How to find best manual focus settings? - General Help and Assistance on using CHDK stable releases - CHDK Forum
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How to find best manual focus settings?

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Offline Elbourne

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How to find best manual focus settings?
« on: 01 / February / 2021, 09:41:40 »
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I am running chdkptp on a Raspberry Pi 4 connected to a Cannon PowerShot Elph 180. I am using the set up as a book scanner.

How can I go about determining the best manual focus settings for the best quality image?

shoot -u=<s|a|96> -tv=<v> -svm=<v>





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Offline c_joerg

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Re: How to find best manual focus settings?
« Reply #1 on: 01 / February / 2021, 12:17:06 »
Why not autofocus and then lock?

When you capture in JPG, the largest image size is the sharpest. You just have to take the largest picture.
I do this with my manual lenses with a script.
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Offline Elbourne

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Re: How to find best manual focus settings?
« Reply #2 on: 01 / February / 2021, 18:00:42 »
Quote
Why not autofocus and then lock?

I guess what I am asking then is, how do you do that with chdikptp? :)
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Offline reyalp

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Re: How to find best manual focus settings?
« Reply #3 on: 01 / February / 2021, 18:29:17 »
Quote from: Elbourne on 01 / February / 2021, 18:00:42
Quote
Why not autofocus and then lock?

I guess what I am asking then is, how do you do that with chdikptp? :)
Code: [Select]
set_aflock(1)
should do an AF scan and lock focus.

Alternatively, you could get the camera autofocus distance using
Code: [Select]
=press'shoot_half' repeat sleep(10) until get_shooting() return get_focus()
And then pass the value to your shoot commands with the -sd=<number>mm option.

Or you can use
Code: [Select]
=set_mf(1)
and adjust the focus with set_focus until looks good.

If you trigger your shots with rsint command, half press is held between shoots, so all settings will be kept the same.

For your rig, you may be able to find the best focus distance once (perhaps starting with AF as described above, and then tuning with jpeg sizes if needed) and then just use that value every time you use it, at least when you aren't doing books that several inches thick. Cameras like the elph180 have a pretty large depth of field, and relatively coarse focus adjustment. [/code]
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