Auto focus go to best position overshoot amount

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nexusjeep
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Auto focus go to best position overshoot amount

Post by nexusjeep » Sun Jun 09, 2019 4:52 pm

Hi,
I have read the manual in regard to the best focus position and I know that it will go out and come back in if I was focusing from an inward direction. Does anyone know what the overshoot amount is as the backlash on my focuser is 50 microns which equates to 200 steps on the focus motor.

Cheers
Nick

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Re: Auto focus go to best position overshoot amount

Post by admin » Sun Jun 09, 2019 8:34 pm

Hi,

If I recall correctly, it goes to the position that the focus scan started at before then moving back to the best focus position. So, as long as your focus scan started at least 200 steps away from the best position you should be fine. If it started less than 200 steps away then you should be able to manually go to the best position by right clicking at that point on the graph and choosing from the right click menu which include the option to go to the position by going past it and then returning.

Hope this helps, Robin

nexusjeep
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Re: Auto focus go to best position overshoot amount

Post by nexusjeep » Sun Jun 09, 2019 9:28 pm

Cheers Robin,
Sounds fine I usually start more than 200 away so all should be good, if you could just make it dark earlier and the sun come up later + remove the clouds then everything would be great. :D

Thanks
Nick

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Re: Auto focus go to best position overshoot amount

Post by admin » Mon Jun 10, 2019 6:42 pm

I'm told that not buying any new kit is the only thing that has any influence on the getting the clouds to go away. :-)

Cheers, Robin

nexusjeep
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Re: Auto focus go to best position overshoot amount

Post by nexusjeep » Tue Jun 11, 2019 8:38 pm

Hi Robin,
I did not buy any new kit it must of been someone else as :shock: , I have made a geared drive for the rack and pinion focuser as the 10:1 reduction always appears to have a small amount of slippage randomly which is why I converted it to a 25:1 reduction gearbox between the Sesto and the 1:1 side main shaft of the focuser and this gives me approx. 300,000 steps for 80mm of travel as I leave 10mm clear each end and this roughly gives me 0.25 microns per step on the focuser.

Having used a couple of critical focus zone calculators for my scope + filters depending on what I have fitted my CFZ is 80microns to 50microns roughly depending on the items in the optical path. When running an autofocus is there some rule of thumb that can be used based on these numbers to determine the optimum setting within Sharpcap for how many steps the focuser wants to move per measurement when using the autofocus routine to scan through the point of best focuser or is this just trial and error to see what gives a good curve for the calculation.

Cheers
Nick

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Re: Auto focus go to best position overshoot amount

Post by admin » Wed Jun 12, 2019 6:54 pm

Hi, if your critical focus zone is 80 µm wide and you are at 0.25 µm per step in a movement of 100 to 200 steps per measurement point would probably be reasonable as it would get you at least one probably to measurement points in the optimum zone. You may need to go to a larger number of steps if the initial measurement is slow with those steps counts.

Cheers, Robin

nexusjeep
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Re: Auto focus go to best position overshoot amount

Post by nexusjeep » Wed Jun 12, 2019 8:35 pm

cheers will give a go if it ever stops raining and we are above water :D

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