably script my way out of this?

[fabdev]

Hello, yes, autofocus in the sequencer was added in Service Pack 1, (as an unofficial feature), see the quicknotes.pdf here: viewtopic.php?f=2&t=417

[Rudi]

Thanks Fabio. I missed that.
So setting focuser position to 99999 in AA7 SP1 means autofocus?

Can’t wait to get a ZWO EAF and try it out!

[fabdev]

Yes.
Before using autofocus in sequences, just remember to set the parameters in the new autofocus window, and test them one time manually. As written in the docs, it's also important to set the best binning (the one the gives a pixel size of 15-25 microns).

[Rudi]

Thanks.

How does AA do the autofocusing? Does it take a picture and look at some stars FWHM, and then try to minimize them taking more pictures (V-curve)?

[fabdev]

Hi,
it takes a sequences of images (user defined, for example 5, 7, 9) and calculates the V-curve from them.
For example, for 7 images, the focuser is moved backward for 3 "steps" and then moved forward for 7 "steps", so that 3 images are taken backward, 1 at the original position and 3 forward, all in the same "direction" to avoid backlash problems.