Can someone answer this question about ETTL vs iTTL/CLS vs PTTL?

Started Oct 25, 2011 | Discussions thread
Graystar Veteran Member • Posts: 8,373
Re: Well, you've given one reason someone would care already.

Matthew Miller wrote:

Nikon and Canon treat flash exposure comp differently.

How so? Plus or minus one EV is still one EV, isn't it?

It’s not flash exposure compensation that’s treated differently. It’s exposure compensation as applied to the camera that gets treated differently.

When you apply EC to a Nikon, that EC is also applied to the flash. This works well indoors because you can adjust your flash exposure the same way you control your ambient exposure. Outdoors, it’s less successful because you are unable to use EC to control ambient exposure. If you want to control your background exposure separately from your foreground exposure, then you must switch the camera to manual mode. But manual mode is difficult in changing light. If you’re in light that’s constantly changing, then you want to use an auto mode for ambient exposure. This results in having to apply a “correction” to the flash exposure compensation. So let’s say you’re in A mode and you want the ambient light underexposed by two stops. You have to set your EC to -2. But now your flash is underexposing by two stops as well. So you have to “correct” the flash by applying +2 of FEC.

With Canon, EC that’s applied at the camera doesn’t affect the flash. So the situation above is handled easily. If you want your ambient exposure underexposed, then you simply apply -2 EC. The flash will continue to provide the same illumination. Of course, indoors, if you want to control your flash exposure then you must always do it through the FEC controls, which usually means either messing with the flash unit or working with the LCD on the camera. Either way, it’s not as effortless as with Nikon, which can be adjusted without taking your eye from the viewfinder.


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