Gray Card for Digital Cameras

[sanyasi]

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I have never used a gray card, but see references to them all the time. I've always seen the 18% number associated with them. When I went to several web sites for retailers, I found reference to a Robin Meyers Digital Gray Card, with the following statement:

 

"The Digital Gray Card is designed for digital photographers only, as it is not an 18% gray. Reflectance is 30-37% (based on the light source) which will create inaccurate readings with film camera light meters."

 

I don't understand what they mean. Do they mean any gray card (even 18%) ones will work with a digital camera, but don't use this one with film cameras? Since I am working with an M9 (and other digital cameras) should I limit myself to this product or do other types of gray cards work?

 

A helpful explanation would be appreciated.

 

Thanks

 

Jack Siegel

[jaapv]

It means, as is becoming increasingly clear, that the film way of measuring exposure is not correct for digital cameras. For a good explanation see the April issue of LFI.

[Jeff S]

This is why I carry an incident light meter if conditions are tricky.

 

Jeff

[giordano]

A helpful explanation would be appreciated.

 

Traditional 18% grey cards were developed to provide an artificial mid-tone for exposure measurement with B&W film. There's nothing magic about 18% except that - speaking loosely - it happens to be the average reflectance of the sort of average scene for which almost all reflected-light exposure meters (include TTL meters on both film and digital cameras) give an averagely correct exposure. In a nutshell, the idea is point your meter at an ordinary scene or point it at a grey card in the same light, and you'll get the same result.

 

A secondary use of grey cards came along with colour prints. If you include a grey card in the scene, the person making the print can adjust the colour filtration on the enlarger knowing that the card should come out a neutral grey. Then other photographs taken in the same light can be printed with the same filtration.

 

The "Robin Meyers Digital Gray Card™" is designed only for the second purpose, to be a neutral grey reference colour - which with a digital camera one uses for setting manual white balance.

 

Because it's not intended as a reference tone for exposure metering Meyers chose 30% reflectance rather than 18% (there's an explanation, which didn't entirely convince me, at Robin Myers Imaging: Digital Gray Card FAQ). One can of course use it in exposure measurement simply by compensating for the nearly 1 EV difference between 18% and 30%. But IMHO it's always simpler and better to use an incident light meter.

[wparsonsgisnet]

If you are concerned about white balance, you might like to get the WhiBal card.

 

I use this and find it indispensable. They come in different sizes and small prices.

[earleygallery]

Exposure and colour balance are two separate issues, these digital grey cards are only for colour balance.

 

In addition to a traditional grey card, you can also meter off green grass or something in signal red (like a UK post box) as they are approx the same as a grey card!

 

The point Jaap made isn't incorrect though, I find metering for digital much trickier, it's not the same as for film.

[ho_co]

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Jack--

All comments above are correct.

 

If you're using the card to set exposure with a hand-held meter, you want one with 18% reflectance.

 

If you're using the card to set white balance, you want one that is color-neutral, like the WhiBal Certified Gray Card for White Balance.

 

 

Some 18% gray cards are not color neutral and come with the notice to use them only for setting exposure, not white balance;

while on the other hand, the card you mentioned tells you to use it only for white balance, not for exposure.

[sanyasi]

Thanks all.

 

As you might suspect, I am focusing on improving my exposure skills, which led me to the zone system, which then led me to trying to translate black and white into color. I read about using green grass (trees also work), blue sky, and red bricks as midtones. Without much effort, I've seen much improvement, although the shortcut rules don't always work. The most troublesome so far has been red brick--too many shades of red. Also have started to use a meter, although not all that practical for walking around photos.

 

Best

 

Jack Siegel.

[earleygallery]

Jack, buy yourself a light meter which takes incident readings, that is you read the light source rather than the subject. It's very practical for 'walk around' photos as you only need to meter again as and when the light changes. You soon learn to know instinctively how much to allow for shade etc., and don't forget Sunny 16

[wparsonsgisnet]

The way I use the WhiBal card is to take my pictures, as usual, trying to meter appropriately and then to add an additional exposure with the WhiBal card in the scene. I use the last to set the wb before processing the image I wish to work on. I notice in C1 that when I set the wb first, the image seems to snap into focus. It's an eerie feeling.

 

Because of all the controls in C1 v5 Pro (to which I upgraded recently based on info here), I find that exposure control is handily corrected using the HDR sliders, among others.

 

In reference to my previous b/w darkroom work, I find in digital that I can recover much of what I just could not print before. I like this part.

 

In terms of color, I always found slides very difficult when the light range was too big, In digital, this problem goes away for me.

 

Other than those two observations, I continue to struggle with my color balancing and control. I am getting a higher percentage of good shots than I used to with film.

 

Feels good, tho. I also like working with Leica glass in a digital domain.

[sanyasi]

Jack, buy yourself a light meter which takes incident readings, that is you read the light source rather than the subject. It's very practical for 'walk around' photos as you only need to meter again as and when the light changes. You soon learn to know instinctively how much to allow for shade etc., and don't forget Sunny 16

 

Thanks. I did that last week and have been taking light readings everywhere to develop that second sense.