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08/25/2005 10:08:30 AM · #1 |
Ok, so I have a grey card and never used it... I don't know what to do with it! Or maybe I do know and just don't realize it. :-)
I understand using the white side to create a custom white balance... how is the grey side used? |
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08/25/2005 10:37:35 AM · #2 |
A grey card is used to help with exposure.
Light meters are designed to figure out exposure values that will render the spot or scene that is metered a medium brightness. So if you take a picture of snow on a sunny day, your camera will clamp down and make the snow come out grey. To compensate, you need to open up 1 1/2 or 2 stops to get the white to come out white.
The most straight forward use is to set up your grey card in the light your subject will be, set your camera to spot meter mode and then meter off it - your camera will set the exposure for that card to come out nice and grey.
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08/25/2005 10:38:44 AM · #3 |
You can use it for exposure...set the card next to your subject and get a reading from it.
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08/25/2005 10:39:16 AM · #4 |
Oops....yep, like Joe said. ;^)
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08/25/2005 11:19:15 AM · #5 |
| There's another thing you can do with a grey card and that is to use it in conjunction with Neat Image (not that you probably have much use for NI with the 20D). If you photograph a grey card in the same light that your subject is in, then you can use the grey card photo to build a noise profile within NI since it won't have any fine detail that could make for an inaccurate profile. Just remember to photograph the grey card with the exact same exposure settings that you will use for your subject (aperture, shutter speed, ISO, white balance, etc). |
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08/25/2005 11:24:20 AM · #6 |
The grey card can also be used to manually set the White Balance specifically for the current conditions.
Note: by using colored cards and a manual White Balance setting, you can simulate the effect of using a color filter. I believe the filter color would be on the opposite side of the color wheel (complementary) from the color on the card. |
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08/25/2005 11:28:48 AM · #7 |
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08/25/2005 11:36:00 AM · #8 |
| Using a grey card to set exposure settings is the same as using an incident light meter. In-camera meters are reflective meters, measuring the light that is reflected off of your subject. Incident light meters meausre the light that falls on a subject. |
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08/26/2005 11:27:47 AM · #9 |
| Thanks everyone... this was very helpful. I will have to try using it sometime. Next question - is it only used when the photographer is in bright light situations, or bright (white) subject matter or should it be a practice to use often? |
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08/26/2005 11:35:27 AM · #10 |
Originally posted by tfaust:
Thanks everyone... this was very helpful. I will have to try using it sometime. Next question - is it only used when the photographer is in bright light situations, or bright (white) subject matter or should it be a practice to use often? |
It's usually used in high-contrast scenese where the camera's built-in meter is tricked into either overexposure or underexposure. You can either compensate from the camera's reading, or spot meter off of your gray card.
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08/26/2005 11:56:54 AM · #11 |
Tina,
If you are going to do fair amount of shooting in the same light take the first shot with the grey card, and it will can come in very handy later with the post processing.
Raw Files: The Raw Plug-in in Photoshop has an eye dropper for you to select your mid tone... Select the grey card, and then you can batch process the rest of your images that were shot in the same lighting and the white balance will be adjusted for you automatically.
If you are shooting JPEGS: Keeping in mind that little demo I sent you with curves you would use the grey card as your mid tone to set the white balance, cause you know its is truly the mid tone.
Then you should be able to pull up your other images and while holding down the alt key (Photoshop) go to image, adjustments and curves, and your image should be set to the previous curves settings.
You can also set the white balance of your camera with a previously taken picture of the grey card (up close). This is helpful when shooting JPGES and you do not have the same post processing flexibility as you do with RAW images.
Message edited by author 2005-08-26 12:00:28. |
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08/27/2005 02:44:59 AM · #12 |
Hi
Most shots aproximate to a gray card, for example city life, green fields etc. Its only when you get those shots like a snow covered garden that the meter gets fooled that you might wish to use the gray card. Remember 5 stops of your camera cover from the blackest black to the whitest white, with gray sitting in the middle.Who chose gray, and why is it 18%? well the white is reckoned to be 95% and black 3.5%. We see things by the amount of light reflected from it. If it was less than 3.5% we would not see it. So sqr(95*3.5) is you guessed it 18%. So 18% gray is midway between. 2.5 stops either side. So a reading of snow gives say f11 then open up two and a half stops or a reading of 1/250 then slow it down to 1/30-1/60 |
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08/27/2005 03:29:40 AM · #13 |
Way back in High School when i was in photo, they pushed the grey cards big time. We only did B/W photos and i used the light to improve the pictures. But you are supposed to use it to set the light meter to. Since i've moved to PHX, I've actually been using it more, when my SRT101's shutter didnt get stuck open. Lots of awesome landscapes here.
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