Last weekend, thanks to a birthday present from my wife, I got to spend a good number of hours with full time professional photographer Mark Weeks.  We reviewed my top images, talked about photography in general, the limited sensor range of a dSLR, equipment and lighting, exchanging a few tips and tricks along the way.  For me the most valuable thing, other than to get some cinefoil was the “eureka” moment when I realised I should be using what I’ll refer to as differential metering using the camera.

Mark has a light meter he takes almost everywhere, used so much the printing on the buttons has gone.  It’s a piece of equipment all photographers with stobes are encouraged to purchase. Having used one in a studio that was reporting values at least a full stop out I was reluctant.  Mark explained that sort of things okay if it’s always your meter you’re using, you just get used to it and compensate.  Having set his F-stop to the required value for the shot he goes about metering any ambient, key, fill or rim light sources,  looking for meter readings above and below his working aperture.

It occurred to me that when using the Expodisc I not only get an indication of the colour of the light but its exposure.  Shooting in P mode, the camera changes the aperture and shutter speeds to get a good exposure resulting in the spike in the middle of the histogram.

What if I nailed one or both of these down? As expected, setting Av mode and the aperture I want to work at (Fn) gives the same shutter speed P would have used. Taking that shutter speed and using it in M mode with Fn we then get the spike in the same place. For metering the ambient light it’s as easy as turning the shutter speed and f-stop dials until the meter is in the middle of the gauge, or a fraction below if we want the ambient light to take a more minor part in the shot.  In use the Expodisc is always pointed at the light source, not the subject.  The “eureka” moment came from realising how the camera would show spikes for any photos of the flash or flash-reflector sources.  By thinking just about the differences between them all I get the same results for a faction of the price of a digital flash meter.  In the image above it’s clear that the rim light I’d photographed is a full stop over, just where I want it.

And an Expodisc doesn’t need batteries and can easily be stored in any already full kit bag.  If you use this technique ensure you photograph the lights from the subject location, not closer or further away as you’ll impact the results by approx 1 stop per meter.