Before we even begin deliberating how to work with manual flashes, let’s just find the answer to the why part. Why would somebody want to work with manual flashes? For, they’re cheaper. But they’re also not as difficult to use as you might think. Daniel Norton from Adorama demonstrates in this video:
If you have any old flashes from the bygone film era lying around in your studio, you might not know what to do with them. These flashes don’t work with digital cameras the same way they did with film cameras.
Manual Flash Guide Numbers
Most photographers opt for the trial and error method when shooting with these flashes, starting with an educated guess and taking it from there. Norton has a better idea: using the guide number of the flash.
“You basically divide the guide number by the distance and that’s your aperture.”
By reverse calculating the guide number you get the right aperture to shoot with. In the below example the flash is at a distance of 10 feet away. The guide number is 112 at 10 feet. That means the right aperture to shoot with is f/11 (with the flash zoomed all the way to 105mm and at full power). It produces a good exposure as you can see:
Using Manual Flash with an Umbrella
What if you are using an umbrella? Out of experience Norton knows that an umbrella eats up about two stops of light. He corrects it later to just one stop because of the silver reflector inside the umbrella (which reflects more light). So, this is the result at f/8:
As you can see the exposure is probably OK. But to further test out the theory Norton uses a grey card, which gives a better assessment of the exposure. The test image reveals he’s about one-third stop underexposed. Norton corrects the aperture by one-third stop to f/7.1 to produce this image.
Check out the rest of the video to find out how to test the correctness of an exposure using a digital target as well as how to use a second manual flash and set it up as a hair light.
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