ETTL and over-exposed


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rty

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Jan 19, 2002
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#1
I know this sounds dumb, but what really caused a shot taken with a flash (Canon 550EX) in E-TTL mode, mounted with off-camera shoe cord 2, and the camera manually set at 1/60 F5.6 to be over-exposed? Is it because of the wrong metering setting? (Center weighted average vs partial vs evaluative)?
 

tomshen

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Feb 20, 2002
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#2
This should be an issue of exposure. Camera meters are not smart enough yet. Although in many cases a good exposure is expected, under difficult conditions (e.g. dark background or large white subject), the meters are likely fooled either wide open with dark background or underexposed with large white subject. That's why we need to compensate flash in the same way as we compensate exposure. Personally I found flash is a challenging topic in photography. Even the most sophisticated system cannot guarrantee correct exposure all the time.
 

#3
AFAIK, Canon metering system for E-TTL is tied to the active focussing point. If you focus on something then recompose, you will get over/underexposure depending on where the AF point is pointing now. Solution is to explicitly preflash before exposure and before you recompose.



Regards
CK
 

rty

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#4
Thanks. It makes sense now. No wonder some shots are OK but some are not.

I just tried the preflash option and indeed it solves the problem.:thumbsup:
 

tomshen

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#7
Originally posted by ckiang


You just have to make sure your subjects does not think that you have ALREADY taken their photo. ;p

Regards
CK
Yes, it IS a problem if I preflash to animals/birds/insects sometimes.
 

StreetShooter

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Jan 17, 2002
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#8
Been there, done that. Aim at medium tone object, preflash to FEL. Then focus, then recompose.

I sold my 420EX and now use the $38 Achiever 260T (tested 4V trigger voltage) at the blue auto setting (lowest). Set shutter speed to 1/200, aim and shoot. No worries, consistent exposure.

And, by the way, when you need slaves, you don't need to worry about an E-TTL preflash screwing up your slave triggers. Of course, you need to cover the on-camera flash with some unexposed slide film. If you need some, pm me and I'll point you in the right direction. ;)
 

tomshen

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#9
Originally posted by StreetShooter
I sold my 420EX and now use the $38 Achiever 260T (tested 4V trigger voltage) at the blue auto setting (lowest). Set shutter speed to 1/200, aim and shoot. No worries, consistent exposure.
This is new to me, can post some results pls?
 

#10
Originally posted by tomshen

This is new to me, can post some results pls?
Reason is simple. The Achiever he used is set in AUTO mode, which is non-TTL. In this mode, the flash uses its own sensor to measure exposure, instead of the active focussing point. This sort of sensor usually measures roughly the whole scene, instead of one small point. So you can actually get more consistent exposures, depending on situation. And of coz, it doesn't pre-flash.

If subject is out of flash sensor range, (very possible if you use flash extenders), exposure will not be accurate.

Regards
CK
 

denizenx

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Feb 1, 2002
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#11
hmm so a vivitar 285 can do the same? since it's auto too...
what's the slide film for huh? block what pins?
 

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