Correct Answer for 3:1 Lighting Ratio - Page 4
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  1. #31
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    Default

    Okay. I realllyyyyyy appreciate all the input on this. I know how I will answer the question on the test depending on how it is worded, I think

    Deb

  2. #32
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    Default Solved, then.

    Quote Originally Posted by Karen Linsley
    I beleive Deb is referring to this question, from the sample test on this web site: http://certifiedphotographer.com/fil...ampleItems.pdf

    8. In a portrait illuminated with a 3:1 lighting ratio, comparisons of the highlight side of the face with the shadow side would produce a difference of how many stops? a. 0.5; b. 1.5, c. 2.5; d. 3.5.

    Correct answer according to the test sample is ...........B. 1.5 stops.
    Hah! Yes! Look at my diagram and my explanation above. The shadow side is being illuminated by 100 watt seconds, the highlight side is being illuminated by 100 ws + 200 ws, which is triple the amount of illumination.

    If it were 100+100 (doubled) it would be one stop more. It would need to be 100+100+100+100 (quadrupled) to be two stops more. It's only tripled, which is 1.5 stops more.

    There it is.
    --Elephants can swim...
    ...and very gracefully.
    Knowing that,
    I do believe
    Anything is possible for me.

    Kirk Darling, CPP

  3. #33

    Default

    Yes Kirk
    Your Diagram was spot on.......but you also said....... "You get a 1.5 stop difference if you meter incorrectly"..........not what I would call nailing it.

    Let's face it none of us gave a clean answer here even though we all knew how to accomplish the task. That's a shame.

    I blame the loosey goosey manner we've been encouraged to imulate. Even if our image making skills aren't rusty our communiction skills are.

    But you sure came closer than me..........I'M NOT WORTHY, I'M NOT WORTHY, I'M NOT WORTHY (spoken while genuflecting).

    Respectfully - David

  4. #34
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    OK,
    I was very confused about all of this until I heard David Ziser explain it. It's basically just like Kirk's diagram but he broke it down like this...

    Pretend your main light is F11 and your fill is F8. F8 is assigned 1, since it is the weaker of the lights. F11 is assigned 2 cause as we all know F11 is 2X as powerful as F8. So, you have 2 "units of light" (for lack of a better term) hitting the highlight side of your subject and 1 unit filling in the shadows, BUT light is additive SO the one unit filling in the shadows is also hitting the highlight side as well. So 2+1=3 "units of light" on the highlight side and 1 unit of light on the shadow side. 3:1... at least that's how I understand it.
    Dan Leary, CPP

    When you find yourself on the side of the majority, it is time to stop and reconsider - Mark Twain

    www.learyweddings.com
    www.dmaxphotography.com

  5. #35
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    Quote Originally Posted by David A. Lottes
    Yes Kirk
    Your Diagram was spot on.......but you also said....... "You get a 1.5 stop difference if you meter incorrectly"..........not what I would call nailing it.
    I was confused by the link. I had it right in my explanation above the diagram, but metering the two lights individually didn't come to 1.5 stops difference unless it was being done incorrectly.
    --Elephants can swim...
    ...and very gracefully.
    Knowing that,
    I do believe
    Anything is possible for me.

    Kirk Darling, CPP

  6. #36

    Default

    Hello all, I thought I'd chime in on this topic. I think I may have a simple way to understand ratios.

    The question that was asked in the original post had to do with the CPP exam. The CPP exam question gave us the difference in f/stops between the shadow and highlight (in this case it was 1.5 stops) and asked what the lighting ratio was given this information.

    Each time we open up or close down one f/stop we are either allowing 2 times as much light to enter through the lens or reducing that amount by 1/2. So everything we do regarding ratios is either multiplied or divided by 2. If we know that there is a 1.5 stop difference we multiple 1.5 x 2 which equals 3, hence a 3:1 ratio. This works every time as long as we know what the f/stop difference is between the highlight and shadow.

    If the question had given us a ratio, for instance 7:1 and asked how many stops difference there is between highlight and shadow, we would divide 7 by 2 which equals 3.5. So the answer is 3.5 stops.

    How each photographer meters to obtain the difference between highlight and shadow can be up for discussion. I've seen it done several different ways. And each way might yield different results. But once you decide on a value between highlight and shadow, simply multiplying by two will yield the correct ratio for that value.

    I hope this helps anyone struggling to understand this topic.


    Joseph Froeschle

  7. #37
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    Quote Originally Posted by Joseph Froeschle
    Each time we open up or close down one f/stop we are either allowing 2 times as much light to enter through the lens or reducing that amount by 1/2. So everything we do regarding ratios is either multiplied or divided by 2. If we know that there is a 1.5 stop difference we multiple 1.5 x 2 which equals 3, hence a 3:1 ratio. This works every time as long as we know what the f/stop difference is between the highlight and shadow.

    If the question had given us a ratio, for instance 7:1 and asked how many stops difference there is between highlight and shadow, we would divide 7 by 2 which equals 3.5. So the answer is 3.5 stops.Joseph Froeschle
    Okay, yeah, woooo hooo, I get it! I just needed that last boost to put me over the edge to understanding.

    Thanks Joseph!

    Deb

  8. #38

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    QUESTION: In a portrait illuminated with a 3:1 lighting ratio, comparisons of the highlight side of the face with the shadow side would produce a difference of how many stops?

    Answer:
    Quote Originally Posted by Joseph Froeschle
    1.5 x 2 equals 3, hence a 3:1 ratio.
    NOW THAT WAS CLEAN!

    You Rock Joseph!

  9. #39

    Default Let's see what we've learned

    Knowing those sneaky testers they will phrase the question differently on the actual exam. So let's see some different questions. We could do this like the "Name That" thread. I'll ask a ratio question and whoever gets it right can ask the next one. But wait for confirmation from the person who asked the question. Here goes.

    A portrait with a 5:1 ratio, comparisons of the Main light to the Fill light can be created with which combination?

    F8.5 (Main) and F5.6 (Fill)

    F11 (Main) and F5.6 (Fill)

    F11.5 (Main) and F4 (Fill)

  10. #40
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    So everything we do regarding ratios is either multiplied or divided by 2. If we know that there is a 1.5 stop difference we multiple 1.5 x 2 which equals 3, hence a 3:1 ratio. This works every time as long as we know what the f/stop difference is between the highlight and shadow.

    Wow, Joseph, thanks. Great thumbrule. Everybody who is going to take the test, be sure to memorize this. I'm not kidding.
    --Elephants can swim...
    ...and very gracefully.
    Knowing that,
    I do believe
    Anything is possible for me.

    Kirk Darling, CPP

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