Q&A: What Are Lighting Ratios

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Question: In your review of the Multiblitz backpack kit you indicate that some the photographs have a 3 to 1 lighting ratio and have an exposure of 1/125 sec at f/11.  I’m familiar with lighting ratios but am weak in some aspects to the setup and execution of them. Would I be correct in believing the main light is set to f/11 and the background light is set to f/4 which gives the 3 to 1 ratio or did I miss something here?  It seems as if the more learn the more I realize there is much I have to learn.

Answer: Lighting ratio refers to a comparison of the key—or main—light to the fill light. The higher the lighting ratio is, the higher the contrast of the image will be and conversely; the lower the ratio, the lower the contrast. A ratio can be determined because each increase in aperture is equal to double the amount of light or two to the power of the difference in f stops.

For example: A difference in two stops between the key and fill lights is 2 squared or a 4:1 ratio. A difference in three stops between the light is 2 cubed, or an 8:1 lighting ratio. If there is no difference at all between key and fill the lighting ratio is equal to two to the power of zero, which produces a 1:1 ratio.

For the 3:1 lighting ratio used in my shots for the Multiblitz review, there is a one-stop difference. A lighting ratio of 3:1 is considered normal for color photography but photographers can be flexible in applying this rule and to tell the truth I seldom worry about hitting a specific ratio. The image at left was shot with a Canon EOS 5D Mark I with EF 28-135mm f/3.5-5.6 IS USM lens (at 80mm) with an exposure of 1.125 sec at f.11 and ISO 100.

Screen Shot 2016-03-26 at 9.13.43 AMIf you’re interested in shooting portraits and how I use cameras, lenses and lighting in my in-home studio, please pick up a copy of Studio Lighting Anywhere” which is available from Amazon.com with used copies (as I write this) selling for less than $4—the best deal you’ll find. New copies are $17.50, so take your choice.

Author: Joe Farace

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