did I make a useable "gray card"?

Discussion in 'Darkroom Developing and Printing' started by nat, Mar 1, 2006.

  1. nat

    nat Guest

    I live WAY out in the boonies with NO photo stores around so:

    I lightly sprayed a white card with black paint until my reflected-light
    meter read it the same as the meter (with the incident light bubble on it)
    read the light source (sun) .

    Have I now a usable "gray card"?

    Nat
     
    nat, Mar 1, 2006
    #1
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  2. nat

    UC Guest

    Sounds like it.
     
    UC, Mar 1, 2006
    #2
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  3. Yes.

    You can use just about anything as a grey card if you are willing to
    'calibrate' it:

    o Meter a white sheet of paper and meter a 'typical scene' or measure
    the incident light. Note the difference in the reading from the sheet
    of white paper - this is a the 'calibration factor'. Use the white
    paper as a grey card and apply this calibration factor to the
    meter reading of the grey card.

    o One's hand makes a good grey-card substitute: meter the palm of the hand
    and open up one stop.

    A 'neutral' grey card - where the card has no color - is a sometimes useful
    thing to have in color photography.
     
    Nicholas O. Lindan, Mar 1, 2006
    #3
  4. If it reads the same its usable. Actually, you can use a
    white card. Kodak gray cards are white on the back with
    about 90% reflectivity. White paper withou brighteners is
    around this. Simply devide the reading by 5, or set the film
    speed for five times the value you want. I think you can get
    sheets of art paper with better diffusing surfaces than the
    usual gray card. My Kodak cards have a considerable amount
    of specular reflection which makes it necessary to be very
    careful of the angle of light vs: meter.
     
    Richard Knoppow, Mar 2, 2006
    #4
  5. nat

    Mike King Guest

    Probably not, the Gray Card (my caps) reflects about 18% white light but
    also about equal amounts of the red, green, and blue components (which I
    guess is why white light is white). But your gray card is probably "gray
    enough" for the real word (assuming that the meter in your camera is
    calibrated to an 18% reflectance (and some are not) and that your camera
    meter was looking only at the card and that there was no stray light coming
    in the eyepiece of your camera while you metered the card you made and ...
    oh heck ... it's fine ... never mind.

    Real Gray Cards get dirty, change with time, etc. MacBeth Color Checkers
    aren't perfect either and are not stable over time (and I think MacBeth
    changed the standard a couple of times, too.).

    So find what works, the only problem I have with you system is that it's not
    very repeatable. Might be better to find a color of Formica that matches
    18% and but a 3x6 foot sheet and cut it up into a pile of gray cards or a
    shade of automotive primer (gray) that's close enough to live with. Or even
    gray matt board. So that you have a supply of identical cards but that's
    just me fussin' again.
     
    Mike King, Mar 3, 2006
    #5
  6. nat

    nat Guest

    Probably not, the Gray Card (my caps) reflects about 18% white light but
    Thank you, Mike, for the learned treatise. You got me thinking(?) and I came
    up with the memory of the suggestion to just use the palm of my hand for a
    target. I went out and tried it....WOW...only 1/2 stop off the incident
    reading.

    Should work OK...I wash 'em every week or so, dirty or not.

    Thanks again,

    Nat nhooCLOTHESh616(at)yahoo(dot)com
    Oxford, AR
    (please remove CLOTHES to eee-mail)
     
    nat, Mar 3, 2006
    #6
  7. You may find the back of your hand is even closer. A
    white card can be used instead of a gray card if its
    reflectivity is assmumed to be about 90%. This will be
    pretty close. Devide the reading by 5 or multiply the film
    speed by 5.
     
    Richard Knoppow, Mar 6, 2006
    #7
  8. nat

    nat Guest

    You may find the back of your hand is even closer.

    Thanks Richard. I tried that, but my old hand is so wrinkled the angle
    becomes fussy.
     
    nat, Mar 6, 2006
    #8
  9. Hi all,

    I've measured the palm of my hand against a Kodak 18% and I have just
    under an f difference. Very handy. I also have a T-shirt that I bought
    at the Kodak Museum in Rochester that is 18% grey and has 18% print on
    the back. Actually it's .5f off from the Kodak Paper Card, probably
    because the T-shirt is cotton and thus not very, very reflective.

    Regards, Bogdan

    --
    __________________________________________________________________
    Bogdan Karasek
    Montr‚al, Qu‚bec e-mail:
    Canada

    "Wovon man nicht sprechen kann, darber muss man schweigen"
    "What we cannot speak about we must pass over in silence"
    Ludwig Wittgenstein
    ________________________________________________________________
     
    Bogdan Karasek, Mar 6, 2006
    #9
  10. nat

    nailer Guest

    it means it is not 18%. maybe after a few days in your garb?
     
    nailer, Mar 6, 2006
    #10
  11. nat

    fons Guest

    hm... did you wash your hands first ?
    ;-)

    BTW I'd use a non-reflecting gray paint and make it cover the card
    fully instead of spraying partially covering black paint.
     
    fons, Mar 20, 2006
    #11
  12. nat

    nat Guest

    hm... did you wash your hands first ?
    Now and then.

    H'm...that's probably a good way to go, but I enjoyed fiddling with it to
    get it just right.

    Nat
     
    nat, Mar 22, 2006
    #12
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