Flash photography: 1:1 rule-of-thumb

As I was setting up for my first foray into tethered macro studio photography, I was reminded of the 1:1 rule-of-thumb that is used to determine how close/far to position a flash unit from the subject.

The diagonal distance across the face of a softbox should be the distance to the subject [or less] for soft wrap-around light. Actually, the distance should be as close as possible without the softbox showing in the photo frame. Greater distances will result in a contrasty look.

For example, my Altura softbox is a 6” x 5” rectangle (~7.8” diagonally) so it should be positioned ~8″ or less from the subject. Buyer beware: This distance is OK for macro photography but not OK for most other types of photography.

Product image courtesy altura PHOTO.

My Lastolite Ezybox Speed-Lite 2 is 8.6″ square (~12.2″ diagonally) so the softbox should be positioned approximately 12″ or less from the subject.

Product image courtesy B&H Photo.

Online Calculators

For small softboxes like the ones shown above, the diagonal distance can be measured with a 12″ (~30 cm) ruler. For larger softboxes, it might be easier to use an online calculator to determine the distance.

Application

How far should should an external flash unit fitted with some type of diffuser be positioned from the backside of a translucent white plastic sheet used to create a pure white background (255, 255, 255) using the “Meet Your Neighbours” (MYN) technique?

As it turns out that’s a little more complicated to calculate, assuming you would rather not waste time with trial and error experimentation. Stay tuned for a follow-up post in which I will explain how I figured it out.

Related Resource: Flash photography: Backlighting the background.

Copyright © 2020 Walter Sanford. All rights reserved.

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2 Responses to “Flash photography: 1:1 rule-of-thumb”

  1. Mike Powell Says:

    So far I can follow the math easily enough, Walter, but if it gets too advanced, I may have to simply trust you. “)

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