Beginner On camera flash, exposure compensation and flash compensation.

Tom Pinchenzo

Tom Pinchenzo

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Total flash beginner question here, trying to get my head around how exposure comp and flash exposure compensation work together. As I understand it, exposure comp will just act as it usually does and provide you with an underexposed or overexposed image by however many stops you needs. Flash exposure compensation affects how strong the flash is. So if I wanted a shot underexposed by 1 stop with a small amount of fill flash I would set exp comp to -1 and flash comp to -1 or -2. I wouldn’t then end up with an image underexposed by 2 or 3 stops?
 
Ive been reading up on the subject too...my understanding is...

Think of it as two exposures. One exposure for the ambient and one exposure for the flash. If the exposure for the ambient is "correct". If you now adjust the flash exposure it will be independent to the ambient exposure. ie the flash compensation won't be cumulative. It won't add to the existing ambient exposure. If you look at the histogram in your camera you can see if it has changed the exposure.

I find it easier shooting in Manual for the ambient and use ETTL with Flash (if the subject to flash distance constantly changes)
 
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As above, it is easier to think of the ambient exposure independently. A word of caution on “underexposed” - that’s your camera’s meter reading vs grey. If your composition is itself dark or bright then the meter reading won’t necessarily be right for a correct exposure. What sort of scene are you trying to light?
 
I've struggled to understand it myself, but then I've never been one to worry too much about auto exposure, where such things matter. A quick and rough 'test' I just did, shows that changing such settings does result in a bit of underexposure, but I think it would be intereresting to do a series of proper tests with a static subject, to really examine how things are affected.
 
It will also depend on how you are using the flash - if it's the primary light source it will have a different effect to the case where the flash is just to 'fill' the shadows.
 
mike weeks said:
It really depends on the camera system to how that is calculated, some would treat the flash as being based on the adjusted exposure, some are totally independent

Mike
Click to expand...

For Nikon Cameras, out of the box, Exposure Comp affects both ambient and flash exposure, and flash exposure comp only affects flash light. So if you wanted the background darker, but the flash light on the subject to remain the same you would dial in say -1 on the exposure comp, and would then need to put +1 on the flash exposure comp. I understand that on Canon bodies, exposure comp only affects the ambient. This makes more sense to me and happily you can configure Nikon cameras to behave like this too.
 
Scooter said:
For Nikon Cameras, out of the box, Exposure Comp affects both ambient and flash exposure, and flash exposure comp only affects flash light...
Click to expand...
I believe Sony work in the same way as Nikon - any Exposure Compensation affects the overall exposure calculation, Flash Compensation then modifies the relative brightness of the flash.
 
If you need guidance; as above you should let us know what camera system.

but as a rule; I think if flash is your key light, then shooting in M is the quickest way to control the ambient exposure.

then either M flash for static situations or TTL for more dynamic situations is much simpler than trying to 2nd guess and compensate the 2 exposures.
 
Hi all, thanks for your thoughts. It's not straightforward, is it, no matter how it's explained! I think I just need to play around. By the sound of it M is the way to go with flash...
 
A
Tom Pinchenzo said:
Hi all, thanks for your thoughts. It's not straightforward, is it, no matter how it's explained! I think I just need to play around. By the sound of it M is the way to go with flash...
Click to expand...
Well actually yes it is as Long as you think of it as two exposures one for ambient and one for flash.
Next yes Id recomend using M on camera since the exposures compensation tend to affect both ambient and flash and lastly use flash exposure compensation if TTL is a must
 
Tom Pinchenzo said:
Hi all, thanks for your thoughts. It's not straightforward, is it, no matter how it's explained! I think I just need to play around. By the sound of it M is the way to go with flash...
Click to expand...

The real answer is that you need to test, test and test again until you know how it works and then it does not matter if you are on A, S, P, M, and spot, partial or matrix metering etc. etc.

Mike
 
and M needs care to manually set ISO and not leave in auto ISO. In auto ISO with flash, the camera needs to choose an ISO and it may not choose the one you want.
 
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