Correct Answer for 3:1 Lighting Ratio - Page 6
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  1. #51


    Clear your mind and take a deep breath. The difference between the Highlight side and the shadow side would meter at 6.5 stops. In order to create this ratio the power of your lights woul be increased 3 stops. Keep in mind that each time it is increased a stop it doubles the units of light so (2x3=6) plus the overlap of the fill .5 = 6.5. This is why Michael keeps saying not to confuse exposure with ratio.

    Ratios are not merely something we observe. We can create them. that is the whole point behind the math. To be able to predict and manipulate results.

    There are a many reasons your tests may be yeilding different results. Distance of lights to subject, setting of power going to each light, bounce off walls acting like reflectors, use of any automated self adjusting devices on the lights. All of these things could be throwing your results off. Thats why they invented math. Trust the rules not your eyes. Keep running tests and making adjustments until you get the target.

    Your rule of thumb was a stroke of genius and it works beautifully. Using your rule and Kirk's diagram I worked my way backward through the math. To get to know the rule forward and backwards.

    As you can see we are all learning and re-learning on this thread, don't give up!
    Last edited by David_A._Lottes; 09-18-2006 at 02:59 PM.

  2. #52

    Default Lets re-open this can-o-worms!

    Hello all!
    I can't wait to see if someone cleared this up in the down time! I have been re-working the numbers and still can't figure out where we're going wrong, or if we are! Let's work this one out! And if we do lets have another question from the sample test. This is a GREAAAT thread!

  3. #53
    Join Date
    Jan 2006
    Centennial, Colorado


    I was always taught that 3:1 was a 1.5 stop difference. For example, Art Ketchum (, the guy who taught me lighting ratios, taught me the "perfect" setup is key @ f8 fill @f4.5, Kicker/rim light/s @f5.6 and hair either f11 or f16 adjustable by color of models hair.

  4. #54
    Join Date
    Aug 2005
    Petaluma, CA


    Jay, the 1.5 stops is an exposure difference, not a difference between the main and the fill. The main and the fill are a 1 stop difference.Michael
    Michael Gan,M.Photog.Cr. CPP,
    Meritage House of Photography

    If your business depends on you, you don't own a business-you have a job. And it's the worst job in the world because you're working for a lunatic... You can't close it when you want to, because if it's closed you don't get paid. You can't leave it when you want to, because if you leave there's nobody there to do the work. You can't sell it when you want to, because who wants to buy a job?
    —Michael Gerber

  5. #55
    Join Date
    Aug 2005


    When you are working with this ratio issue you need to know that there are 2 different ratios discussed.

    1 - Lighting Ratio: The ratio of light quantity falling onto the subject.

    2 - Light Ratio: The ratio of light quantity from the light source.

    Lighting Ratio is better thought of as contrast ratio. Thinking in these terms you think of the contrast between the high-light and shadow side of your subject's face (for a portrait).

    Light Ratio is thought of in terms of how much light output each light is providing. It doesn't take the subject (or what the light is falling on) into consideration.

    Be very careful when you read the question to determine exactly what they are asking as the answer will be different in each case.

    A lighting ratio (contrast ratio) of 1 stop will produce a 3:1 ratio.

    Fill light at f8 has a light output of 1 unit. Main light at f11 has a light output (relative to fill) of 2 units (1 stop more light). The fill provides 1 unit of light on the shadow side of the face and 1 unit of light on the highlight side of the face. The main provides 2 units of light on the highlight side and 0 units on the shadow side. 2+1=3, 1+0=1. 3:1

    A light ratio of 1 stop will produce a 2:1 ratio.

    The fill at f8 provides 1 unit of light. The main at f11 provides 2 units of light (relative to the fill). What the light is falling onto is irrevelent. Therefore a 2:1 ratio.
    Last edited by Don_Chick; 09-21-2006 at 01:21 AM. Reason: clarity
    M.Photog., Cr., CPP, D.C.Ph.

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