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change shortest shutter speed

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Offline pronvit

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change shortest shutter speed
« on: 08 / March / 2011, 13:57:03 »
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Is it possible to change shortest shutter speed in Auto/P mode? On my A480 it is 1/2000. But if camera is capable of shorter speeds is it possible to make them usable in Auto/P mode?

To make it clear. I've developed special version of chdk for my specific needs (light/exposure meter) and now I need to make shorter shutter speeds automatically selectable to support very bright scenes.
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Offline Microfunguy

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Re: change shortest shutter speed
« Reply #1 on: 08 / March / 2011, 14:27:27 »
Hello and welcome.

I am not sure what you are trying to do.
You can override shutter speeds with CHDK via a menu selection or with a script.
The A480 has a ND filter so you can force it out in bright light and set shutter speed 8x faster.

What sort of scene are you photographung that requires a faster speed than 1/2000 sec ?
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Offline pronvit

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Re: change shortest shutter speed
« Reply #2 on: 08 / March / 2011, 14:46:30 »
When the shutter button is half-pressed, camera calculates required exposure and uses it to show how picture will look with selected exposure. My patch to chdk then takes ev value, computes and displays shutter speeds for all apertures. I will make post with more info about my patch later.

But in very bright conditions when I half-press the button (iso=100 and minimal zoom level), 1/2000 4.5 is displayer in RED in the bottom of the screen because shorter speed is actually required but isn't automatically selected by firmware. Btw, the same for dark conditions - you know, camera won't select speed longer that 1 sec in Auto/P modes.

So I believe there's limit set somewhere in firmware for min/max auto shutter speed that I want to patch. I know arm assembler well but new to dryos development so I just want to know where to search for these limits in the firmware. Or maybe it's already known how to change it.
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Offline Microfunguy

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Re: change shortest shutter speed
« Reply #3 on: 08 / March / 2011, 15:04:42 »
Quote from: pronvit on 08 / March / 2011, 14:46:30
computes and displays shutter speeds for all apertures.

Your A480 does not have an aperture.

Quote
shorter speed is actually required but isn't automatically selected by firmware.

Surprising that the Canon firmware cannot handle your 'bright' scene.

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I just want to know where to search for these limits in the firmware.

i have no idea.

In SDM I do handle the longer shutter speed situation  :-

Code: [Select]
  else if ((mode_get()&MODE_SHOOTING_MASK) == MODE_AUTO)
    {
      if(shooting_get_canon_overexposure_value() < 0)                              // longer exposure needed
       set_camera_tv(shooting_get_tv96()+shooting_get_canon_overexposure_value()); // so increase shutter time
    }
Display Propertycase 103 to see the  overexposure value.
« Last Edit: 08 / March / 2011, 15:40:33 by Microfunguy »
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Offline pronvit

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Re: change shortest shutter speed
« Reply #4 on: 08 / March / 2011, 16:11:59 »
Quote
Your A480 does not have an aperture.

No, you didn't understand. I shoot film and use a480 with chdk+my patch as light meter. So my patch displays shutter speeds for measured EV and all apertures I have on my film camera.


A480 + modified CHDK as light meter by Vit!, on Flickr


Quote
Surprising that the Canon firmware cannot handle your 'bright' scene.

Nothing surprising actually. 1/2000 sec and f/4.5 (at minimum zoom level) is slightly less that 15.5 EV at iso 100. While clear sky with bright snow (conditions I had today) for example is around 16 EV.

Quote
Code: [Select]
   else if ((mode_get()&MODE_SHOOTING_MASK) == MODE_AUTO)
    {
      if(shooting_get_canon_overexposure_value() < 0)                              // longer exposure needed
       set_camera_tv(shooting_get_tv96()+shooting_get_canon_overexposure_value()); // so increase shutter time
    }
Display Propertycase 103 to see the  overexposure value.

Thank you, maybe this will be useful for me.
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Offline yvesson

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Re: change shortest shutter speed
« Reply #5 on: 08 / March / 2011, 16:28:14 »
Hej,
Well my A540 is limited to 1/1250s at F2.6 and this is very annoying ! You easily reach that limit on a bright day and for flying birds I'd want slightly faster speed, and also avoid few washed out pictures in Av mode when I don't pay enough attention.
I've already asked for something like that somewhere and didn't get a really usefull solution. :/
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Offline Microfunguy

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Re: change shortest shutter speed
« Reply #6 on: 08 / March / 2011, 16:47:18 »
Quote from: yvesson on 08 / March / 2011, 16:28:14
my A540 is limited to 1/1250s at F2.6 and this is very annoying ! You easily reach that limit on a bright day

If it is a bright day, just set a smaller aperture.
Your camera goes all the way to f8.

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Offline reyalp

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Re: change shortest shutter speed
« Reply #7 on: 09 / March / 2011, 00:05:31 »
Does the Bv propcase become inaccurate when the camera the scene is too over exposed ? If you not, you should be able to use that directly, without worrying about the cameras exposure setting at all.
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Offline pronvit

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Re: change shortest shutter speed
« Reply #8 on: 09 / March / 2011, 04:38:33 »
Quote from: reyalp on 09 / March / 2011, 00:05:31
Does the Bv propcase become inaccurate when the camera the scene is too over exposed ? If you not, you should be able to use that directly, without worrying about the cameras exposure setting at all.

Yes, but in this case picture on the screen and histogram aren't correct - that's why I want to fix this?

Generally, is it possible to patch something in original firmware, eg. some hard-coded value, comparison and so on?
« Last Edit: 09 / March / 2011, 04:49:33 by pronvit »
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Offline Microfunguy

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Re: change shortest shutter speed
« Reply #9 on: 09 / March / 2011, 05:08:00 »
You would have to find the value.

As far as I know, no one has looked.

That could keep you occupied for a very long time (and still not find it).
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