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Limit overexposure on A1200

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Offline Digi

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Limit overexposure on A1200
« on: 16 / November / 2013, 18:43:13 »
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Hi, so I own a Canon Powershot A1200 and its processor is too weak for low light / night environments, it slows it down considerably and made me miss some shots...

So, is there a way to limit the overexposure attempt for the camera in previde mode at least ? With or without CHDK, but I do have it installed on my SD card.
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Offline waterwingz

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Re: Limit overexposure on A1200
« Reply #1 on: 16 / November / 2013, 18:50:08 »
Quote from: Digi on 16 / November / 2013, 18:43:13
Hi, so I own a Canon Powershot A1200 and its processor is too weak for low light / night environments, it slows it down considerably and made me miss some shots...
Well,  technically I don't think it's the processor that is too weak. Its the same processor used on all Canon P&S cameras.  However, its a low cost camera and the lens and sensor are also low cost.  So the processor has less information to work with in low light conditions and had trouble locking focus / exposure.

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So, is there a way to limit the overexposure attempt for the camera in previde mode at least ? With or without CHDK, but I do have it installed on my SD card.
You probably want to set the "AF Frame" menu item to "Center"  and the "AF Frame Size" to "Small".  Turn off the "Servo AF" menu seting and enable the "AF-assist Beam" setting.
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Ported :   A1200    SD940   G10    Powershot N    G16
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Offline Digi

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Re: Limit overexposure on A1200
« Reply #2 on: 16 / November / 2013, 20:09:05 »
Quote from: waterwingz on 16 / November / 2013, 18:50:08
You probably want to set the "AF Frame" menu item to "Center"  and the "AF Frame Size" to "Small".  Turn off the "Servo AF" menu seting and enable the "AF-assist Beam" setting.
I already have those exact settings.

But this doesn't only affect focusing, it also affects framerate in preview, how fast it can turn on or off, rate of photos per minute and basically every action you can do with it is slowed considerably down when it's in low light.

Hmm, I could try turning the LCD off, that turns the preview camera off and should make it process a bit faster by not waiting for all those photons...

However is there any compact camera with this processor that has no noticeable delays when just "looking" in low-light ?
« Last Edit: 16 / November / 2013, 20:18:15 by Digi »
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Offline reyalp

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Re: Limit overexposure on A1200
« Reply #3 on: 16 / November / 2013, 20:34:16 »
I would guess the low frame rate is give the live view enough exposure time to make a visible image.

If you used AE lock (should be described in your Canon manual) on a brighter subject it might not do this, but you probably won't be able to see anything in the live view.
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Offline outslider

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Re: Limit overexposure on A1200
« Reply #4 on: 17 / November / 2013, 03:20:35 »
As reyalp said - this slow camera response is due to calculating the live view from very dark scene. Processor has to do many calculation per each frame. The same happens for my sx130 is.

If you know, what is your desired exposure, you can set CHDK exposure override to it, then set very short exposure time in Cannon settings (or set AE on bright object).

You'll lose live view, but camera will become more responsive.
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Offline reyalp

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Re: Limit overexposure on A1200
« Reply #5 on: 17 / November / 2013, 16:30:03 »
Quote from: outslider on 17 / November / 2013, 03:20:35
As reyalp said - this slow camera response is due to calculating the live view from very dark scene. Processor has to do many calculation per each frame. The same happens for my sx130 is.
It's not calculation (IMO) it's the actual exposure time for live view frames. If you need say 1/10th of a second to get a visible image, then the live view can't do more than 10 FPS
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Offline waterwingz

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Re: Limit overexposure on A1200
« Reply #6 on: 17 / November / 2013, 17:08:00 »
There is an interesting "lag" effect in low light.  Move the camera and the image follows about a 1/2 second later.
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Ported :   A1200    SD940   G10    Powershot N    G16
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Offline Digi

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Re: Limit overexposure on A1200
« Reply #7 on: 18 / November / 2013, 11:12:12 »
It tries too hard to lighten up a dark scene when it's really not required... applies high iso and overexposure to the live preview... I don't mind that, except that it slows it down.

The camera's EV adjuster does not affect preview until half-shutter.... or if the EV selection menu is still active, but in that case when I shoot/focus or whatever it swaps between EV adjusted and normal EV and freezes the camera in those transitions for a second or so, which basically makes the opposite of what I want.

EDIT: I updated my CHDK and it seems the glitchy quick EV adjuster was fixed, it no longer triggers camera's menus.

It seems disabled LCD does help a bit, it still has significant pauses after the shot was made, probably because there's more processing involved... but that slight speed does not worth not having the information about how long the exposure will be and how the photo will actually look.


I see some compensation settings in the auto ISO menu in CHDK but I could never get those settings to work for basic stuff like limiting max real ISO, does anyone use auto ISO and knows how to configure it for this camera ?


A bit off topic about a diferent problem... the shutter button has recently been acting weird, most of the time when I half-shutter then decide to shoot it releases focus and re-focuses then shoots, exacly like if I physically release and press fully press it. I think it's a mechanical problem, the button contacts might be dirty or something... but warranty service is pretty far away, is it safe to unscrew it or should I really take it to the service ? "Safe" meaning it doesn't blow up in milions of pieces once I remove the final screw =)
« Last Edit: 18 / November / 2013, 12:56:19 by Digi »
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Offline srsa_4c

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Re: Limit overexposure on A1200
« Reply #8 on: 18 / November / 2013, 15:08:57 »
Quote from: Digi on 18 / November / 2013, 11:12:12
A bit off topic about a diferent problem... the shutter button has recently been acting weird, most of the time when I half-shutter then decide to shoot it releases focus and re-focuses then shoots, exacly like if I physically release and press fully press it. I think it's a mechanical problem, the button contacts might be dirty or something... but warranty service is pretty far away, is it safe to unscrew it or should I really take it to the service ?
I'd recommend the service. That button is IMHO not user serviceable, it either works or not. Additionally, they would notice that the cam was taken apart by someone else.

The only live view mode (not counting movie mode) that retains high framerate in dark is the "fireworks" scene mode (if it's available on your camera). However, you still won't get a correct preview of your photo and, more importantly, you need to override almost all exposure parameters in this mode (ND filter, Tv, maybe ISO). So, it's likely of no use for you.

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Offline Digi

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Re: Limit overexposure on A1200
« Reply #9 on: 18 / November / 2013, 18:40:23 »
Of course, if I open it up I'll void my warranty, I am aware, but I'll see if I can make my way there then.

I do have fireworks scene but it's locked at 2 seconds of exposure, so that's not really useful for normal shooting.

Anyway, thanks for the replies guys, I'll try more random stuff when I get the chance :}
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