It’s a question that’s often seen in photography groups. For some reason, people want to know all of the technical specs and exposure settings of every photo posted to those groups. In flash groups, people even want to know what flash power level you were at – as if it was actually a useful question to know the answer to.
Photographer Rob Hall sees this question all the time, so he’s decided to respond with a video. But this isn’t just a rant about why it’s a dumb question – well, not completely. Rob also tries to inject some knowledge to explain why the answer to the question is irrelevant and suggests some questions that you should be asking instead.
The reasons why people ask for the flash power do seem innocent and useful enough at first glance. They want to know what kind of conditions they can shoot in with a given light to aid their own buying decisions. But here’s the thing, the same light won’t always work in the same weather conditions. The modifier being used (and the size of that modifier), as well as the distance between the flash and the subject, all have a huge impact on how much light it can put out.
You can make a speedlight overpower the sun if you’re close enough or you could have a 600Ws strobe that can’t give you enough light even on a cloudy day – especially if you’ve got the light way back in a big modifier to photograph a group and you need the kind of depth of field that only f/8 can provide. Just knowing the brightness output of a light for a given shot doesn’t really tell you much at all, really.
You’ve also got inconsistencies between cameras and lenses themselves. There are 9/10ths of a stop of difference between my darkest and brightest cameras at the same ISO, aperture and shutter speed settings, even with the same lens. That means on my darkest camera, your light would need to be twice as powerful as on my lightest camera. That’s why handheld light meters (like those from Sekonic) need to be calibrated to your camera when shooting digital.
I won’t spoil all of Rob’s video for you here, just go watch it. Listening to somebody explain why the information is largely useless will give you a better understanding of what is important when choosing which lights you should buy and how to use them in your photography. And pay particular attention to the questions he suggests you should be asking instead.