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Zooming too abrupt, during video recording -- unable to hold focus

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Offline LjL

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Re: Zooming too abrupt, during video recording -- unable to hold focus
« Reply #10 on: 25 / August / 2008, 13:20:58 »
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Weird. The obvious explanation for that is that, in bright daylight, the camera will use a smaller aperture, thus the depth-of-field will be greated, thus the effect less noticeable.
Except in my camera, I can hear no iris noise in video mode - exposure appears to be set purely in software.

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Offline fudgey

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So what you want is almost the opposite of keeping AF locked... you'd like AF to continuously adjust the focus while you're zooming. I don't believe that's possible.

Actually... why not? If camera is in MF mode and user zooms, CHDK could reposition focus to adjust to the same subject distance. The lens characteristics need to be known, but that's either math or table lookup, isn't it? Safety MF could be engaged for a finishing touch by choice.

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Offline LjL

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Re: Zooming too abrupt, during video recording -- unable to hold focus
« Reply #12 on: 25 / August / 2008, 14:16:18 »
But the camera does that automatically already!

It doesn't do it in real time during zooming, though, it only does it after it has finished zooming (or it does it slowly, in any case), which is why zooming video looks ugly.

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Offline fudgey

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Re: Zooming too abrupt, during video recording -- unable to hold focus
« Reply #13 on: 25 / August / 2008, 16:55:26 »
Oh, heh, well, sorry about that one :)

But on topic, changing zoom speed may not be impossible, at least a570is firmware has interestingly related strings such as

ffe080dc GetZoomLensSpeed
ffe83d24 GetZoomActuatorSpeedPPS
ffe83d3c SetZoomActuatorSpeedPPS
ffe86a24 SetZoomLensSpeedMode
ffea4294 SSAPI::ChangeZoomSpeed
ffeb5d14 PT_ChangeZoomSpeed
ffeb6338 ChangeZoomSpeed


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Offline LjL

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Re: Zooming too abrupt, during video recording -- unable to hold focus
« Reply #14 on: 25 / August / 2008, 18:09:30 »
Well, some more advanced cameras do have adjustable zoom spped, so the functions might simply be there for those cameras, and dummies for all the others... but who knows.

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Offline PhyrePhoX

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Re: Zooming too abrupt, during video recording -- unable to hold focus
« Reply #15 on: 25 / August / 2008, 18:19:53 »
imo it is having to do with the fact that for example s-series has 128 steps in the zoom mechanism - more steps, more smoothness. imo

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Offline fudgey

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Re: Zooming too abrupt, during video recording -- unable to hold focus
« Reply #16 on: 25 / August / 2008, 18:53:25 »
Well, some more advanced cameras do have adjustable zoom spped, so the functions might simply be there for those cameras, and dummies for all the others... but who knows.

Well, SSAPI::ChangeZoomSpeed of a570is 1.00e starts at 0xffea42ac, has a great big bunch of code in it and takes a 16-bit halfword argument in r0 if I'm not mistaken...

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Offline fudgey

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Re: Zooming too abrupt, during video recording -- unable to hold focus
« Reply #17 on: 26 / August / 2008, 18:16:38 »
I added a set_zoomspeed command (which calls SSAPI::ChangeZoomSpeed) to ubasic and tested it a bit.

- At wide angle, nothing seems to happen, irregardless of parameter value. Zoom appearst to behave normally afterwards.
- If zoomed in, this function zooms out back to wide angle (and the command also waits while the camera zooms out).

Interestingly, if I am fully zoomed in when calling this function, pressing the zoom in lever will then result in digital zoom (I have digital zoom set to "normal") even though the zoom lense is actually at wide angle.

The same can be achieved by zooming in full optical + zoom in digital and then calling the function. Optical zoom will return to wide angle, but digital zoom will not be altered and can then be adjusted further at will. Optical zoom will start operating after returning to digital zoom 1x using the zoom lever.

So, if nothing else, this is one way to make digital zoom kick in at any of it's steps (i.e. even other than the two allowed by the digital tele feature) when not zoomed in. Why someone would want this is another issue, I believe the digital tele feature is probably enough for most purposes for cameras that have it... after all it's a rarely needed feature, mostly useful for maximizing burst rate).

I didn't notice any change in speed of the actual zooming (neither optical or digital...altough digital zoom speed does change a lot when zooming in dark conditions but that is normal and related to scene brightness).


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Offline LjL

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Re: Zooming too abrupt, during video recording -- unable to hold focus
« Reply #18 on: 27 / August / 2008, 05:56:39 »
I think it can be mildly useful in manual focus mode (kind of more flexible than the standard focusing window).

Didn't you mean optical zoom in the last sentence? On my camera, that is definitely related to brightness (I guess because it takes longer to refocus after a zoom step).

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Offline fudgey

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Re: Zooming too abrupt, during video recording -- unable to hold focus
« Reply #19 on: 27 / August / 2008, 06:44:05 »
Didn't you mean optical zoom in the last sentence? On my camera, that is definitely related to brightness (I guess because it takes longer to refocus after a zoom step).

No, I mean digital zoom. The speed of digital zoom shifing from a setting to another or from 4x to 16x total zoom The camera emulates optical zoom behavior by smoothly zooming in digitally instead of going in the coarse steps allowed for the user. The live view refresh rate is slower in dark, and this affects the speed of digital zoom.

Focus speed has nothing to do with this. When zooming (optical) from 1x to 4x by keeping the zoom lever cranked will not focus until it's at 4x. Not that I didn't do any of this in a script, I only used ubasic for the ChangeZoomSpeed command.

 

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