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Smart flash exposure

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Smart flash exposure
« on: 22 / January / 2013, 08:52:16 »
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SX40HS has a so called "Smart flash exposure" , an ETTL algorithm to automatically set flash power.
I used 2 different external speedlight (270EX,430EX) with very underexposed results when they are used with light bounced on the ceiling.   :(

The old "dummy" ETTL algorithm of the SX10 was better than the new one, pretty good exposures either with direct or bounced flash in auto mode, and it was faster.

I think the SX40  evaluates the focal lenght, the subject distance (a nonsense with bounced light) and ambient light to "fill" the subject with soft shadows; sadly the results at short focal lenghts are so unpredictable that the only solution is going with manual flash, no ETTL. >:(

I've found several forums with people talking about this problem with DSLR cameras like 20D and 5D. They have a "custom function" to switch from "Evaluative" to "Average" flash metering, i think SX40 has the first one and SX10 the second one and we have no choice.
I see that SX50 and other recent cameras have the "smart flash exposure", so i expect they have the same SX40 behavior.

I hope CHDK will do something helpful, like:
  • A one click shortcut to switch from manual to auto flash (short push on flash button?)
  • Show the flash power in misc when it's in FE lock
  • Is there some hidden parameter in the ETTL function to play with? :xmas
    An "Evaluative flash metering" to "Average flash metering" switch would be the best solution to this problem. 
    I think internally there is still the old algorithm because sometimes (try EC=-2 FEC=+1 or high iso indoor shot and listen to your flash) the ETTL suddenly become very quick, like the SX10 is.
  • Replace the smart ETTL function with something else...
Can i help you?
« Last Edit: 03 / April / 2013, 09:35:27 by alberto1x3 »

Re: Smart flash exposure
« Reply #1 on: 18 / February / 2013, 03:27:26 »
Is my post readable? I don't speak english very well so i hope i didn't make too much errors.

A little request: Is it possible to change the ALT button behavior activating the CHDK menu on long press and keeping the original button function on short press?

I would like to have flash compensation/flash level on short press on custom buttom and CHDK menu on long press, is it possible?

Thank you
« Last Edit: 19 / February / 2013, 04:21:00 by alberto1x3 »

Re: Smart flash exposure
« Reply #2 on: 03 / April / 2013, 06:27:52 »
Is it possible to make a "constant light" flash control?
For example: You set you want flash = 1/16 with ISO = 400 and F=4.0 ( and FEC = 0 ).
When ISO = 200 the flash will go to 1/8 , when F=2.8 it will go to 1/32, when FEC = +2 it will go to 1/4.
If you set ISO = 200 and F=2.8 the flash power remains at 1/16.
I think this would be usefull for indoor photography.
« Last Edit: 03 / April / 2013, 09:29:40 by alberto1x3 »

Re: Smart flash exposure
« Reply #3 on: 03 / April / 2013, 10:15:26 »
Is it possible to make a "constant light" flash control?
For example: You set you want flash = 1/16 with ISO = 400 and F=4.0 ( and FEC = 0 ).
When ISO = 200 the flash will go to 1/8 , when F=2.8 it will go to 1/32, when FEC = +2 it will go to 1/4.
If you set ISO = 200 and F=2.8 the flash power remains at 1/16.
I think this would be usefull for indoor photography.
AFAIK,  CHDK has very limited control over the flash power - low, med, high.  So more precise exposure adjustments are not possible.
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