Q&A: What Are Lighting Ratios

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LR.stevie1Question: In your review of the Multiblitz backpack kit you indicate  some the photographs have a 3 to 1 lighting ratio and have an exposure of 1/125 sec at F/11.  I have a familiarity with lighting ratios but I 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 (filling the shadow areas) 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 f-stop is equal to double the amount of light or two to the power of the difference in f stops.

LR.stevie2For example: A difference in two f-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 0, 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.

Author: Joe Farace

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