Why does Kodak say to compensate their graycard?!

Because "middle grey" is 13%, while the card reflects 18%.

Why don't they make the card 18%, like the meter expects, then? Seems dumb.

Also, why is the correction factor a function of the actual subject's brightness? Shouldn't it be that you just shift to compensate your meter for 15% reflectance and leave it at that? That would be some compensation level 'n' and would have nothing to do with the actual subject's reflectance.

Now I feel like I wasted my time buying this card.

Michael why don't you try running some tests? What Kodak is telling you is to:

Michael is right, it is dumb. However everybody in this thread is right, but for the wrong reasons.

Kodaks' advice is right, but a bit misleading and it has nothing to do with metering standards or grey card characteristics. It has to do with the limited dynamic range of film.

If I meter a scene with a grey card and the subject is extreme white you'll want to decrease exposure a bit because of the limitations of photographic film rendering pure white. Same with a very dark object. In that instance you'll want to increase exposure a bit. Notice Kodak's advice indicates corrections only for extremes.

The grey card is actually right, it's just that film can't record all the brightness range in most scenes and what you are doing is "fudging the extremes of the curve" to make sure your subject comes out right.

Here's the scenario: I got outside on a bright sunny day with fresh snow fall along my my black dog and grey dog. If I use my grey card to meter chances are my grey dog will look perfect, but the snow wil wash out and the black dog will lack detail. If I decrease exposure to compensate for the snow the grey dog still looks good, but the black dog turns into a silouette. If I increase exposure for the black dog the grey dog still looks good but the snow bleaches out.

The positive side is that the grey card gives you a near perfect frame of reference to make decisions from.

my gray card doesn't suggest any compensation for mid-tone averaged scenes. it suggests biasing the exposure reading to maintain details in the extremes. it's a dull world, that finds itself painted 18% gray.

From discussions at other sites, these instructions were in Kodak gray cards until the mid 70s, then they went away for some reason.

The reason for an 18% gray card is, like someone else pointed out, that it is a standard for middle gray in the printing industry.

Meters are set for average scene brightness, which works out to something like 12.5% gray.

So there is a correction for metering off an 18% gray card. With color print film, no big deal there is enough latitude. With slide film, it is something to think about.

the last comment makes little sense, and is in fact potentially confusing/wrong unless qualified as pertaining to an evaluative metering system only. a spot or incident meter is calibrated against a standard, which must be known and referenced to be of value.

evaluative/matrix/weighted metering can reflect an arbitrary assessment of average scenic values. statistically, I would think this is a bit lighter than 18% gray (maybe not). the important thing is to characterize your lightmeter through simple experimentation and compensate accordingly.

Roger Hicks did some checking and found that when the instruction sheet for the Kodak grey card was revised back in '70s, someone inadvertently left off that part about compensating. Now it's back.

Scott's right of course. A grey card gives you the right exposure for a mid toned subject. If you have a black cat on black velvet and you want to keep any detail in the image, you have to overexpose a bit since film (especially slide film) doesn't have the dynamic range to record much detail at 2 to 2.5 stops under (or over) exposure. Similarly if you are shooting a showshoe hare on snow and you want detail in the highlights, you have to underexpose slightly from the grey card reading or you'll blow out the highlights.

It's similar to the "sunny f16" rule, which is more like "sunny f19" for white subjects (anyone who's shot snowy egrets in sunlight may even prefer the "sunny f22" rule) and "sunny f13" or "sunny f11" for dark subjects, when you want to retain detail.

I always over expose for very bright scenes, like snow, white buildings, etc...1/3 to 1/2 stop for slide film.

I was taught that the meter in your camera was calibrated to be close to an 18% medium gray. When reading a very bright scene, the meter will want to decrease exposure to get it close to that 18%, thus giving you an under exposed picture.

However, if you have a very bright subject against a dark background, you will have to under-expose by 1/3 to 1/2 for slide film, which darkens the background but properly exposes the subject. For a dark subject against a very bright background you have to over expose, which of course washes out the background.

Your grey card is just a starting point. You should compensate your metering because many subjects and lighting conditions reflect more or less than 18% of the light.

What I was trying to get across before, is that typically meters are calibrated for about 13% gray, rather than the 18% of the card.

Scott and Bob are bang on with this one. There's an excellent book called Perfect Exposure by Roger Hicks/Frances Shultz that gives a very good explanation about all this rule of thumb kind of compensation. John Hicks - any relation? if so pass on my thanks to the authors for a thoroughly useful text (although some chapters go way over my head!)

What I was trying to get across before, is that typically meters are calibrated for about 13% gray, rather than the 18% of the card.

We've been through this before, but I can't remember what thread it was or if it was kept around. In any case, my Minolta Autometer IIIf manual states that it is calibrated to 18% gray, and my Polaris meter matches the Minolta readings exactly. Unless someone can show me a manual or printed reference that states otherwise, I'll have to assume most handheld meters are indeed calibrated to 18% gray.

I think Phil Davis in "Beyond the Zone System" puts forward some arguements as to why he thinks some meters may be (or should be?) 13% gray calibrated - or it could be that he thinks 13% grey is a mid-tone. I forget the details, though I have some memory that it might be more applicable to B&W Zone System work than shooting slides.

Good ghod, not again.

Yeah, BTZS by Davis mentions the "~13% gray" notion. It follows from the contrast of B&W negative film and how much dynamic range it can "store". Basically, the mid-point of density range of the film maps to a different point in the subject brightness range as the contrast and speed of the film changes. If I recall, this was just a theory thing. In practice, once you have calibrated your setup, any differences in what your meter assumes (18% gray) and reality have been absorbed into your model.

On the assumption that few people will have the patience to read through the entire thread Matthew kindly posted the link to, here's the relevent quotation, provided by Gerry Siegel:

Now you got me curious. Minolta IV users manual, page 3 says: " Standard reference subjects may have a reflection factor somewhere between 12% and 26%. Minolta bases its readings on a reference subject with an 18% reflection factor." Sekonic Studio Deluxe L-398 page 2: " it is designed around a standard reflectivity of 18%, which has been derived through measurements of various subjects throughout the seasons of the year." My Gossen Luna-Pro booklet doesn't say what it uses as a constant. Well I plan to call 18% a decent working hypothesis anyhow.

'Nuff said?

For those of you still convinced that you must compensate for the reflectivity of a taget based on metering concerns rather than film limitations I have one question: how would I meter a checker board?

In short, the reflectivity of a target has nothing to do with it. It's the ratio of the reflectivity of different objects that you are trying to capture on film in the first place. A grey card gives you a starting point - it's that simple.

Yes, camera meters vary, but it still doesn't change the fact of what a grey card tries to accomplish. If you were to freeze a typical camera scene in time, convert it to monochrome and swirl everything together you'd (in theory) come up with something close to 15-20% grey.

Camera meters, regardless if they are a Nikon F5 or Pentak K1000 *CANNOT* know what the reflectivity of a target is without first knowing the intensity of the light source, and that's not really possible. The metering algorithms only guess. That's why I keep pushing for less experienced photogs to learn how to use a grey card first, the theory behind it, then start relying on complex metering systems that are only trying to do guess what the humble piece of cardboard is actually doing.

The origin of the "13% myth" may be BTZS (Phil Davis):

"The old Weston Master meter, made famous by Ansel Adams and Minor White, identified the normal subject range as 7 stops and set the midpoint of that range as 3 stops from the top, which corresponds to an effective middle gray calibration of 12.5%. The ANSI standard for calibration appears to support this, although it allows individual manufacturers considerable freedom to chose their own values"

In the end, of course, it doesn't really matter. If your meter gives you the results you want, who cares how it's calibrated.

Tempting though it is, I shall keep away from the technical side-track, and refrain from commenting on the howlers in the generally excellent BTZS.

To the original question: follow the Kodak instructions to the letter. Examine the results carefully. If the results are not what you expected, or want, then adjust your methods accordingly. This might happen, for example, because your definition of 'normal reflectance' differs from that of Kodak, or your particular grey card, or your meter, or your film, or...

Michael, yes a gray card gives you 18% reflective reading, but kodak's advice is about 100 years old, to use a gray card like they say, point it at the camera, in the same light as the subject, is why they want you to compensate your expouser. You should meter a gray card that faces the source.than recompose your shot with that reading. See the video, Dean Collins on 3 Dimensional contrast, it cant be beat for correct metering advise. dave

The compensation has nothing to do with how you hold the card. The only reason you need to compensate is the limited latitude of (color slide) film as has been explained further up in this thread. When you only have a range of 5 stops, you can either have detail in the white highlights or details in the black shadows, but you can't have both whether you point the card at the camera, the light source or fall to your knees and point it at Kodak headquarters in Rochester, NY.

Check out Bahman Farzad's website which plugs his book on spotmetering and use of the gray card. www.spotmetering.com

According to my Nikon School handbook from a few years ago, the palm of your hand (assuming you are caucasion), reflects approximately the same as an 18% grey card.

Just in case you need one and don't have one with you.

Possibly, but the general rule the the palm of the average caucasian hand is 1 stop BRIGHTER than a mid-tone, or to put it another way, around 36% gray. Are you sure you're reading the Nikon Handbook right?

You are correct, Bob. I didn't read far enough. Paraphrasing, it says, take a reading off your palm and open up 1 stop.

I've never done it, or used a grey card for that matter. I find it easier just to meter and bracket, or spot meter for high contrast scenes.

Compensating for overly bright scenes is one of the hardest things for me to remember. If it looks like it will be a problem, nowadays I just use fill-flash...but that's another can of worms.

Michael: I didn't get in on this soon enough, and I don't have time to read all the responses, but the essence of the situation I believe is this: The intensity of light that your camera/meter sees is a function of the source-light (sun, etc.) AND the reflectivity of the subject. If you use a gray card, you are only supplying a standard for "reflectivity". Since you could be looking at a subject in a wide range of ambient "source" situations, you have to compensate or "compromise" your reference accordingly. Another way to look at it is this: Do you always want your medium-gray card to appear as a "Zone-5", contrast wise? Or do you want it to appear as a "Zone-6" for example, as it would in bright sun. Your camera will always try to put it in "Zone-5", and so you may want to "compensate".