Auto Focus with overshoot

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WB91
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Auto Focus with overshoot

#1

Post by WB91 »

Robin,

Would you be able to add an autofocus routine in SharpCap that has step overshoot in one direction to help compensate for backlash? NINA has this feature and it works very well. I assume you know how this works but if you don't, you simply move back say 100 steps before moving forward to your desired position. User will need the ability to type in this desired overshoot distance (above 100 steps is an example) depending on the focuser used. The point is to move the focuser past the backlash before moving in the reverse direction, but overshoot only needs to be applied in one direction I believe. Normal backlash compensation isn't the best way to handle backlash, unless you can come up with a auto backlash compensation tool for forward and reverse direction to get it spot on, but the overshoot method is much more simpler to do and again works really well. Thanks!

Regards,
Bill
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Re: Auto Focus with overshoot

#2

Post by admin »

Hi Bill,

check out SharpCap 4.0, there are two ways to achieve this.

1) You can specify backlash compensation in the focuser settings - SharpCap will track the backlash and the focuser position will behave as if there is no backlash in the system (providing your backlash compensation amount is correct) - see https://docs.sharpcap.co.uk/4.0/#Focuse ... 20Handling

2) The sequencer/sequence planner have autofocus steps that include exactly this type of backlash allowance to ensure that the point of best focus approach (and the focus scan) always run with the backlash eliminated by the use of an overshoot - see https://docs.sharpcap.co.uk/4.0/#Focus and https://docs.sharpcap.co.uk/4.0/#Focuser

hope this helps,

Robin
WB91
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Re: Auto Focus with overshoot

#3

Post by WB91 »

Robin, thanks for the reply!!

It would be better if the overshoot method was done within the focuser settings within File/Hardware/Focuser. This way you don't have to run a sequence to use it. I am trying to do planetary using a filter wheel and at a 9000mm focus length, the focuser steps are very small to get me at prime focus and using regular backlash compensation gives me trouble. I have tested the accuracy within the NINA program using overshoot and the focus is spot on, but NINA isn't designed for planetary imaging. The only way I can get this to work is if I run a sequence within the sequence editor where I tell the focuser to over shot and then come back, but it is a hassle to do this. Could you add this overshoot feature within the focus control as mentioned above? :D
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Re: Auto Focus with overshoot

#4

Post by admin »

Hi,

you can also do this manually in the focus graph if you don't want to use the sequencer. Once the point of best focus is found, right click on it and you get a menu that lets you choose how to goto that point - either directly or to go past by various amounts and then return. That should do what you want I think.

cheers,

Robin
chongo228
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Re: Auto Focus with overshoot

#5

Post by chongo228 »

I've messed with backlash overshoot and it does work. I still use normal backlash compensation because I've dialed in my backlash numbers perfectly and it works for me.

That being said I do agree being able to add overshot in the File/Hardware/focuser area would be easiest and attract more people to SC. There are other ways to do it as mentioned above in the sequencer but a simple overshoot setting would make it easier and new users wouldn't have to peel back the layers to find it. Overshoot is pretty popular and a feature that people seem to love in NINA.

Anyone not sure about overshoot watch this video and skip to around 1:45
https://www.youtube.com/watch?v=bc70_iFghQc
WB91
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Re: Auto Focus with overshoot

#6

Post by WB91 »

I was able to figure out my backlash per the SharpCap manual, not perfect but close. Overshoot within the focuser control would be ideal. Hopefully Robin could add this.

Robin, on another note, can you put a settle time delay in on all your focus plot graphs so it does not count a star size while blurred. so if you move focus position, maybe wait 1-2 sec before reading star size value to prevent bad readings?

It would also be nice if SharpCap had the ability to store flats per filter so when changing the filter wheel position, the proper flat could be loaded.

Also, I have been having one hell of a time platesolving with SharpCap. Half the time I have to open NINA to plate solve for position. Below is a example as regardless of how I stretch the image, even though stars are showing, SharpCap shows no stars detected. Is this a bug?
SharpCap-pic.jpg
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Re: Auto Focus with overshoot

#7

Post by admin »

Hi,

Ok, so running in reverse...

Plate solving not working - check that you haven't used the display stretch function to brighten the on screen image as that stretch is not used by the plate solving - if you are doing that then your stars may be too dark. Second, if you are using Astrotortilla/ASPS/Ansvr, check the 'Sigma' value in the SharpCap settings - if you are getting too few or no stars, turn that value down until you get 20-100 stars or so.

The changing of flats is a nice idea, but probably will not happen soon - you could build somthing like this using the sequencer though.

A good point about the settle time - I did have some code to try to deal with this originally, but the changes to support still mode may have stopped it from working correctly.

Finally on the overshoot control - can you just remind me of which ways to move the focuser you think should obey the minimum overshoot setting - is it just the goto best position, or was it others?

cheers,

Robin
WB91
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Re: Auto Focus with overshoot

#8

Post by WB91 »

Re plate solving, I tried with no stretch and with, didn't touch brightness control. Was using ASTAP, same as what I use with NINA. Not sure why it couldn't detect any stars.

Re Overshoot, you can set it up both ways in NINA. Here is a screen shot. If you choose to over shoot in one direction, say 100 steps in the IN direction, and you are currently at 30,000 step position, if you move the focuser IN to 29,995, it will go in 100 steps to 29895, then back out to 29,995. by doing this, the focuser will essentially always in up moving one direction thus you never have backlash. If you move in the opposite directing (out), there is no over shoot because the actual movement is always OUT, so the focuser will just goes from 30,000 to 30,005. Make sense? You can do this is your sequencer but its a pain in the butt when you have to manually find focus first.

Here is a video showing it work: https://drive.google.com/file/d/1LPdssT ... sp=sharing
SharpCap-pic002.jpg
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How this helps, would be a killer option to have buddy 8-)
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Re: Auto Focus with overshoot

#9

Post by admin »

Hi,

thanks for the further explanation on the ovreshoot idea - I will have a think about the best way to implement that sort of thing (and probably have a play with NINA to check I actually understand what is going on!)

cheers,

Robin
chongo228
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Re: Auto Focus with overshoot

#10

Post by chongo228 »

Overshoot is all the rage with auto-focus these days. I bet some people don't consider SC when they learn it doesn't have the feature. I don't think they would take your auto-focus routine seriously as they view overshoot as a must have feature for reliable auto-focus.
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