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Shutter and/or aperture override Tv Av mode?

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Offline schnur07

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Shutter and/or aperture override Tv Av mode?
« on: 13 / January / 2013, 02:48:09 »
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I have a Canon SX40 HS and downloaded the CHDK today.  Does the shutter and/or aperture override only work in manual mode? 

If I set the shutter speed to 5 sec in the alt mode, then get out of alt mode and put the camera in Av mode,  in the upper left hand corner it shows TV:5, but when I depress the shutter half way to take the picture, it changes the TV value in decimals equal to the shutter speed chosen by the camera (as if I were in normal camera mode - no CHDK).  If I'm in manual mode, the shutter stays at 5 sec, and I can change the aperture to whatever i want.

Is this how it's designed to operate?  I would think you should be able to alter the aperture in Av mode.
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Offline reyalp

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Re: Shutter and/or aperture override Tv Av mode?
« Reply #1 on: 13 / January / 2013, 03:13:14 »
Quote from: schnur07 on 13 / January / 2013, 02:48:09
  Does the shutter and/or aperture override only work in manual mode? 
No, it should work in auto modes as well.
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If I set the shutter speed to 5 sec in the alt mode, then get out of alt mode and put the camera in Av mode,  in the upper left hand corner it shows TV:5, but when I depress the shutter half way to take the picture, it changes the TV value in decimals equal to the shutter speed chosen by the camera (as if I were in normal camera mode - no CHDK).
What are you trying to accomplish? The definition of Av is that you set the aperture (in the canon UI) to what you want and the shutter is adjusted to give correct exposure. If you set both directly, that would be exactly equivalent to M mode, so why not use that instead?
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Offline philmoz

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Re: Shutter and/or aperture override Tv Av mode?
« Reply #2 on: 13 / January / 2013, 03:30:11 »
Turn off 'Servo AF' in the Canon menu.

Phil.
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Offline schnur07

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Re: Shutter and/or aperture override Tv Av mode?
« Reply #3 on: 13 / January / 2013, 19:54:47 »
Thanks philmoz, that worked.  But am I correct that when you override the shutter using chdk, the camera will not automatically adjust the aperture for correct exposure?  Because that's how it's working for me.
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Offline philmoz

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Re: Shutter and/or aperture override Tv Av mode?
« Reply #4 on: 13 / January / 2013, 20:01:11 »
Quote from: schnur07 on 13 / January / 2013, 19:54:47
Thanks philmoz, that worked.  But am I correct that when you override the shutter using chdk, the camera will not automatically adjust the aperture for correct exposure?  Because that's how it's working for me.

Correct, the CHDK overrides are applied after the camera has calculated the exposure.

Phil.
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CHDK ports:
  sx30is (1.00c, 1.00h, 1.00l, 1.00n & 1.00p)
  g12 (1.00c, 1.00e, 1.00f & 1.00g)
  sx130is (1.01d & 1.01f)
  ixus310hs (1.00a & 1.01a)
  sx40hs (1.00d, 1.00g & 1.00i)
  g1x (1.00e, 1.00f & 1.00g)
  g5x (1.00c, 1.01a, 1.01b)
  g7x2 (1.01a, 1.01b, 1.10b)
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Offline reyalp

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Re: Shutter and/or aperture override Tv Av mode?
« Reply #5 on: 13 / January / 2013, 20:15:46 »
Quote from: philmoz on 13 / January / 2013, 03:30:11
Turn off 'Servo AF' in the Canon menu.
Servo AF disables exposure overrides ? This is probably worth a mention in the notes & wiki page. It doesn't appear to affect tv override on my D10.
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Offline philmoz

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Re: Shutter and/or aperture override Tv Av mode?
« Reply #6 on: 13 / January / 2013, 20:31:09 »
Quote from: reyalp on 13 / January / 2013, 20:15:46
Quote from: philmoz on 13 / January / 2013, 03:30:11
Turn off 'Servo AF' in the Canon menu.
Servo AF disables exposure overrides ? This is probably worth a mention in the notes & wiki page. It doesn't appear to affect tv override on my D10.

Servo AF recalculates exposure as well as focus. Depending on the where the hook calls are being done in the capture task the overrides may or may not get overridden.

Waterwingz found the same issue on his cameras while investigating the USB remote problems reported recently.

Phil.
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CHDK ports:
  sx30is (1.00c, 1.00h, 1.00l, 1.00n & 1.00p)
  g12 (1.00c, 1.00e, 1.00f & 1.00g)
  sx130is (1.01d & 1.01f)
  ixus310hs (1.00a & 1.01a)
  sx40hs (1.00d, 1.00g & 1.00i)
  g1x (1.00e, 1.00f & 1.00g)
  g5x (1.00c, 1.01a, 1.01b)
  g7x2 (1.01a, 1.01b, 1.10b)
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Offline schnur07

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Re: Shutter and/or aperture override Tv Av mode?
« Reply #7 on: 13 / January / 2013, 22:04:11 »
So you're basically in manual mode when using chdk with respect to shutter and aperture. 

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Offline reyalp

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Re: Shutter and/or aperture override Tv Av mode?
« Reply #8 on: 13 / January / 2013, 22:19:02 »
Quote from: schnur07 on 13 / January / 2013, 22:04:11
So you're basically in manual mode when using chdk with respect to shutter and aperture. 
CHDK overrides just set the value you are overriding. For cameras that have a full manual mode, there's little reason to do this unless you need to go beyond the standard firmware limits.

If you wanted to do some kind of custom auto exposure, you can do exposure calculations in script.
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