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Thread: Does light stack?

  1. #1

    Default Does light stack?

    Ok there's something that I need to clarify 'cause I've been confused about this for a long time.

    Does light stack? To illustrate my question, if I were to have a subject lit by strong sunlight from the right and I were to fire a flash straight on(exposing correctly in M mode for the sun-lit side, metering for flash on the unlit side, perhaps dialling in FEC of -2/3 stop), would this result in the light output from the flash adding to the light output from the sun and really blowing the right side of the subject or would I get a nice fill that's 2/3 stops under? So far I've only tried fill flash with backlighting and I cannot predict how it will turn out because I haven't grasped the above concept. Does light work like sound at all?

    What is necessary to take note of when shooting with combined lighting?
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  2. #2
    vince123123
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    Default Re: Does light stack?

    The answer is yes, light will "stack", although this is the first time I'm hearing the term "stack" being used, but the idea is the same - easy to understand though.

    In your case, the right side will be blown. Not sure if it works like "sound", but it will stack.

    As another example, if you shoot in total darkness, and then put your camera to B model, firing your flash twice will result in twice the amount of flash - this is a technique used by experienced flash users to light up subjects which require more flash power than they have. Sometimes, we use TWO flash units at the same spot to achieve this effet too.

  3. #3

    Default Re: Does light stack?

    It's not the light that "stacks". It's the film which records the increased light.



    Quote Originally Posted by Stoned
    Ok there's something that I need to clarify 'cause I've been confused about this for a long time.

    Does light stack? To illustrate my question, if I were to have a subject lit by strong sunlight from the right and I were to fire a flash straight on(exposing correctly in M mode for the sun-lit side, metering for flash on the unlit side, perhaps dialling in FEC of -2/3 stop), would this result in the light output from the flash adding to the light output from the sun and really blowing the right side of the subject or would I get a nice fill that's 2/3 stops under? So far I've only tried fill flash with backlighting and I cannot predict how it will turn out because I haven't grasped the above concept. Does light work like sound at all?

    What is necessary to take note of when shooting with combined lighting?

  4. #4
    Moderator ortega's Avatar
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    Default Re: Does light stack?

    simple experiment
    take a strong torch light and shine
    is it brighter?

    Change to spot meter and meter with and without "stacking"
    ta da, the answer is yes it will get brighter
    and the additional light can also be used to fill in the shadows

  5. #5

    Default Re: Does light stack?

    Thanks all for your response.
    I used stack because I'm unaware of the proper term.

    So what's the appropriate way to go about using fill flash for the above situation? If I want to achieve a well exposed right side of the face and a left side of the face that is 2/3 stop underexposed.
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  6. #6
    Moderator ortega's Avatar
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    Default Re: Does light stack?

    Quote Originally Posted by Stoned
    Thanks all for your response.
    I used stack because I'm unaware of the proper term.

    So what's the appropriate way to go about using fill flash for the above situation? If I want to achieve a well exposed right side of the face and a left side of the face that is 2/3 stop underexposed.
    get a nikon

  7. #7

    Default Re: Does light stack?

    Quote Originally Posted by ortega
    get a nikon
    Sounds like a case of blaming the equipment, which i really don't want to do.
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  8. #8
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    Default Re: Does light stack?

    In a way yes, since light is a form of energy. More photons to existing photons falling on a subject means more energy to the subject.
    Last edited by Prismatic; 25th January 2006 at 12:36 PM.

  9. #9
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    Default Re: Does light stack?

    what i mean is that the flash systems are intelligent enough to calculate and adjust everything for you.

    if not then meter the flash output and the ambient light and adjust accordingly.

  10. #10

    Default Re: Does light stack?

    Hmm so an external spot meter would be a good idea then. Thanks all for your input.
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  11. #11

    Default Re: Does light stack?

    You really need to understand things better.

    a. Nikon has the best flash system around for 35 mm

    b. It's not about blaming the equipment, more about having the equipment do the job for you. Sure, you can learn to use flash meters and calculate guide nos all by hand if you want, but why go thru all that trouble unless you have no choice.

    On the other hand, if you want a machine to do it for you, some machines are far easier to use than others. That's why the recommendation is to use a Nikon. Their system is so intelligent that you get properly exposed shots every time.

    Quote Originally Posted by Stoned
    Sounds like a case of blaming the equipment, which i really don't want to do.

  12. #12

    Default Re: Does light stack?

    I'm quite firmly stuck in the Canon system. It would be a real hassle to change now. Anyhow, what about external strobes? Do these help at all?

    It's good for me to learn how to calculate as well because I hope to move to MF eventually as well and it would certainly not be Nikon. Might as well learn now.
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  13. #13
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    Default Re: Does light stack?

    External strobes are just like normal speedlites, only more powerful and have more option for accessories. Normally for fill in situations, the fill light should be about 2-4 stops lower than the main (sun light). Unfortunately there is no way to measure this w/o a flashmeter, so you have to get one. Of course there's always an option of using manual mode flash and setting the correct 1/n power, which can be hard to estimate at times.
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  14. #14
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    Default Re: Does light stack?

    just curious, have u actually face the situation?

    if using digital,
    why not experiment?

    just shoot and not happy,
    just try other settings.
    FEL on ur cam is quite clever one u know?
    u might get what u like by simply shooting it.

    jude

  15. #15

    Default Re: Does light stack?

    Yes I have and I cannot get consistent results. I surmise it's because I have no mastery over my system.

    I think a good solution would probably be the flashmeter splutter suggested
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  16. #16
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    Default Re: Does light stack?

    You might wish to try off-camera flash. If you flash cannot be triggered as a slave, then, just get a trigger attachment which is like $20 or so. It is easy to vary the distance of the flash to subject or even do bouce flash to achieve the kind of soft look.

    In digital, you don't even have to calculate - just estimate and shoot at most 2 test shots and it should be able to get it right.
    I love big car, big house, big lenses, but small apertures.

  17. #17

    Default Re: Does light stack?

    I tried some mixed lighting today. It seems that adding -2 to -3 stops to FEC works out quite well.
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