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?
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?