Wattseconds - Huge difference?

Discussion in 'Photography' started by Melody, Sep 8, 2005.

  1. Melody

    Melody Guest

    When shooting digital is there a noticeable difference between 400Ws & 800Ws
    (effective) lighting?

    Thanks :)
     
    Melody, Sep 8, 2005
    #1
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  2. Melody

    Colin D Guest

    Digital has nothing to do with it. 800Ws is twice the ilumination of
    400Ws, so it's one stop difference.

    A flash rated at 800 Ws gives the same total light as if an 800-watt
    lamp of the same luminous efficiency was on for one second, or, if the
    flash duration was, say, 1/1000 sec, then equivalent to an 800,000-watt
    lamp for 1/000 second. It's all linear.

    Colin D.
     
    Colin D, Sep 8, 2005
    #2
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  3. One stop.
     
    Randall Ainsworth, Sep 8, 2005
    #3
  4. Melody

    Melody Guest

    Thanks, I am aware of all that. I'm just constantly told that digital
    photography (which, again, I'm just delving in to after years & years of
    film) isn't as sensitive to light as film (makes sense). So I'm just
    wondering if there's even a noticeable difference in the photographs when
    using 400 vs. 800 Ws lighting. Obviously I'm hesitant to pay the extra money
    if there's no noticeable difference. Thanks again!
     
    Melody, Sep 8, 2005
    #4
  5. Melody

    Bruce Chang Guest

    Digital isn't as sensitive to light as film? I'm not sure how that "makes
    sense." Please explain.
     
    Bruce Chang, Sep 8, 2005
    #5
  6. Melody

    DBLEXPOSURE Guest


    You are right but, I do not think it is "Linear". Logarithmic actually.
    But your point is made..
     
    DBLEXPOSURE, Sep 8, 2005
    #6
  7. Melody

    Mike Kohary Guest

    Yes, there's the same difference as when using film. :)
     
    Mike Kohary, Sep 8, 2005
    #7
  8. Melody

    Mike Kohary Guest

    Why does that make sense? It doesn't make sense to me. If anything,
    modern digital sensors could be said to be MORE sensitive to light,
    because they offer less dynamic range (bad) and less noise at high
    ISOs with a quality sensor (good).
     
    Mike Kohary, Sep 8, 2005
    #8
  9. Melody

    DBLEXPOSURE Guest

    Hmm. I think the stament, "less sensitive to light" is incorrect. Perhaps
    what was really ment was less sensitive to small changes in light, i.e.
    dynamic range. In this case, one stop, would not be considered a small
    change. My understanding is that dynamice range could be said to be the
    ability to render details in shadows or slight changes in light.

    ANyway, doubling the power of the flash is, I agree, one stop. which has no
    bearing on dynamic range.
     
    DBLEXPOSURE, Sep 8, 2005
    #9
  10. Melody

    Colin D Guest

    The *response* of sensitive media to light may be logarithmic, or a
    power function (gamma), but the simple change in light levels from a
    illuminating device, e,g, 400Ws to 800 Ws, is linear.

    Colin D.
     
    Colin D, Sep 8, 2005
    #10
  11. Melody

    Colin D Guest

    No, it doesn't make sense. First, sensitivity - the degree of response
    to light stimulus - is irrelevant with respect to changes in light
    value. A doubling of the light as in your example results in twice the
    exposure of the sensitive medium, i.e. one stop, regardless of the
    medium or its absolute sensitivity.

    Second, stating that digital sensors aren't as sensitive as film is
    patently ridiculous. How do you think digital sensors are able to
    capture images at 3,200 ISO with far better results than film of the
    same speed?

    I think you should cease taking advice from people who give you such
    wrong information.

    So I'm just
    If the studio setup is unchanged then the difference is one stop. One
    stop overexposure is not good for digital cameras, as with
    transparencies. One stop underexposure won't give any problems,
    specially if you are shooting raw.

    If you shift the lights around then exposures will change. But the
    difference is still one stop, however you set them up.

    I think your choice of 400 or 800 WS lamps will depend on what you are
    intending to shoot. Portraits, groups of two or three people, 400 Ws
    will do it. Commercial shoots like cars, or large group shots may
    dictate 800Ws or even more, depending on distance, evenness of lighting,
    depth of field required, etc. Not much good if the light calls for f/4
    when you need f/8 for dof and you're already at 800 ISO.

    Colin D.
     
    Colin D, Sep 9, 2005
    #11
  12. Melody

    DBLEXPOSURE Guest


    Hmmm. I really do not mean to be argumentative. But I am not understanding
    what you are trying to say. If you remove the word watts and replace it
    with the word apples, for instance, then I would agree with you. If you
    count up to 800 from 400 it is linear, But we are not talking about apples
    we are talking about power and it increases on a logarithmic scale. An
    increase from 400W to 800W is one stop as is an increase from 800W to 1600W
    is still one stop, and is also an equal increase in the amount of light.

    Increasing from 400W to 800W to 1200W would be linear but the increase from
    800W to 1200W is only half the increase, (of the amount of light), as the
    increase from 400W to 800W. This doesn't apply only to the response of film
    or digital sensors to light but anything that responds to light. trying to
    apply the numbers to something that does not respond to light, makes no
    sense. Now, if we are going to count photons, then I am not sure about the
    math... If you are talking about foot candles, for instance, 1W=4FC, that
    relationship would be linear. but, remember, foot candles is just another
    way of expressing power, as is lumen or lux or any other derivitive.


    This is why we use, "Stops", so we do not have to think logarithmically.
    Like the aperture, we count up or down one stop at a time but the physical
    area of the opening is changing, logarithmically..


    Now, none of this is taking in the efficiency of the lamp. in a 400W lamp
    some, if not allot, of that energy is given off as heat. There are more and
    less efficient lamps, and I assume there efficiencies do not change in an
    linear way either. i.e. an 800W lamp may be less efficient than a 400W lamp
    of the same filament material, or maybe visa versa??


    Back to the OP...

    I believe the confusion about the phrase less sensitive may have been a
    reference to what another poster has already mentioned, Dynamic Range. Not
    all film is created equal either but I think it is safe to say the best
    films have a better dynamic range than the best CMOS sensors. (I have not
    researched this and there certainly could be a sensor out there to prove
    this wrong). But, this has little to do with lighting and more to do with
    capturing slight changes is the light gradient in a scene. i.e. shadow
    details...

    It would be interesting to know how the pick ups in high end film scanners
    compare with pick ups in high end DSLR cameras regarding dynamic range..

    If you prove my wrong, well it won't be the first time..
     
    DBLEXPOSURE, Sep 9, 2005
    #12
  13. Melody

    Colin D Guest

    Power output, as in any energy-consuming device, is linear with power
    input. Double the power in gives double the output, whether light, heat
    or whatever.
    Of course. Miles are linear. 400 to 800 miles is double the distance.
    800 to 1200 miles is 50% more distance. That is absolutely linear.
    Likewise, increasing the power from 800 to 1200 Ws is an increase of
    50%, and you get 50% more light. That's linear too.

    Actually, stops, i.e. f-numbers, are linearly inversely related to the
    aperture diameter. Doubling the f-number from f/4 to f/8 halves the
    aperture diameter. There is no logarithmic function involved here.
    There is a square root function involved with the progression of
    f-numbers, because the area of an aperture is proportional to the square
    of the aperture diameter. But it isn't a logarithmic function.
    F-numbers are arranged to give double (or half) the light passed with
    each stop change. Because aperture area is proportional to the diameter
    squared, f-numbers have to progress in increments of sqrt(2) to achieve
    the 2:1 ratio between stops.
    It is assumed that as the lamps are of the same type, e.g. flash units,
    the efficiency is for practical purposes the same, so you can discount
    that as a variable.
    This is a hoary old chestnut promulgated by persons either ignorant of,
    or biased against digital sensors. The dynamic range of a sensor is at
    least as good as film, probably better, specially at the shadow end.
    Not relevant here, sorry.

    Colin D.
     
    Colin D, Sep 9, 2005
    #13
  14. Melody

    Bruce Chang Guest

    Stops are logarithmic, yes. Expose more by 1 stop, illumination increases
    by 100%, Expose more by 2 stops, illumination increases by 300%. 3 stops,
    700%

    However, in a linear relationship, as you increase power, you increase
    illumination at a 1 to 1 ratio. You increase power by 100%, illumination
    increases by 100%. Reduce it by 25%, illumination reduces by 25%.
    Everything is scaleable.

    Your example of 400-800-1200 is just a sequence of adding 400. That doesn't
    make anything linear. You could say 400-550-900-1400 and that acould be
    just as linear as long as the output is 37%, 125%, 250% _increase_ over 400.
    If you had written 400-800-1200-1600 you'd still get 100% more illumination,
    200% more and then 300% more. You can see, every addition of 400 gives you
    100% more illumination from the starting point. That's what is linear.
     
    Bruce Chang, Sep 9, 2005
    #14
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