One thing I still don't get with fill flash

[HoppyUK]

Thanks. It does seem that you're confirming what I already thought with regards to manual exposure, in that you set it such that the ambient light contributes to the scene but the flash still has to contribute the rest or majority of the light.

What I still can't wrap my head around is how Av/fill-flash mode works at all as using this mode will set the exposure for ambient light only, producing a very slow shutter speed. The flash can't adjust its output to cope with this situation as the exposure assumed no flash at all so any light it produces would be "too much".

Your third paragraph would seem to suggest you've experienced this very effect which just adds to my bemusement about how fill-flash ever works indoors.

If I understand correctly what you're driving at, you're applying a theory. In practise, it doesn't work like that (although the theory is sound).

If the ambient exposure is correct, then why are you bothering with flash anyway? The reason is usually that the ambient light isn't suitable in quality, not just overall quantity. It will put nice light where the ambient is not giving you much, so there is no potential for over-exposure there. And in the areas where there is sufficient ambient exposure, the maximum potential over-exposure is one stop.

In practise, this usually isn't much of a problem but it is common practise to moderate both the flash/ambient balance as well as the overall exposure level. Check the LCD, enable blinkies, check histogram, make changes as necessary - this kind of thing varies quite a bit depending on the situation.

My preferred mode for doing this is Av, which allows me to use +/- compensation on the camera to adjust the background exposure (by changing shutter speed) and +/- compensation on the gun to control flash exposure (changing output power).

 

[Vertigo1]

If I understand correctly what you're driving at, you're applying a theory. In practise, it doesn't work like that (although the theory is sound).

Yeah this

I'm not saying it doesn't actually work in practice, I'm just trying to wrap my head around how it works at all as it seems to defy logic

I just like to understand how things work.

 

[Lensflare]

Vertigo - it works on a scale set in the camera electronics - just like the program mode will use a pair of settings on the sliding scale for the ISO you choose according to the light meter measurement.
So, the shutter speed may be slow - that is because of the ambient being low. The flash pop is just a tiny flick of light in those cicumstances. The same amount of ambient in flash lighting settings would up the shutter speed, thus blocking much of the ambient, but the flash hit is going to be much the same. You are getting slow shutter speeds because yu have it set to slow synch. If you change your flash shutter speed settingn you can (with Nikon) choose from 1/250 right down to, I think, 1/15 (might be 1/30) - normally a flash synch setting (on 100) will stick the shutter on 1/60 and have done. It will depend on your ISO setting too don't forget. I do, because I have gone through life having to use 50 - 200 for 90% of my work and only resort to 400 if it was a dire emergency (like mid December, raining and 3pm!) Now, we can use 3200 ISO and it is as good as 400 was in the old days of E6 film (might even be a bit better!)