Metering with a flash

[Benbo]

I've recently bought a SB600 to use with my D80 and one thing that confuses me is how does metering work with a flash unit?

Usually in manual mode (without a flash) you can fiddle about (technical term) with the aperature/shutter speed until the indicator shows a correct exposure (using spot metering). But if a flash is on the camera, does this meter have any relevance?

I'm presuming that the light from the flash is so rapid that the shutterspeed has little effect on the lighting of the subject, controlling only the amount of ambient light that will reach the sensor.

so I guess my question is, how do you meter using a flash in manual mode? What does the flash do automatically and what needs to be configured? Do I just take a picture using a set Fstop and shutter speed and then adjust flash output to get the right exposure (and then fiddle about with shutter speed/aperature depending on the effect I'm after)?

Any pointers to help a flash newbie would be hugely appreciated.

 

[subseasniper]

When using flash I try to think of an image as two different exposures, the part lit by flash and the part lit by ambient light.

Your right that shutter speed has no effect on flash, only by changing the aperture can you alter the brightness of flash (unless of course you alter the output of the flash or move its position).

What to do is set your camera to manual and set and exposure for the ambient light. It is recommended you underexpose by a stop or two.

Then switch on the flash and leave it on TTL mtering. When you take your shot the flash will light the foreground subject and the settings previously dialled in will take care of the ambient light level.

 

[Benbo]

Golddust answer. Cheers buddy.

 

[Mike V]

I think subseasniper has got a good way of going about it.

When he mentions thinking of two exposures, one for flash and one for ambient lighting, I do a similar thing, I try to work out which shutter speed and slower will start to effect the background. i.e. motion blur etc.

A group of us shot at a church recently, using a portable flash kit. We managed to light the subject but the background was too dark. It was then necessary to use a longer shutter speed to allow the background to be filled in using the natural light. Hence two exposures. Thinking about the slowest I could go to get the background in and yet not get any motion blur in the foreground(subject)