The gray card

Grandpa Ron

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I am still trying to get a a better understanding of proper exposure for Black and White film. Recently I have been reading about the use of the gray card.

If I understand correctly, if you take a gray card reading in front of the subject you wish to photograph, that subject should develop as the mid-tone on the negative, unless it is shiny or otherwise much brighter than its surroundings.

That would mean the remainder of the photo could be too light or too dark depending on the the subject's brightness compared to it surroundings. For example a gray card reading of a subject in the shadows could cause the remainder of the photo to be to light.

I this correct?
 

Ysarex

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I am still trying to get a a better understanding of proper exposure for Black and White film. Recently I have been reading about the use of the gray card.

If I understand correctly, if you take a gray card reading in front of the subject you wish to photograph, that subject should develop as the mid-tone on the negative, unless it is shiny or otherwise much brighter than its surroundings.

That would mean the remainder of the photo could be too light or too dark depending on the the subject's brightness compared to it surroundings. For example a gray card reading of a subject in the shadows could cause the remainder of the photo to be to light.

I this correct?
Correct. The gray card knows nothing about the contrast/dynamic range of the scene. Reading a gray card is a lot like taking an incident meter reading. It's accurate for an average scene. Trouble is what about a scene that isn't average. That's why you see all the Zone System devotees with spot meters. Spot meters allow them to measure discreet tones and calculate the scene total DR and decide where to go then with that info.

A more casual approach without a spot meter is to learn to recognize the variations in lighting from average and then learn what to do when you encounter them. Average scene contrast is a front-lit by sunshine landscape. An incident meter or gray card reading in the sun should give you a good exposure. But move the sun to the side and that's no longer average -- contrast just went up and shadows are larger and darker and highlights are relatively brighter. How do you want to record that and then how to meter it and set an exposure becomes trickier. If you meter the gray card in the sunshine you get the same reading as you would for a front-lit scene with less overall DR.

Amateurs look through their cameras and see their subject. Photographers look through their cameras and see how the subject is lit.
 

ac12

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quote:
If I understand correctly, if you take a gray card reading in front of the subject you wish to photograph, that subject should develop as the mid-tone on the negative, unless it is shiny or otherwise much brighter than its surroundings.

That would mean the remainder of the photo could be too light or too dark depending on the the subject's brightness compared to it surroundings. For example a gray card reading of a subject in the shadows could cause the remainder of the photo to be to light.
...end quote

Yes and no.
This is goina be long.

As @Ysarex said, metering off a grey card is independent of the actual scene, just like using an incident meter.

Definitions:

Incident:
With an incident meter, you are measuring the light falling on the card or scene.
You are IGNORING the scene.

Reflective:
When you meter a scene either TTL or direct meter, you are metering the light that is reflected from the scene.
The reflected meter is calibrated to give you an exposure for the "average" scene of 18% reflectance.

Grey Card:
When you measure a grey card you are measuring the light that is reflected from the grey card. So you use a reflected meter.
BUT, you are measuring a card (not the scene) that has a fixed reflected value (18% grey).
So in effect, it works like an incident meter, because you are not measuring the light reflected from the scene.


"if you take a gray card reading in front of the subject you wish to photograph, that subject should develop as the mid-tone on the negative"

Nope. This is confusing reflected and incident.
By your statement, both a black cat and a white dog would have the same mid-tone density on the negative, and look grey.
That is what happens when you direct meter the reflected light from the subject.
This is because the meter tries to expose everything to be 18% grey. So it overexposes the black cat, and underexposes the white dog.

Metering a grey card is independent of the scene/subject. You are metering the card, not the subject. So the subject density on the negative will be independent of the meter.
The black cat will have a low density on the negative, because there is less light reflected from it.
And the white dog will have a high density on the negative, because there is more light reflected from it.

If you were metering at the beach, a TTL or direct meter would see nothing but BRIGHT, and the meter would lower the exposure so that the white sand turns grey. mid-tone/18% grey.
The incident meter or grey card method, meters the light falling on the subject, not the light reflected from the subject. So the white sand would be exposed to be white, NOT grey.
But, the Dynamic Range of the scene may exceed the DR of the film, and result in the white sand blowing out the exposure, and being too black on the negative. The grey card or incident meter has no way to determine this, because it is not measuring the light reflected from the subject.


"That would mean the remainder of the photo could be too light or too dark depending on the the subject's brightness compared to it surroundings. For example a gray card reading of a subject in the shadows could cause the remainder of the photo to be to light."

Not quite.
Remember that the subject brightness/density is dependent on the light on the subject. So how bright the subject is, has no effect on the surrounding.
- A black cat in a coal bin will be black, as will the coal bin. This will be a thin negative.
- A white dog on snow will be white, as will the snow. This will be a dense negative.
- A black cat on snow will be black, and the snow white.

However, a subject metered in the shadow is in less light than the surrounding that is in the bright sunlight with MORE light.
So in that case, the subject in the shadow will be properly exposed, and the surrounding in the sunlight will be overexposed.
Same in reverse, if the subject is in the bright sunlight, something in the shadows will be underexposed.


There is a partial fix for blown highlights.
In the film days, when I shot slides, and used an incident meter. The normal way to hold the incident meter was to point the dome towards the camera.
But for highlight issues, we pointed the dome half-way between the light source (the sun) and the camera. This biased the meter for the extra light from the sun, so the highlights would not blow out, as much. I also do this when I use the incident meter for digital.
This was because with slides, it was WYSIWYG, we had no 2nd chance. And slide film had a smaller DR than negative film.
Whereas with negative film we had a 2nd chance, to "salvage" the image in the darkroom by burning or dodging.
 
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Grandpa Ron

Grandpa Ron

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Thanks for the explanations, I does clarify the reflected light and explains the use of a spot meter.

The zone method is easy to understand but in practice, looking at a scene in full color and envisioning it as it may appear as density changes on a b&w negative is quite a challenge.
 

Ysarex

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Thanks for the explanations, I does clarify the reflected light and explains the use of a spot meter.

The zone method is easy to understand but in practice, looking at a scene in full color and envisioning it as it may appear as density changes on a b&w negative is quite a challenge.
We used a viewing filter for that. No longer available the down dirty grab was a Kodak Wratten #90 filter. Here's a link to BH where you can still purchase a B&W viewing filter: Tiffen #1 Black and White Viewing Filter The goal is to give you a better idea of how the color scene will translate to B&W. There's probably a box of junk in the bottom of one of our closets where my wife will find one after I'm gone -- not that she'll know what it is. ;-)
 

ac12

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Thanks for the explanations, I does clarify the reflected light and explains the use of a spot meter.

The zone method is easy to understand but in practice, looking at a scene in full color and envisioning it as it may appear as density changes on a b&w negative is quite a challenge.

Yes I had that problem often.
My common problem was, a person with black hair in front of dark green plants. That was a bad idea. The hair and plant leaves are about the same dark gray/black tone, so the hair merges/disappears into the leaves. :eek-73:
I made that mistake often.

Without using a B&W viewing filter, we used a plain red filter to try to teach us to view in mono tone.
But the red filter will darken blue sky and lighten red, so it distorts what you are looking at. So it did not work if you were critical about the final image.
 

maris

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Grey cards are useful and a bit tricky.

Mid-grey was arrived at by surveying many people to select a tone half way between black and white. Their choices converged on a grey tone that reflected 18% (amazingly not 50%!) of the light falling on it.

Modern grey cards you can buy are surprisingly sensitive to turning or tilting in terms of the actual reflectance they deliver. They are not Lambertian reflectors so having them square on to the optical axis of the camera helps consistency.

If a light-meter is calibrated with the true film speed determined by user testing then something useful happens:
Such a meter reading off a grey card will suggest an exposure that will deliver an amount of light in lux.seconds equal to 10 divided by the film speed.
This exposure will, given normal development, produce a negative density of about 0.65.
This density when projected onto middle contrast photographic paper will deliver a mid-grey tone if the enlarger exposure is just enough to make unexposed parts of the film print black. From grey in the subject to grey in the print; the circle closes nicely.

Of course things in the subject space darker than the grey card will now be represented by low negative densities and will print dark.
Things in the subject space that are lighter than the grey card will be represented by high negative densities and will print pale.

Sounds good BUT using the grey card to get grey in the print does not predict how dark or light the other tones will turn out; maybe too dark and too light ... or the opposite! That's what an accurately calibrated spot-meter that reads direct subject luminances can do.
 

Warhorse

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I have read that Nikon (as well as some other manufacturers) actually use a 12% grey as a base for correct exposure. Can someone here who knows more than me explain this?
 

Ysarex

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I have read that Nikon (as well as some other manufacturers) actually use a 12% grey as a base for correct exposure. Can someone here who knows more than me explain this?
Here's some reading: What is middle grey and why does it even matter? - DIY Photography

and:

 

ac12

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Grey cards are useful and a bit tricky.

. . .

Modern grey cards you can buy are surprisingly sensitive to turning or tilting in terms of the actual reflectance they deliver. They are not Lambertian reflectors so having them square on to the optical axis of the camera helps consistency.

. . .

This is why I like the incident meter dome. it is less fussy, for someone like me.
 

Warhorse

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Here's some reading: What is middle grey and why does it even matter? - DIY Photography

and:

Thank you, that's as good an explanation I have ever heard.
 

mrca

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Ron, unlike digital where we protect the highlights from blowing out, b&w film is the opposite, under exposure blocks up the shadows and there is tons of range into highlights. So to protect shadows, a reading with an incident meter can be on the shadow side with dome aimed away from subject towards the shadow. That will insure the shadow area isn't under exposed. Taking a reading at the chin with dome to camera is measuring mid tones and a reading from highlight side protects highlights. For portraiture I want skin tones properly exposed and since if there is a main and fill light, they usually overlap, I take a reading where the lights overlap, eg, the shadow side cheek. If you place your grey card there and zero out, you should be on. With just one light source like ambient, just take reading where you want proper skin tone. You can spot meter with your digital camera meter just below that eye. Caucasian skin is one stop brighter than middle gray so spot there, add one stop or so of light from dead center and you are there. No need for a gray card. The palm of every race is the same tone, about 1 stop brighter than middle gray. Take a reading of the palm in front of the face, place meter one stop brighter than dead center. Since a meter makes everything middle gray, it darkens something brigher than middle gray so you must add back 1 stop of light using aperture, shutter speed and digitally iso. When I photo people, I also focus through the same spot so metering just below the eye adding one stop of light and hitting back button focus takes a split second and exposure is nailed and eyes are sharp. Recompose and click. And warhorse is correct, when I bought my first gray card at Kodak in Rochester in the 70's, it had a small piece of paper instructing to add or subtract light, I don't remember which. Also tilting the card can alter the reading. My most important photo tool isn't a camera or even lights, it's my sekonic spot/incident meter. Find how you like to use it, stick to it and exposure is just something to get out of the way so you can concentrate on the real purpose of the shot, the message.
 

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Ctein's "Post Exposure" has a complete discussion of the 12/18% metering issue, and why grey cards should be angled.

Some 60 years ago, I had trouble with exposure, and came across the method used by a press photographer, which mrca gave above. I stick my palm in the same lighting as the subject, take a reflected reading, and open up one stop. Perhaps I never encounter tricky lighting, but this has always worked for me.

I also downrate the film from 125 to 80 (I use FP4 Plus in large format) to ensure enough shadow detail.
.
I did use a spot meter for a while, but the results were no better and the time taken much greater. For me, it wasn't worth it.
 

ac12

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It is fairly easy (just tedious) to meter the card, shoot, process the film, then evaluate the negative.
Then adjust the ISO level on the meter up or down, to give you less or more exposure. Example +2/3 stop.
Once you figure it out, note the off-set and use that same off-set for whatever film you shoot.

In my early days, I metered off my palm, but never did the +1 stop adjustment.
But looking at my palm and a grey card, the reflective difference is rather obvious. duh
B&W processing and printing was very forgiving of exposure errors, and we could do and did, a LOT of adjustment when printing in the darkroom.

Out of curiosity, now I want to test the other grey card substitute that we used, green grass.
That would be a problem today, with football fields of synthetic turf. Light reflection is not consistent. Unlike grass, when shooting towards the sun, the sun glares off the synthetic turf, like I have not seen it do on grass (except when wet).
 

mrca

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ac12, and the palm of all races is the same 1 stop brighter than 18% gray, ie Zone VI. Lots of way to skin the exposure cat. Run and gun, spot below eye and get focus and meter 1 stop brighter, recompose shoot. Takes longer to say than do. And both focus and exposure are dead on, not counting on the camera to make a guess. For portraits with time, incident meter. Out doors, dont have to walk to subject if I am in same light, just orient the dome towards camera with my arm extended. How many carpenters do you see without a tape measure on their belts? The meter is our tape measure. Seems like novices spend much time and worry over something as simple as exposure. These days there are phone apps that apparently are pretty accurate, certainly better than the camera pulling exposure out of it's .... usb receiver.
 

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