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Are you shooting with a digital camera or a film camera? Don't quote me, but I've read from what I think is a reliable source that digital meters are based on 12% reflectance, while film camera meters read 18% reflectance.

 

Kodak makes 18% gray cards. Here is one source for digital gray cards: http://www.rmimaging.com/products/graycard_index.html

 

There are other cards, but since I don't shoot digital, I haven't done much research as to which is best.

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I mostly just meter off of the green grass.

 

As far as I know common calibrations are as follows

 

12% reflectance - American ANSI standard, Sekonic, Nikon DSLR's, Kodak grey card used according to instructions that come with it.

 

12.5% - a Japanese standard similar to ANSI.

 

14% Pentax and Minolta hand held meters

 

18% - Kodak grey card not used according to Kodak instructions and recent Nikon AF SLR's.

 

12% to 18% is half a stop.

Manufacturing tolerances can be 2% of reflected light either way.

Differences of 0.66 stops between some meters is unavoidable.

 

/Clay

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Back 15 or so years ago, I had a paint store sell me a gallon of flat wall paint just the right color according to their computer. I painted several boards some up to two by three feet and others quite small. I must have 9 tenths of the can still sitting around somewhere -- unless during the recent cleaning of my basement while I was away, it was tossed. You don't need to get that much paint. A quart will do you for years and years.
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The usage of a "grey card" can be for several reasons. <BR><BR>ONE is just neutral object for a color printer to force an image to be closer to neutral. It can be the the reference object or card thats used to force "neutral calibration" with a Phase One scan back. In these two cases one wants a neutral grey object; the percentage reflectance is not so important. <BR><BR>The second reason a grey card is used is for exposure. Grey cards came out beforen WW2; before the asa speed system of WW2 even. Folks new to photography think that exposure meters and film speed systems magically came out one day; with no evolution. :); they forget about tungsten bulbs, the Kodak speed system, the Weston film speed system The reason cards are often 18 percent is its 5 times a the standard 90 percent side; ie the white side of graphics arts card used in early process camera work. The white card allows the early meter to move off of zero :) and thus one gets a starting point with asa 3 to 6 films. The reason its an integer; ie say "5" is one is exposing your process cameras negatives and blowbacks in seconds of exposure. A meter that read 4 seconds with the white card means 20 seconds as the trial exposure; ie the grey side. Think pre ww2 in a darkroom' with a crude meter that has a super low sensitivity. Today many folks think the 18 % number is some deeply thought out number; the reflectance of Britneys face; the reflectance of a 1961 Plymouths JATO taillight pods; the percentage of peek a boo hair of a todays teenager or Veronica Lake. .<BR><BR>The nikon school in 1969 had one using your palm and adjusting a stop. I think it was John Slack who mentioned this.
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  • 4 weeks later...

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