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Autofocus active during shutter half-press

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Autofocus active during shutter half-press
« on: 28 / November / 2008, 15:06:14 »
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One function I would love to have is if the camera could autofocus while I have the shutter half-pressed. Kind  of like the way higher end DSLRs do it for tracking moving objects. I know autofocus works when the shutter isn't pressed, but it locks in once you half press the shutter. This is not acceptable if you are photographing objects moving towards or away from you in some way.
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Jim Manning
Canon Powershot S5 IS (1.01b)

Re: Autofocus active during shutter half-press
« Reply #1 on: 02 / December / 2008, 14:17:56 »
How should it works? (never used a dslr)
Autofocus  at regular interval or MD autofocus?

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Offline fudgey

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Re: Autofocus active during shutter half-press
« Reply #2 on: 02 / December / 2008, 14:30:31 »
These cameras can't do continuous focus (there's been some advanced talk about custom focus algorithms and the like before, though), so this would have to be something along the lines bongo_bingo says...

I.e. keep focusing until you full press or try to be smart and figure out when there's a need to focus again.

MD is one way to try the latter, but keep in mind that it's never been done outside scripts (well neither has the continuous focus thing, but that would probably be easier to hack) and it's a beast to configure in a thing like this. If such a thing would actually work, maybe a simpler detection from histogram content change could work...?

But a good compromise would be to assign a key to force refocus during half press (the obvious advantage here to "release shutter -> half press shutter" is that this is way faster due to autoexposure being skipped, among other things). This should be pretty easy to do if we know how to force refocus during half press.


Re: Autofocus active during shutter half-press
« Reply #3 on: 04 / December / 2008, 09:51:22 »
Maybe finding a way to integrate MD with the AiAF grid?


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Offline fudgey

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Re: Autofocus active during shutter half-press
« Reply #4 on: 04 / December / 2008, 12:42:26 »
Maybe finding a way to integrate MD with the AiAF grid?

Isn't AiAF only active while idling (i.e. not while half shooting)?. If it is (or if it can be forced on), this could be kind of easy using Digic III if propcase 18 (shoot when face detect boxes change size/position/existence). This would need some experimenting with prop 18 value unless it stays quite static when people only move a little bit.

From wikia http://chdk.wikia.com/wiki/PropertyCase:
Quote
18   RW   Auto-Focus state after half-press (stays 1 if shoot_half is released!) (0 orange, >=1 green)
      (with AiAF=off only 0 or 1, with enabled AiAF or Face the value depends on position & number of AF boxes)

Re: Autofocus active during shutter half-press
« Reply #5 on: 04 / December / 2008, 14:44:31 »
That only reads and writes the status of the focus. It doesn't actually control it.
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Jim Manning
Canon Powershot S5 IS (1.01b)

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Offline fudgey

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Re: Autofocus active during shutter half-press
« Reply #6 on: 04 / December / 2008, 14:57:40 »
That only reads and writes the status of the focus. It doesn't actually control it.

I know. My point was that if that propcase updates its AiAF value during half press (which it probably doesn't), it could be monitored by CHDK and refocus forced on change.

 

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