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Using a flash meter to determine (manual) flash power to light an underexposed subject

jcalex3642jcalex3642 Member
edited January 2014 in home
Neil’s Tangent tutorial written on February 9, 2010 entitled “balancing flash and ambient exposue – where do I even start?” takes us through a scenario where the dark-toned model is purposefully underexposed in front of a well-lit background ( Time Square lights in the early evening?). Settings before the model is lit by flash: 1/125 @ f3.5 @ 800 ISO for the background eposure. Neil then lights the model with flash TTL to match the aforementioned settings. All of this I completely understand.

I’m confused about the following statement: “ If I had shot with manual flash, then I would’ve used a flash meter to set my flash output to match my choice of aperture and ISO, for the particular distance I have my light set up. “

My question is: How exactly would you have used the flash meter (with the strobe in manual mode) to arrive at the correct settings to illuminate the model properly without changing your in-camera settings? Values entered into the flash meter? Changing the distance of the strobe to the model during flash adjustment? This would seem to be a tedious process (vs the TTL approach) in this case. Please help me understand this process.


  • In that scenario with background exposed at 1/125 @ f3.5 @ ISO 800 you set your flash meter to f3.5 @ISO 800 and adjust your off camera flash power to get to f3.5. Lets say the first test gives you a meter reading of f4.5. Thats 1 stop over exposed. If your flash was at 1/2 power lower it to 1/4 and you should be good to go. You can also move the off camera flash closer or farther away. You should be able to get the exposure you want in 2 or 3 test fires. TTL varies also. You may luck out if what your shooting is pretty neutral but if you have a lot of white or black in your image you will have to adjust your exposure compensation depending on your subject.
  • Thanks,bob -your explanation is very clear. I appreciate the fast response.
  • Hi bob , im new here and im learning stacks , for the above comment and to clear my grey area i have. If in manual mode to expsose the subject correctly , would u generaly choose to adjust aperture rather than move the light or lower the light out put.
    In some cases i have read that ( dont forget if u raise your flash out put , then u must also adjust your aperture accordingly. ) this sounds contradicting , Bob would this be one or the other or both. Would u care to give a brief example please.
    Jcalex 3642. Thank you for rasing your point. Ive learnt from it as well.
    Thanks bob
  • Stephen:

    In Bobh’s example, you do not want to change the aperture on the camera as that will affect both the foreground and background exposures. By adjusting the flash power or the flash distance you will only affect the foreground exposure.
  • Thanks qrckman. Kinda clears that grey point up.
    Ps i banned my self from using my camera untill i full understand all my variables and exsposure. Becouse i am just wasting my time other wise. ,
    Im almost there now in retaining the info to restart my togging ,, both of neils books are coming tomorrow. ,
  • Stephen in the original scenario we had 1/125 @ f3.5 @ ISO 800 and flash set to 1/4 power for proper exposure. If you change the flash power back to 1/2 power we would have to adjust our aperture to f4.5 for proper exposure on the subject. If we do that then our background will be under exposed by one stop from where we started. Like qrickman wrote adjusting the aperature and flash power will effect both background and foreground of your image.

    Dont be afraid to use your camera! Put your flash on your camera or off camera and set everything to manual. Put someone or something in front of your camera and try different exposures and flash power settings. You dont need a flash meter. Use your histogram and camera LCD to determine proper exposure.
  • Phewwww. Thats makes sense bob. So basicaly once the proper aperture has been found adjust flash power accordingly ie up or down on setting or moving the flash. .
    Bob i did nt wana digress from this subject. The only reason y i put my camera to rest becouse i thought i knew my varialbes ie. , aperture ,iso and shutter speed and i did nt well not fully. And wasted 2.5 years grabbing good composition and thats it and chasing natural light. I have a handfull of shots that i consider good. And thats a bad result.
    Niel mensioned in a podcast , about a lazy artist who could nt be botherd to learn the tech side of things. And he also mentioned consistency. I was both of them. ( purly for the fact i was to nackerd thhrough my current job as a heating engineer working late etc )
    For eight weeks now i have studied read book and you tube for hours and the penny has dropped. Ive retained the info and so i feel wont be wasting my time going for a shoot . I now fully understand the relationship with all three variables
    The camera will be coming back out.
    Basicaly bob ive gone back to the start again and im am massivaly hooked.
    Ps im waiting for me books from amazon. Off camera flash and direction of light. So cant wait
    Wat i love here also is guys like your self and neil that gives out support and encouragement.
    This is not a pompos site and so love it
    Thanks again
  • Neil vNNeil vN Administrator
    jcalex3642 said: My question is: How exactly would you have used the flash meter (with the strobe in manual mode) to arrive at the correct settings to illuminate the model properly without changing your in-camera settings? Values entered into the flash meter?
    It is much easier than you think.
    And here's an article to explain it all, just for you. (and the rest of the world)
  • Neil,

    I get it...finally. You've explained it in such simple layman's terms.

    How do you balance the flash/ambient in the same situation without a flash meter using manual flash?

    Can it be done?


  • Neil vNNeil vN Administrator
    By eye, looking at the LCD?
  • Neil is right. The LCD is your friend. It is there as part of the tools to achieve your results. Don't let people scare you into not using it to make sure you are getting what you want. It would be like saying I am going to read the newspaper and never watch tv news!
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