what is a grey card, and for what purpose is it used in photography?

Answer 1

The answers you received so far are all partially true.

A grey card is made up of 50% black pigment and 50% white pigment. It has a reflectancy of 18%. light meters are calibrated to give you the proper exposure to render an 18% grey card when they average the light, or if the light reading for the subject is taken directly off the grey card. When processing B&W film, you can use a densitometer to determine if your development process is giving you the correct density for an 18% grey card. If it is higher in density you are developing too long or at too high a temp and the opposite is true if it is too low in density.

They are also neutral and do not reflect a tint when properly exposed for and filtered when color printing. You can, for example, shoot an 18% grey card on the first roll of color film and then if all the remaining images were shot under the same (and correct) lighting conditions, you should be able to color balance for the first frame with the grey card and have balanced images for the remainder of the roll. This works especially well when shooting in studio situations where you have the same light frame after frame and are shooting to match a color for a client. You can also use the same densitometric procedures for color film to make sure that you are not over or under processing your film or to check for contaminated chemistry.

Answer 2

A grey card ensures that you will be getting the right exposure. It is used in situations where a camera's meter can't get it right. For most cases, the camera's "P" mode with full matrix metering will get it right reasonably. A grey card is more accurate however.

Camera meters render all images as a neutral gray, which is fine for most neutral situations. However, in high contrast situations (outdoors), the meter can be fooled. For example a subject with a very bright background, or even more extreme, a subject with snow in the background. The camera does not know that you are photographing snow...so it will come up with an exposure to make that snow grey! The grey card sets the baseline for the camera.
To use the grey card, you just have the subject hold it (or your assistant) to have it face the camera from your subject's position...reflecting the light source back to your camera. Then, use the exposure readings taken from the grey card (using a spot meter if your camera has it). It is very easy to use.

Answer 3

They are to gage a proper exposure with black and white photography. If you take a light meter reading off of true grey in the light conditions you're about to shoot, you should get a good exposure of both white and black in the frame. You can do this by holding the grey card in front of your lens and setting the exposure if your camera has a built in light meter.

It doesn't really have anything to do with contrast or white balance, as that can all be done in the dark room. It's all about getting the proper amount of exposure on the negative. Too much white = equals a heavily exposed negative that will be a pain to print / too much black = a thin negative with no "information" on it to print.

The more I think about it, the grey card is still rellevant in color photography; as it's using the same light metering conditions.

Answer 4

The grey card is the closest color to neutral so when you focus your camera color settings on this card , your colors should come out as purely as possible. To experiment, try setting colors with a grey card and then a card of anothe color, say yellow or blue. You'll see "wierd" color casts with the non-grey cards!
Nev

Answer 5

You get the enjoying cards, modern-day in sizes approximately 4x7 and 8x10 in finished digicam shops. in case you do not have a digicam keep on your city, you may get them on line from between the great properties. 50% isn't obtainable and in case you like a type of, you will ought to make certain the thank you to make one your self.

Answer 6

They are used for white balance and contrast. Much more info: http://home.nc.rr.com/tspadaro/The_Grey_Card.html