I do a lot of TTL flash shooting of people at events, restaurants, art galleries and hotels. I notice from time to time my cameras exposure performance is not quite right. I have four metering settings within the TTL Flash mode, Digital ESP, Spot, Multi Metering, & Center weighted. I realize each has it's own specific purpose, but given the type of shooting I mostly do what setting should be the most reliable.
The cameras light meter cannot predict flash output so it does not try. I don't think the cameras ambient metering mode has anything to do with flash exposure metering. In TTL the flash pre fires, determines the closest object, assumes this is your subject and calculates an exposure based on that reflectance. It can get fooled just like the cameras ambient meter. Bride by herself, groom by himself and bride and groom together will all reflect different light to TTL.
Think about it. When you shoot outdoors you first meter for the background to establish the ambient exposure. You can either meter the actual sky, ever the persons shoulder or the grass. Once you get the correct ambient exposure then you turn on the flash. You can go manual and use the white towel method, a flash meter or eyeball it and view it after for correct flash output. If you choose ETTL you let the camera calculate then use FEC to adjust flash output.
Indoors, at a dark event if you place your camera on manual and set it to ISO 100, F8 and 1/200 it will more than likely show underexposed. However when the flash fires you get a good exposure. You cameras meter is metering the ambient light and that is why it shows underexposed. Again the flash determines flash output independently of the cameras meter.
If the conditions are right setting the flash on manual is always the best option. If you are in a run and gun situation the TTL is usually needed but will probably required FEC.
I own a Canon so I can't speak for other brands. This is how I understand Canon works.
Zenon Char wrote:
...In TTL the flash pre fires, determines the closest object, assumes this is your subject and calculates an exposure based on that reflectance.
Not exactly. Distance comes into play with some, but not all, lenses in ETTL II flash metering, but in other cases the meter just reads the amount of flash being received. Just as with incident metering, distance isn't really calculated, only light intensity.
That's one reason why having ring USM lenses (which send distance info to the camera) can help make ETTL flash more accurate.
Image1 wrote:
I do a lot of TTL flash shooting of people at events, restaurants, art galleries and hotels. I notice from time to time my cameras exposure performance is not quite right. I have four metering settings within the TTL Flash mode, Digital ESP, Spot, Multi Metering, & Center weighted.
BrianO wrote:
Not exactly. Distance comes into play with some, but not all, lenses in ETTL II flash metering, but in other cases the meter just reads the amount of flash being received. Just as with incident metering, distance isn't really calculated, only light intensity.
That's one reason why having ring USM lenses (which send distance info to the camera) can help make ETTL flash more accurate.
Yeah I did not get into lenses that provide distance information. Thanks for pointing that out. I was just trying to explain that the cameras metering mode has nothing to do with flash metering. It all gets more complex because as soon as you tilt the flash head it stops providing distance information.
It stands for (Electro Selective Pattern) and this is a quote "similar to matrix metering, but with some differences. Intensity in a largish centre area is measured as well as at the edges. If there is a big difference between the two, the exposure selected compensates to make the centre area near middle gray. However, if the exposure is average all over, the selected exposure is more like a centre weighted average"
