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Old Sep 28, 2004, 3:33 AM   #1
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As a matter of interest - does anyone know what a correctly exposed 18% gray card's color temperature would be???:?
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Old Sep 28, 2004, 3:54 AM   #2
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If I understand it correctly, the gray card is used to discover the color temp of the ambient light. Hence, the gray card could yield any color temp depending on the light with which it was exposed.

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Old Sep 28, 2004, 9:36 AM   #3
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Color temperature is a simplified way to characterize the spectral properties of a light source. What exactly are you trying to determine?
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Old Sep 28, 2004, 9:51 AM   #4
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The grey card is neutral in color - it has equal amount of red, green, and blue. ie R=G=B which means you can also use it to set the white balance of your light source.

Ditto with a 'perfectly' white card (R=G=B= 0), which some white papers are not!
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Old Oct 4, 2004, 8:26 AM   #5
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First, let me explain where I come from.

I am an Afrikaans speaking (so please excuse the errors) South African, owner of a medium sized IT company (extremely small according to American standards) whose hobby (computers) became my occupation. I had to look for another hobby and decided on photography but recently changed to digital photography.

Although I did a lot of research on the Internet and read thousands of opinions, expert tests and articles in magazines I decided on what I want and did not worry about other people's opinions about the hardware.

I bought the best equipment I could afford and that I liked.

That includes the following:

EOS D1 Mk II;
EOS 20D (Body only);
Canon XM2 Video Camcorder (PAL version of the American GL2);
50mm f1.4 USM;
35mm f1.4 L USM;
17-40mm f4 L USM;
24-70mm f2.8 L USM;
70-300mm F4.5-5.6 DO IS USM;
100-400mm f4.5-5.6 L USM IS;
100mm f2.8 EF USM Macro lens;
550EX Flash;
MT-24EX Macro twin light;
TC-80N3 Remote controller;
Angel Finder C
ZR-1000 remote controller for the camcorder
2 Manfrotto tripods (one for the camcorder and one for the DSLR's)
Extra batteries and chargers for all cameras
4 x 2GB EF cards
2 x 2GB SD cards for the Mk II
(LC-4 Wireless controller on order; 580EX on order; BG-E2 Battery grip for the 20D on order)

But to own lots of nice photographic equipment does not mean that I am a pro. As a matter of fact I have no intention whatsoever of becoming a pro – I just want to take nice photos to show my family.

Because I am not a pro there were a couple of things about digital photography I did not understand, like white balance and the crop factors (1.3 in the case of the Mk II and 1.6 in the case of the 20D).

The 18% grey card was a source of total confusion because I was under the impression that if you take a photo of a 18% grey card as a reference point, then you do not have to worry about white balance any more. Surely (according to my reasoning) a properly exposed 18% grey card would have a certain temperature in Kelvin?? So why not rather choose the temperature instead of going through all the trouble to take a photo of a 18% grey card which is in any case unavailable here in all the camera stores I tried. I only know now that the card must be photographed whenever the light changes which just complicates the matter. So now I make use of the standard white balance choices on the cameras.

The next matter is the crop factor which I will leave for another post as this one is already to long.






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Old Oct 4, 2004, 8:55 AM   #6
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All I can say is WOW! For just a hobby you have some nice stuff.

As for the 18% gray card this is a tool used to white balance your camera. You can white balance with anything you want (white wall, piece of paper, etc.) and with any color you want too but remember all this will change the look of your picture (more so with the colors; research warm cards.) But since you are shooting digitally and you have quite a bit of storage I would suggust shooting in RAW format. With RAW mode you can adjust the color temp after the shoot (post processing) which I like better.
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Old Oct 4, 2004, 9:58 AM   #7
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Nico wrote:
Quote:
Surely (according to my reasoning) a properly exposed 18% grey card would have a certain temperature in Kelvin?? So why not rather choose the temperature instead of going through all the trouble to take a photo of a 18% grey card which is in any case unavailable here in all the camera stores I tried.
... and that's the problem which everyone is trying to explain to you -> the temperature in Kevin pretty much varies with the light source reflected off the card and not what the card is made of itself

The other thing that an 18% gray card helps is in setting the exposure, unlike the camera's meter which can be fooled by the brightness of the subjects! :?
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Old Oct 4, 2004, 10:09 AM   #8
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Thank you guys - I'll shoot in RAW with a small .jpg attached.

I am busy formulating my crop query and as soon as I know how to post smaple photos I will let you know because that is the only way how I can explain the matter.



Thanks again
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