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How to use LCD preview/histogram in Shutter Override?

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Offline SD800 user

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How to use LCD preview/histogram in Shutter Override?
« on: 12 / September / 2008, 23:23:47 »
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Hi all,

I just installed Allbest on SD800. The first thing i experiment is shutter override, I found that in this mode what's display on the LCD preview is totally different from the final result (result either over/under exposed). The live histogram is also not useful as it seems to rely on the LCD preview data. Is proper exposure in shutter override only be done with trail and error (by manually adjusting ISO or ND filter value?)

ALso , Is there a semi-auto shutter priority mode for SD800?

Many Thanks,
RC
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Offline fudgey

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Re: How to use LCD preview/histogram in Shutter Override?
« Reply #1 on: 14 / September / 2008, 04:26:06 »
Quote from: SD800 user on 12 / September / 2008, 23:23:47
I just installed Allbest on SD800. The first thing i experiment is shutter override, I found that in this mode what's display on the LCD preview is totally different from the final result (result either over/under exposed). The live histogram is also not useful as it seems to rely on the LCD preview data. Is proper exposure in shutter override only be done with trail and error (by manually adjusting ISO or ND filter value?)

Shutter speed override really really really overrides it. Canon firmware doesn't know CHDK will override it until a fraction of a second before the shot is taken. So, LCD, histogram, zebra and whatever will all think Canon's exposure is going to be used.

This very same mechanism gives us continuous mode bracketing btw.

As for trial and error... if you track how many ev steps you are overriding the shutter speed, you will know where you'll approximately land. Ev compensation can be useful for checking things up to 2 ev (or 4 ev if overrided using a script).
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Offline SD800 user

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Re: How to use LCD preview/histogram in Shutter Override?
« Reply #2 on: 14 / September / 2008, 23:31:46 »
Then a OSD display of the canon's auto shutter speed would be very useful in this case to judge the required compensation. (SD800 doesnt display shutter speed higher than 1/15 sec)

But if CHDK can read the camera determined shutter speed, the difference between that value and shutter override value can be calculated and use the draw an accurate histogram. Has this been suggested before?
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Offline fudgey

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Re: How to use LCD preview/histogram in Shutter Override?
« Reply #3 on: 15 / September / 2008, 12:43:22 »
Quote from: SD800 user on 14 / September / 2008, 23:31:46
Then a OSD display of the canon's auto shutter speed would be very useful in this case to judge the required compensation. (SD800 doesnt display shutter speed higher than 1/15 sec)

Do you mean that while half-shuttering, your camera won't show Tv at all it if it's faster than that?
It will probably quite easy to add a Tv display option to for instance OSD MISC values. Try the feature requests section...

Quote from: SD800 user on 14 / September / 2008, 23:31:46
But if CHDK can read the camera determined shutter speed, the difference between that value and shutter override value can be calculated and use the draw an accurate histogram. Has this been suggested before?

Can't remember... But note that a histogram formed like this will be missing some information (especially when the override is severely different from current LCD exposure) due to areas on the LCD being under/overexposed compared to the resulting photo and that this feature has actually been worked on from a different angle, closely nit with implementing video mode Ev compensation.
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