gray card is useless?

[pierods]

Hi,

a few weeks ago I read a book about the zone system.

Since I shoot 35mm, I decided that it was only partially applicable to me, not having control of development of single frames.

I thought a gray card would help exposure anyway, so I bought one.

I screwed up a few rolls of film, and then the following occurred to me:

If I measure light by putting a gray card at the same spot where my subject is, I will have to correct exposure by keeping into account the reflectivity and the tone of the subject.

So, say my gray card says X EVs. I am photographing snow, so I know that real EVs are X + 2EVs (if I remember correctly).

Or, I am photographing coal, so I will set my meter at the gray card's EVs - 2EVs.

But...wait...if I know the correction for subject X, what's the use of the card? I can just measure off the subject and offset by what I know about the subject.

And if I don't know what the correction for my subject is, the gray card is not going to tell me how much to compensate anyway...

Same thing if I want to place object Y in zone Z. Measure off the object, compensate for its color, compensate again for the zone, done.

So am I missing something?

Maybe it's useful in studio settings? For white balance?

 

[ann]

i am not a fan of a gray card reading in the real world , a studio maybe different.

there are lots of middle gray values in mother nature's world and if you feel the need use the grass, or a clear blue sky.

without getting into a "war", i think learning the zone system can help one make better decisions about understanding values and what can be done. that is my experience, so please don't take this into a zone system vs...........

of course it is very diffult to apply with 35mm film unless one dedicates the whole roll to the exposure and development process; however, one can bulk roll short rolls.

just my .02 cents

 

[Paul Howell]

If your camera meter is calibrated correctly and you have tested your camera for your personal film speed and you meter off a gray card: snow ought to be white, grays gray and blacks black. Meters, even matrix meters, can be fooled with large areas of bright or dark in SBR.

 

[2F/2F]

You are absolutely right in your thinking that something is odd when using the zone system with a grey card. With the zone system, the grey card is pretty much only used for your lab tests, not in the "field". If you are metering off of a grey card in a real-world shooting situation, it probably means that you are NOT using the zone system, but simply looking for a measurement of the over all amount of light present at the scene, just like an incident reading.

But you are missing something about how to use the card, what it does, and why you would use it. The grey card, in theory, eliminates the need to make any adjustments from the reading off of the card (assuming you want tones rendered fairly accurately and are happy with the contrast at the scene). It gives you the equivalent of an incident light reading.

Think about it for a minute. Your reflected light meter tells you how to make *whatever you point it at* appear as middle grey. That is the only thing reflected light meters do. (Incident meters, on the other hand, tell you how to make *middle grey* appear as middle grey.) Don't think that reflected meters tell you what the "right" exposure is, or anything else. All they do is give you a reference value. Once again, they tell you how to make middle grey, no matter what it is pointed at.

You also know that your reflected light meter, due to this characteristic, can VERY easily tell you the wrong thing if you do not know how to control it very carefully. This is where the grey card comes in.

If the light meter tells you how to make something middle grey, and you meter something that you know to be middle grey (the grey card), then you will be rendering the world "accurately" on your print. Because you exposed in a way that will render grey as grey, all other tones will "fall" into place more or less how they appear. The contrast of the film you are using, and your development will, of course, cause variations, but the basic idea still holds.

Once you have more of a handle on things, there are plenty of times you might use a grey card with the zone system. I use one in studio when I am using hot lights, just to make sure I am not getting some errant reading from a weird glare or something when using my spot meter. But this is just a self checking process. I'm not metering the card and then placing its tone where I want it, like you are thinking one should do.

 

[markbarendt]

I've had great luck with grey cards. As with everything it needs a grain or two of salt. It only helps judge the light not the reflectance or the mood.

Kodak says "For normal reflectance subjects add 1/2 a stop, for light subjects decrease by 1/2 a stop, Dark to very dark subject increase by 1 - 1 1/2 a stops."

 

[pierods]

I've had great luck with grey cards. As with everything it needs a grain or two of salt. It only helps judge the light not the reflectance or the mood.

Kodak says "For normal reflectance subjects add 1/2 a stop, for light subjects decrease by 1/2 a stop, Dark to very dark subject increase by 1 - 1 1/2 a stops."

Exactly right. But since you have to know how much to correct (and the card does not say it in case you don't know) you could just meter off the subject and correct...right?

 

[pierods]

If your camera meter is calibrated correctly and you have tested your camera for your personal film speed and you meter off a gray card: snow ought to be white, grays gray and blacks black. Meters, even matrix meters, can be fooled with large areas of bright or dark in SBR.

One bizarre situation is that in situations with uniform lighting, with subjects that had the same measurement as the card, I would get the wrong exposure....

For that particular scenario, I thought that even though the subject has the same measurement as the card, only experience could have told me the right correction, thereby rendering the card useless again.

 

[David William White]

Nope

Your thinking is not correct. Say you are shooting snow or beach sand. Without the card, your 18% grey meter will underexpose the scene, and if you are shooting coal, your meter will overexpose. The point of using a grey card is to meter light reflecting off the card WITHOUT adjusting for your subject. That is the beauty of the card. Metering STRAIGHT off the card will keep your beach sand or snow properly where it is and keep your coal where it is.

One thing: The card must be getting the same light as your scene and it must fill your meter area, so fill your viewfinder with the card.

This is assuming you want your sand or coal to render in the negative as close to reality as possible, and of course assuming that your camera meter is close in calibration, blah, blah, blah...

David.

Hi,

a few weeks ago I read a book about the zone system.

Since I shoot 35mm, I decided that it was only partially applicable to me, not having control of development of single frames.

I thought a gray card would help exposure anyway, so I bought one.

I screwed up a few rolls of film, and then the following occurred to me:

If I measure light by putting a gray card at the same spot where my subject is, I will have to correct exposure by keeping into account the reflectivity and the tone of the subject.

So, say my gray card says X EVs. I am photographing snow, so I know that real EVs are X + 2EVs (if I remember correctly).

Or, I am photographing coal, so I will set my meter at the gray card's EVs - 2EVs.

But...wait...if I know the correction for subject X, what's the use of the card? I can just measure off the subject and offset by what I know about the subject.

And if I don't know what the correction for my subject is, the gray card is not going to tell me how much to compensate anyway...

Same thing if I want to place object Y in zone Z. Measure off the object, compensate for its color, compensate again for the zone, done.

So am I missing something?

Maybe it's useful in studio settings? For white balance?

 

[RobC]

Your thinking is correct. A grey card is almost totally useless for black and white photography.

And yes you do need to know how much to offset your reading of any part of your subject. There are anomalies in "The negative". The biggest one is that an 18% grey card is a zone V on AA's 0 thru X zone system. It is NOT. The proof is remarkably simple but usually overlooked because AA couldn't possibly be wrong. If 18% is zone V then Zone VI would be 36% and Zone VII would be 72% and zone VIII would be 144%. But hold on a minute, how is it possible to have 144% reflectance? It isn't. 18% is actually always approx 2.5 stops less than 100%. So in a 5 zone system going from 0 thru V, zone II 1/2 would be 18%. On a 10 zone system, 18% is between zone VII and zone VIII, and zone V is only around 3% reflectance.

So is an 18% grey card a middle grey? Yes it is. But place it in any light and measure other relative brightnesses around it and there is no guarantee that it will be the mid point unless the other brightnesses range from zone 0 thru zone V. The card should work pretty well for colour transparency which only has a range of 5 or 6 stops. For black and white film with a range of 10 stops I would suggest you bin the grey card and take readings of actual subject values. Experience will very quickly tell you how much to adjust by.

And if you have read the Kodak instructions for use of a grey card, you will see that it needs to be placed at very specific angles in relation to the light source, the subject and the camera before it reflects 18%. You can see its luminance change just by tilting it.

And if you have read AA carefully you will have seen that if different parts of the subject are in different lighting, then a grey card has no use at all.
Shadows are in different lighting than something in direct sunlight. Therefore 99.9% of sun illuminated subjects are not suitable for using a grey card to ascertain exposure. He got that right.

A spot meter has a built in and very accurate measuring system which is far superior to a grey card and allows you to measure relative brightness across areas in different lighting, which is exactly what you want to be able to do.

Do your film calibration using your spot meter and not a grey card.

[edit]
p.s. before I get slammed by the grey card users: Why does it work for some people? Well, becuase if you place it at the main point of interest and base your relative readings from say zone III to VIII, then you are using a five zone subset of the full image brightness range. That will be approximately correct but not exactly because nobody sets the card angle correctly and it does not take notice of the high and low values so problems with deep shadows and very bright highlights may occur. And if you need n- development, then since V is not the mid point of III thru VIII and N- will push zone V down maybe half a zone, then zone V could easily end up at zone IV. But its still ball park and can be saved in printing.
[/edit]

 

[pierods]

Your thinking is not correct....
David.

See previous post:

One bizarre situation is that in situations with uniform lighting, with subjects that had the same measurement as the card, I would get the wrong exposure....

Otherwise, I have to assume that the meters of my 2 F80s and on my D70 are wrong, and the various, different films from Ilford and Kodak I have tried the card with are off their ISOs.

 

[Pinholemaster]

Get an incident meter. Read the light falling on the scene. Same as a gray card.

Meters want to turn everything to 18% gray. Gray cards are 18% gray. Place your gray card in the correct light for your scene. Meter only the gray card, nothing else. Use the exposure value of the the gray card. Don't change it.

Ignore the zone system for 35 mm film, unless you are exposing all the frames for once scene.

KISS works every time. You are over thinking this.

 

[Kino]

Gray Cards are just one more tool in the arsenal -- sometimes they are applicable, other times, not so helpful.

GCs are good for incident light readings with a spot or general field meter (that doesn't have a integrating dome) when you have a subject with less than even distribution of light values.

Of course, as you indicate, you have to interpret the scene and make adjustments from your averaged reading, but it at least puts you in the ballpark.

 

[bobwysiwyg]

..of course it is very diffult to apply with 35mm film unless one dedicates the whole roll to the exposure and development process; however, one can bulk roll short rolls.

This is what I did many years ago while trying to learn the Zone System. A bit of a hassle come development time, but found it very helpful. I would, on occasion, load as few as 5 frames dedicated to a particular subject. I actually have some Pan-X in a bulk loader that's got to be 25 years old. Hmm, wonder what would happen if I shot some of it.

 

[Gerd Orfey]

For white balance?

It depends. Most grey cards are made to reflect 18% light only, but their colour might not be really grey, esp. not in any lighting situation.

Doesn't matter in bw photography, but for white balance you should ask the manual wether the grey card is suitable.


Gerd

 

[2F/2F]

Rob, it was always my understanding that the 18% grey card WAS supposed to signify the halfway point in a five-zone range; the five zones that show detail: III-VII. Not a five stop range from absolute black to absolute white, but a five stop range from as black as detail can get to as white as detail can get. Can you elaborate on your statement that you need a 0-V range for a grey card to be accurate? The way I think it through, there is no such thing as a zone at the scene; only in the print, so I don't get the 0-V statement. There is no such thing as anything below zone III or above zone VII, detail-wise to our eyes in a standard-contrast lighting situation, therefore, the grey card works. The more contrast at the scene, the harder it is for the card to be accurate, I agree. But to refer to the real world in terms of zones is not only confusing, but just incorrect. We zonies all tend to do it, although zones are values on a print; nothing else.

I would say that in order for the *most* accuracy from a grey card, the dynamic range of your scene has to exactly match the dynamic range of the print. But this is never the case, so a grey card just gets you an exposure that will land most things with visible detail in the zone III-VII range on the print.

It works entirely predictably and accurately for black and white and color film every time I use it, either as an alternative to an incident reading or for initial tests.

 

[Paul Howell]

One bizarre situation is that in situations with uniform lighting, with subjects that had the same measurement as the card, I would get the wrong exposure....

For that particular scenario, I thought that even though the subject has the same measurement as the card, only experience could have told me the right correction, thereby rendering the card useless again.

That is why in tricky lighting you bracket. But the card is not useless.

 

[Michel Hardy-Vallée]

If I measure light by putting a gray card at the same spot where my subject is, I will have to correct exposure by keeping into account the reflectivity and the tone of the subject.

Theoretically, No.

You correct your meter reading when you are metering your subject, not when you meter the grey card.

If you put your grey card besides a white object, then you are supposed to use the meter reading of the grey card without corrections. But if you are pointing your meter at the white object, then you open up some two stops.

The same thing goes for a dark object. You point your meter at the grey card: you don't correct (in theory!). You point your meter at the coal: you close down by 2 stops.

Now, some of the caveats:

• If your grey card is not exactly in the same light as your subject, it's useless.
• If your grey card is at the wrong angle from your light source, it's useless.
• If your subject reflects a lot of UV (like snow), to which films are more sensitive than light meters, then your grey card is useless.
• If your scene is VERY contrasty, your gray card is useless because you can lose highlight or shadow details without knowing it.

When I am working quickly, I prefer an incident meter to a grey card reading, or I meter my palm. When I am working more carefully, I take reflected light readings and make sure the contrast of my scene will fit in my workflow.

But often I just use sunny f/11 and to hell with the Zone system!

The one thing that made a big difference on the quality of my 35mm prints is proper development. Overdevelopment always look like crap. Good processing won't save an underexposed shot, but it won't ruin a properly exposed one.

 

[panastasia]

With experience you'll find that the 18% gray card is a good reference, and with further experience you'll find that your hand is, also. My hand gives me a zone VI +1/3 stop placement reading.

 

[RobC]

Rob, it was always my understanding that the 18% grey card WAS supposed to signify the halfway point in a five-zone range; the five zones that show detail: III-VII. Can you elaborate on your statement that you need a 0-V range for a grey card to be accurate?

See the edit I added to my previous post. i.e. yes a five stop range. That could be anywhere within your 10 zone system. 0 thru V or III thru VIII or V thru X.

 

[JBrunner]

A grey card gives you a reference for reflective metering, nothing more. It is most effective for narrow spot metering. It simply tries to represent a known quantity. When you meter some other thing and adjust for the reflectivity, you are essentially arriving at the same exposure using an extra step (an extra step that takes less time)

I just meter what I am basing the exposure on remembering that the meter is telling me the exposure that will result in middle grey, or therabouts, and then adjust the exposure to place the subject in the zone I want. After metering about, I might determine that the "correct exposure" doesn't cover the range I am photographing (ie the highlight might blow, or I wont be exposing into the shadows like I want). I will further adjust exposure for the range I need for an adjusted development and printing, to get the photograph I envision.

Variables include how you are viewing the card, the spectral response of the meter, the spectral response of the film (the card may be grey but not the subject, and black and white films have differing sensitivity to particular colors, the same luminance of red won't expose identically to the same luminance of blue), and your personal film speed (even if you don't know what it is), development and printing process.

I rarely use a grey card except to compare one meter against another, or to photograph when testing film speeds

Above all it is a reference. You could use near any shade as long as you knew how it compared to the exposure, and adjusted from there.

 

[2F/2F]

We wuz both a-edittin' at de same time. Ah gitz whut you sez now!

 

[David William White]

With all due respect to Rob, I was explaining how to use a grey card, which was the subject of the post. My comment are correct. If you do general photography with a simple SLR with center-weighted 18% meters, then metering off a grey card solves the problem of overriding the camera meter reading when shooting bright scenes or dark scenes. In lieu of a grey card, metering off your hand or off the grass often makes an acceptable reflected reading.

A great number of photographers here much prefer reflected spot metering, taking multiple readings and mapping them to zones, arriving at ONE aperture/shutter combo, work out a specific development time to best capture the scene. They have reason to believe that everything else sucks, as they are seeking total control and perfection.

I should mention that besides reflected average readings, or reflected spot readings, the other camp is the incident metering crowd. Most studio photographers prefer incident metering. You know the exposure chart stamped inside the film boxes? Those charts are based on values of incident sunlight, and are quite suitable for general purpose quality negatives.

So, back to your problem: You may be over or under-developing your film. Are you judging the quality of your exposures by doing a contact sheet? What sort of meter are you using to take a reading off your grey card?

 

[RobC]

With the greatest of respect to those who may think the following is dis-respectful, one of THE major bonuses of doing film speed and development calibration is that it irons out errors in your meter being off by say a 1/3 of a stop. (Providng you have used your meter during film speed and dev calibration). The point being that you get more accurate exposures assuming you know what you are doing. As soon as you introduce a grey card into the proceedings, you almost guarantee introducing inaccuracies. Maybe only half a stop but never the less, because no one sets a grey card accurately for expsoure readings, you introduce errors. Why do that when you could do it more accurately with a light meter alone?

It's a comfort blanket.

 

[David William White]

I agree, Rob. And thinking over our poor soul who started this, without knowing how he is equipped and what he shoots, could we agree that he should go back to basics, skip the grey cards and the spot meters, and just work on using his built-in meter and improve his negatives by recording his development time & temp, making proper contacts sheets, finding his film speed, etc?

Oh, and since he's shooting roll film, maybe he should bracket. That will also tell him about his camera meter's calibration.

 

[2F/2F]

Dude...you guys are, like, wack or something. He should just shoot digital...dude. C'mon bro...get with the times.