AstroImager autofocus failure stops a Sequence

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rumen
Posts: 156
Joined: Wed Feb 22, 2017 7:31 pm

Re: AstroImager autofocus failure stops a Sequence

Post by rumen »

Hi elmore
elmore wrote: Wed Oct 27, 2021 2:51 am AstroImager 625.

I was unable to get the RMS Contrast to stick. As soon as I started a sequence or manual autofocus the selection went back to Peak/HFD. I went directly to the indigo server within AstroImager and set RMS contrast in the Imager Agent > Agent and set RMS contrast and saw it became set in AI, but as soon as I manually started autofocus (or ran a sequence with an autofocus) the selection reverted to RMS Contrast.
This is something related to AstroImager and Peter should look at this.
Focus was on occasion too far off initially for radius of 8 to converge (previously I was using 20). If starting from near focus, 8 was reliable.
Yes, this is expected behavior. This is a limitation of HFD you should start from a relatively close focus in order to have a measurable HFD. RMS works fine with very out of focus images.
There was an autofocus failure shown in the attached log. Focus appeared to be converging to a good focus when the Failed to reach focus, restoring initial position error occurred. The focuser did return to what looked like the initial position.
Yes, this happens when focus exceed some limit of 10 * Initial step distance from the original position. If "return t the original position" was disabled the second run would have reached the focus. This is a saafety frature which we have changed now it is 20 * initial step, but still if this happens by default it will return and you will never reach the focus. This is one of the reasons I am so passionate about removing "Return to initial position" as a default behavior, but Peter insists on it...
It would have been better to have been tracking focus quality and gone to the "best" focus.
This is actually what we are doing but best focus is not an accurate number, many hings are involved, like seeing backlash etc...
What I am working on is determining some boundaries of a good focus. Last 2 night we spent testing with a friend of mine and Now i have a good ide when the focus is good or not.
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elmore
Posts: 79
Joined: Tue Dec 04, 2018 2:34 am

Re: AstroImager autofocus failure stops a Sequence

Post by elmore »

Thanks.
I am learning more about how to focus now and look forward to a version that will allow me to use RMS contrast.

Another thought. If focus fails, on the next try make the initial offset in the opposite direction. My scope defocuses slightly differently on the two sides of focus and it might converge from one side but not the other.
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elmore
Posts: 79
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Re: AstroImager autofocus failure stops a Sequence

Post by elmore »

I ran AstroImager 626 all last night.

RMS Contrast now works both manually and in a Sequence.
After learning how to set exposure to avoid the saturation error and determining the correct initial step size, final step size and radius for my filters that are not at all par focal, all two dozen autofocus runs using RMS Contrast converged on excellent focus.

A single bright star in the field seems to trigger the exposure saturation error.
rumen
Posts: 156
Joined: Wed Feb 22, 2017 7:31 pm

Re: AstroImager autofocus failure stops a Sequence

Post by rumen »

Thank you for the report.

Yes any saturated stars may confuse the contrast estimator that is why we issue such warning. I am working on making it more robust when saturation is detected bit it will take time. So far only warning is issued to let the user know that the focus may be reported ok bit in fact it may not be OK.
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