Gray/Grey Cards for Exposure in Photography

ziggy53

In another recent discussion, the topic of Gray/Grey Cards, used for exposure determination, came up. I started this separate discussion rather than steal the other thread's direction.

ziggy53

@pathfinder said:
...
While I think this is very close to what Ziggy is suggesting also, I think using a grey card ( is it 16 or 18% grey?? I have seen both numbers ) without exposure compensation is the answer they were expecting.

Preface: I just searched and it appears that Kodak no longer manufactures Gray Cards, so I could not find the original reference they had to their card specifications. I also cannot find my copy of the documentation which came with my package of Kodak Gray cards.

This is pretty tangential to the original poster's question, but perhaps it will explain the situation better for all, including the original poster.

A long time ago, before color film even, Kodak was the only company to supply photographer's aids to correct exposure. The Kodak Gray Cards, Kodak Exposure Guide and several other products from Kodak, all included gray targets on extremely heavy card stock. The targets were designed for 18 percent reflectance, which was a compromise in suggested values from expert sources at the time (a consortium), and suggested that this value represented a photographic "middle gray".

The links for both B&H and Adorama both still reference this value for the cards:

B&H Kodak R-27 Gray Cards

PRODUCT HIGHLIGHTS

Gray Side Offers 18% Reflectance
White Side Offers 90% Reflectance

Adorama Kodak R-27 Gray Cards (No longer Available)

About Kodak 1903061

One side of the card has a neutral 18-percent reflection which can be used indoors to aid in measuring the average reflection for a typical subject. You can also use this side of the card outdoors by increasing the exposure 1/2 stop above the calculated exposure. The other side of the card has 90-percent reflection for use at low- light levels.

ziggy53

However, the film motion picture industry had another consortium regarding exposure, and decided to use a 16 percent gray/grey reflectance value for "Middle Gray". The following undated Kodak publication excerpt seems to shed some light on the 18 percent versus 16 percent confusion:

Kodak EXPOSURE TOOLS

Page 116
"An 18% reflectance represents an average of all the reflectance values in a given scene. It can be thought of as a
reflected value that falls halfway between a white object and a black object. Cinematographers sometimes meter
an 18% gray card to determine the proper exposure for a subject. The gray card serves as a reference for the
cinematographer when viewing the dailies. Using a gray card minimizes guesswork and helps to ensure more
accurate color reproduction."

Later, same page:

"• If you use your spot meter to measure something that is a middle tone (approximately 18%
reflectance), you will get a normal exposure."

... But on the following page ...

Page 117
"ANSI standard PH2.12 explicitly specifies 16% average scene reflectance as the metering constant for incident
and reflection meters."

With the explanation:

"Kodak studio photographers preferred 18% reflectance, one-sixth of a stop more than 16%,
because it provided better results. Given the superior latitude of today’s films, an exposure
difference of one-sixth of a stop is insignificant."

^^
From the above, I can only conclude that Kodak may well have started the confusion about 18 percent and 16 percent reflectance values.

ziggy53

To lend further to the confusion, this by Thom Hogan:

Meters Don't See 18% Gray

Cygnus Studios

The grey card thing got wacky when digital cameras came out (too many different companies making them). You can buy 5 cards and get 5 different shades of grey. Some like Whibal even make one set of grey cards for jepg/film and a different (lighter) one for raw.

Was 18% ever really correct? Most think that 12% is correct now, but as you pointed out, different industries have different standards. It was 2003 (if my memory serves me right) when "Expose to the right" became the talk of photography.

Outside of the fashion photographers I haven't personally seen anyone using a grey card. Everyone else switched over to white cards.

ziggy53

@Cygnus Studios said:
Was 18% ever really correct?

Both the Kodak consortium (see above reference) and Ansel Adams seemed to prefer an 18 percent gray card combined with a narrow-angle reflectance meter. (Sorry, I can't find an accurate reference for Ansel Adams just now. It's supposed to be in his book, "The Negative", on page 33, or on pages 42-43 on older copies, but my "Fifth Printing 1971, copyright 1968" doesn't seem to have it.)

Norman Koren also appears to adhere to the 18 percent value, as he says in the following link: http://www.normankoren.com/zonesystem.html

@Norman Koren said:
"In a print, ... zone 5 is subjective middle gray, corresponding to a reflectance of about 18%."

.

@Cygnus Studios said:
Outside of the fashion photographers I haven't personally seen anyone using a grey card. Everyone else switched over to white cards.

White cards are mostly used for white balance and less commonly for exposure, although I have wanted to see where photographic white lands on occasion. The Kodak cards used to come with 2 - 8"x10" and one 4"x5" card in the package. Lining up both the large cards, one facing gray side and the other facing white side, gives you both middle gray and 90 percent white spikes on the histogram. This was/is useful for some projects.

I will admit to now being spoiled by the x-rite colorchecker Passport Photo targets for critical RAW color work.

pathfinder

Ziggy, I want to thank you for this most informative discussion of 16 versus 18% grey cards. I always wondered why there were different numbers that were so small as to be almost insignificant, yet they kept popping up. Now I understand a bit more.

If you think of all the things ( accurate concentrations of developers and fixers, solutions temperatures, and whether the processing was timed by a clock, among others ) that can vary the response to exposure with film - either color or B&W - the difference between 16% and 18% really does seem to be splitting hairs to me. But there's more!! Movie camera lenses come with T stops, and still camera lenses come with F stops too...