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INDI Library v2.0.6 is Released (02 Feb 2024)

Bi-monthly release with minor bug fixes and improvements

Focus backlash issue

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Do you mean like the FWHMEccentricity script in PI?

Not sure, as I don't use PI. I know ASTAP has a feature to show FWHM variation over the FOV, and compute that into a tilt. That's what I was thinking of. Depends of course on detecting enough stars....
1 year 4 months ago #88577

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Replied by John on topic Focus backlash issue

Ah yes...
www.hnsky.org/astap.htm#inspector

The contour map is the same idea as PI, but looks like it does a bit of maths to convert to a "tilt" %. Very nice!
1 year 4 months ago #88596

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Replied by Nigel Dunmore on topic Focus backlash issue

The following website maybe of interest www.astrobin.com/forum/c/astrophotograph...-objective-analysis/

goes on about analysing tilt and back focus using astap
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1 year 3 months ago #88601

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Replied by Thomas Mason on topic Focus backlash issue

A few observations:

I think the overscan/backlash separation is the right move. Allow separate determination of whether the driver or focus routine manages backlash. In my case I have a Nitecrawler which works very well and doesn’t seem to care - it works fine as is with the linear 1 pass routine even if if doubles up somehow. My second rig has an Esatto and the driver backlash seems not to work well, it introduces randomness having it enabled. Linear 1 pass doesn’t even run unless the backlash box is unclicked - this does leave some residual backlash in the system. I think the overscan option in this case might help.

Regarding the ASTAP tilt/backfocus - this is a very quantitative approach to dialing in best possible image. Having an option in the focus routine where you could automatically scan through the focus position unidirectionally while saving the images would be handy. At present you have to monitor and step the focus position then take a 30 second image, step and image etc until you have all the images to load into ASTAP. Specifying a starting point, step size, and number of steps and walking away for 15 minutes or so would be a nice convenience.
1 year 3 months ago #88641

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Replied by John on topic Focus backlash issue

If you turn on Developer->Save Focus Images then when you do a Linear 1 Pass focus run it will save your focus images automatically in a sub-directory in the same place as your log files. The first image until the last but one will be a sweep from out to in. The last one is after it has moved to the point of optimum focus (of course, when we've fixed your problem with the Essato).

I've not done this myself but you should be able to take these images and load into ASTAP.
1 year 3 months ago #88648

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