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Photo Forum / Film Photography / Darkroom / March 2006did I make a useable "gray card"?
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 Sounds like it. > I live WAY out in the boonies with NO photo stores around so: > [quoted text clipped - 5 lines] > > Nat > 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"? 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.  SignatureNicholas O. Lindan, Cleveland, Ohio Consulting Engineer: Electronics; Informatics; Photonics. To reply, remove spaces: n o lindan at ix . netcom . com Fstop timer - http://www.nolindan.com/da/fstop/index.htm >I live WAY out in the boonies with NO photo stores around >so: [quoted text clipped - 7 lines] > > Nat 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. Signature--- Richard Knoppow Los Angeles, CA, USA dickburk@ix.netcom.com 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. Signaturedarkroommike > I live WAY out in the boonies with NO photo stores around so: > [quoted text clipped - 5 lines] > > Nat > 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)....oh heck ... it's fine ... never > mind. > > So find what works.... 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) >> Probably not, the Gray Card (my caps) reflects about 18% >> white light but [quoted text clipped - 19 lines] > Oxford, AR > (please remove CLOTHES to eee-mail) 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. Signature--- Richard Knoppow Los Angeles, CA, USA dickburk@ix.netcom.com > 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. SignatureNat nhoclothesop616(at)yahoo(dot)com Oxford, AR (please remove clothes to eee-mail) 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 >>>Probably not, the Gray Card (my caps) reflects about 18% >>>white light but [quoted text clipped - 25 lines] > pretty close. Devide the reading by 5 or multiply the film > speed by 5. Signature__________________________________________________________________ Bogdan Karasek Montréal, Québec e-mail: bkarasek@videotron.ca Canada "Wovon man nicht sprechen kann, darüber muss man schweigen" "What we cannot speak about we must pass over in silence" Ludwig Wittgenstein ________________________________________________________________ it means it is not 18%. maybe after a few days in your garb? 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. > hm... did you wash your hands first ? > ;-) Now and then. > BTW I'd use a non-reflecting gray paint and make it cover the card > fully instead of spraying partially covering black paint. H'm...that's probably a good way to go, but I enjoyed fiddling with it to get it just right. Nat |
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