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Thread: How much Flash Power ?

  1. #1

    Default How much Flash Power ?

    I am new to shooting flash with umbrella. As i dont have digital camera or flash meter, I have to learn flash power by heart. I am using SB-28 at iso 100, 1/125, 45 degree on a stand to the left of camera, 45' inch umbrella, maximum shaft length. no fill on the opposite side of subject face. Below are my findings :-

    [A] shoot thru umbrella

    flash to subject distance flash focal length flash aperture flash power
    1.5m 24mm F2.8 FULL
    1.5m 85mm F4 FULL

    [B] reflect from umbrella

    flash to subject distance flash focal length flash aperture flash power
    1.5m 85mm F2 FULL

    Please comment whether these settings are similar to yours.
    Last edited by CasualSnaper; 6th March 2008 at 11:33 PM.

  2. #2
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    Default Re: How much Flash Power ?

    well, in current age and time, dun think it will be appreciated. but still nevertheless, nice research.

    btw, iso matters as well, and light angle and amount of fill.
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  3. #3

    Default Re: How much Flash Power ?

    Not that it's not appreciated, but I don't think that anyone would even know or remember the data, assuming they are using the same exact flash, umbrella, flash-to brolly distance and brolly reflectance/translucency factors.

    However, I suspect you might be able to actually calculate a range of useable settings working on your base findings. I used to do entire tables with my darkroom formulation based on sets of base variants and test results - very tedious and time consuming, but it was really fun and helpful when I got it right.

    Most togs I know don't even use a flashmeter - they prefer to whack and check on their LCD screens because they are shooting digital.
    Last edited by Dream Merchant; 7th March 2008 at 09:57 AM.

  4. #4
    Moderator catchlights's Avatar
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    Default Re: How much Flash Power ?

    Your setting for this is incorrect.

    to get consist results, you need to FIX the flash zoom angle (should be at 35mm), and ONLY use the Manual flash power output setting, eg 1/1 power , 1/2 power to 1/128 power.

    you need to understand the "inverse square rule" for doing flash set up.
    You can attach a string on the umbrella (the light source), when the flash is 1/1 power, let say the distant of the umbrella to your subject is 5ft, and it gives you the exposure is at f8, make a f8 marking on the string 5' position.

    now, if the subject is 10ft away from the umbrella, you get f4, (you can mark a f4 at the string at 10ft length)
    2.5ft away from the umbrella, you get f11, (do a marking likewise)

    if without changing the distant between umbrella and your subject, you can power down the flash to change the output, eg, if 1/1 power is f8, 1/2 power will be f5.6, 1/4 power will be f4, so on and so fore.
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  5. #5

    Default Re: How much Flash Power ?

    VERY GOOD ADVICE. your method is fast and useful. THANK YOU.

    I shot these at 1.5m 85mm F4 FULL throughout the whole shoot.
    http://www.clubsnap.com/forums/showthread.php?t=359816

    i go for group shoot. if i could get closer to the model for example 1m away. I will get 85mm F5.6 FULL.

    After the above shoot, i think i could get 1 more F-stop. i.e. 1.5m 85mm F5.6 FULL or 1m 85mm F8 FULL with my setup.

    I tried 85mm because i had underexposure before and because i thought SB-28 is not powerful enough.

    I will try wider flash focal length to see whether the light quantity will be less harsh.

    I know flash at F1.4 is very "flare". I want to try Flash and camera at F8 to make photo sharper.

    It seem like your flash is more powerful.
    5ft 35mm F8 FULL vs 1m 85mm F8 FULL

    Is there any difference in light quality for the following settings:-
    F8 FULL and F5.6 1/2

    Quote Originally Posted by catchlights View Post
    Your setting for this is incorrect.

    to get consist results, you need to FIX the flash zoom angle (should be at 35mm), and ONLY use the Manual flash power output setting, eg 1/1 power , 1/2 power to 1/128 power.

    you need to understand the "inverse square rule" for doing flash set up.
    You can attach a string on the umbrella (the light source), when the flash is 1/1 power, let say the distant of the umbrella to your subject is 5ft, and it gives you the exposure is at f8, make a f8 marking on the string 5' position.

    now, if the subject is 10ft away from the umbrella, you get f4, (you can mark a f4 at the string at 10ft length)
    2.5ft away from the umbrella, you get f11, (do a marking likewise)

    if without changing the distant between umbrella and your subject, you can power down the flash to change the output, eg, if 1/1 power is f8, 1/2 power will be f5.6, 1/4 power will be f4, so on and so fore.

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