How to use autofocus with AstroImager/AstroDSLR 4.x

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Peter Polakovic
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Joined: Thu Apr 21, 2016 9:38 am

How to use autofocus with AstroImager/AstroDSLR 4.x

Post by Peter Polakovic »

1. make sure the camera and the focuser is selected,
2. set some sensible exposure time, long enough to make stars visible on even slightly defocused frames
3. select some star near the image center or deselect any previously selected object (and in such case the best star will be selected automatically),
4. set the backlash and the initial and final step values and
5. click the "start autofocus exposure" button in the toolbar.

Note - if you don't know the backlash, set it to 0, it is always better than to set it too high. The initial step size value should be high enough to to make a difference in focus before and after such step. The final step size value should be low enough to make nearly no difference.

Screenshot 2021-03-20 at 13.26.08.jpg
Screenshot 2021-03-20 at 13.26.08.jpg (22.67 KiB) Viewed 318 times
The autofocus algorithm works as follows:

1. capture the initial frame, evaluate the focus quality (combination of FWHM, HFD and peak value) and set the current step size to the initial step size.
2. move one step inwards, capture the frame, evaluate the focus quality.
3. if the last focus quality is better them the previous one, go to step 2 again.
4. clear backlash outwards and set the current step size to one half of its value.
5. if the current step size is equal to the final step size, make one step outwards and finish.
6. move one step outwards, capture the frame, evaluate the focus quality.
7. if the last focus quality is better them the previous one, go to step 5 again.
8. clear backlash inwards and set the current step size to one half of its value.
9. if the current step size is equal to the final step size, make one step inwards and finish.
10. go to step 2
User avatar
Peter Polakovic
Posts: 2691
Joined: Thu Apr 21, 2016 9:38 am

Re: How to use autofocus with AstroImager/AstroDSLR 4.x

Post by Peter Polakovic »

Another guide for imager agent used by AstroImager/AstroDSLR:

https://github.com/indigo-astronomy/ind ... _TUNING.md
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