grey card

cypilk · May 9, 2004

can someone explain to me what the grey card does in a camera.. i think it has something to do with black and white.. but i never really understood it.

voodoocat · May 9, 2004

18% grey cards are used for determining exposure and doing custom white balance in digital photography.

When you use a reflective light meter (such as the one built into your camera), it exposes for ~18% grey. When you shoot a subject that is in uneven lighting, very bright or very dark colors your exposure will be off. If you can put a grey card in the same lighting as your subject you can meter off the card and then use that exposure value.

You can also use the grey card as a reference to set white balance in the same manner you used to determine exposure.

cypilk · May 9, 2004

eh... thats confusing.. so..basically.. you're saying that in digital photography, there are 18 % grey cards.... and in film cameras.. there are reflective light meters... which does about the same?..

the light meter is off when you take a picture of uneven lighting... lets say ..a room with a lamp on and the bulb is in the picture... therefore making the picture too bright on one end and dark on the other...

what i understand is that..the camera just references white using the light meter?..

ksmattfish · May 10, 2004

It is generally accepted that light meters (in camera and hand held) give the recommended settings to render middle grey tones or 18% gray (this isn't actually totally correct, but it's always presented as such). So when you point your camera at a scene, the assumes that there is an equal amount of light and dark (making middle gray) in the scene, and gives you the recommended exposure to render a "gray" scene, of course if you are shooting color, digital or film, it will be in color. This works well in many situations, but not all.

If you are metering a predominantly dark scene, the meter is still giving the recommendation for middle gray, which will actually be an over exposure (gray is lighter than black). So to get the dark scene exposed for correct tones you must adjust the camera to under expose.

If you are metering a light scene, once again the meter tries to make it gray, so it under exposes (gray is darker than white). To get the light tones exposed correctly, you must overexpose.

If this seems confusing, then you would be helped by a gray card. A gray card is middle gray, so if you meter off a gray card in the same lighting as your subject, then you should have the proper exposure. You can set the gray card in the scene and meter off it, or have your subject hold it up.

metroshane · May 10, 2004

OK, 18% grey is half way between the blackest black and whitest white...thereabouts.

when you meter something, the camera is using an algorhythm based on 18% grey to determine what exposure to set. So you can see that if you were taking a very dark or very bright pic...the camera's meter will be tricked and mess up your exposure. To compensate you can hold up a grey card and take the measurement off that.

cypilk · May 10, 2004

hold up a grey card?..what do u mean..

like literally hold up a card?

drlynn · May 10, 2004

Yep. A grey card is a grey sheet of cardboard. You place it in the scene and point your meter at it.

cypilk · May 11, 2004

oh..but grey cards are different .. is there a standard grey card you can get at a store?..

and after i use the grey card...the camera knows what white and black is?... but once i take the grey card out of the picture..it'll go back to being "off" again

drlynn · May 11, 2004

A good camera shop will have grey cards for sale.

You check your exposure on the grey card. Say your camera's meter reads the grey card and decides on f/8 at 1/125.

Then you remove the grey card from the scene, set your camera on manual exposure, set it to f/8 at 1/125 and shoot.

It isn't a one-time thing that resets the camera permanently.

ksmattfish · May 11, 2004

cypilk said:
oh..but grey cards are different .. is there a standard grey card you can get at a store?..

and after i use the grey card...the camera knows what white and black is?... but once i take the grey card out of the picture..it'll go back to being "off" again

If you get a photographic gray card it will be 18% gray or middle gray.

Go buy one, it'll have detailed instructions on the back.

cypilk · May 11, 2004

cool.. it seems as if a lot of people use the grey card.. do a lot of people use it for almost every shot?

voodoocat · May 11, 2004

cypilk said:
cool.. it seems as if a lot of people use the grey card.. do a lot of people use it for almost every shot?

I've used mine twice for exposure. Then I got an incident meter and it works the same way but easier. Now I occasionally use it as a reference for creating custom white balance.

cypilk · May 11, 2004

i just read online.. that you don't really need a grey card.... if you just take the subject in the same light... and you take the metering off that subject...just manually adjust the camera.. to take the shot off the meter..and you should be fine... pretty good idea i say =))))))