Downloadable 18% Gray Card

A kodak 18% grey is the middle of what exactly? When you can fully explain that and can quote the angles it requires and can implement those angles before metering it, then you will realise that a grey card is as much use as a concrete parachute and do what all sensible people do and throw it away.

Robint said:

To throw a spanner (wrench) in the works, I read an article that camera's are calibrated at 12% gray.

http://www.bythom.com/graycards.htm

Comments

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That 12% is what is called a K factor and its what camera and meter manufacturers use to calibrate their meter to the mid point of the film characteristic curve. That begs a few questions such as which film?
For example, a colour neg film or chrome/transparency film. There is abig difference between them.
I don't know what the K factor for my contax camera is but I have heard many times that the in camera meter is calibrated for transparency films. But then not all transparency films have the same dynamic range. And nor do all negative films. That is one of the major reasons why you should do your own film testing and exposure calibration.
My minolta spot Meter F uses a K factor of 14. Not that that is really worth knowing because again, the particular film dictates what the exposure should be and not the meter. So calibration is required.

You ought to be able to make one in MSPaint. Custom colors, pick a neutral and adjust it to the midpoint of 255 and 0 (127) and fill a frame and then print it.

rob champagne said:

A kodak 18% grey is the middle of what exactly?

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The value of "18%" was/ has been selected as an ARBITRARY determination of "mid-color" and density of the "average" scene. By whom and just what the parameters of selection were, I have no idea, and I wonder if anyone else does.
"Precise and/ or exact"? I doubt it - more like "better than nothing".

When you can fully explain that and can quote the angles it requires and can implement those angles before metering it, then you will realise that a grey card is as much use as a concrete parachute and do what all sensible people do and throw it away.

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What is with this "angles" business? In use one substitutes the gray card for part of the subject, in the same light, and the exposure is set. Then if 95% of the light is reflected from a white subject surface, it will be recorded as 95% white, not 18% gray. The meter itself doe not know whether the subject is supposed to reflect 5%, 18%, 95% or whatever - it will process the information to produce 18% gray (or 12% - or 13.5% - I don't think there is a great deal of difference)..

A "concrete parachute?" Certainly not perfect - but as stated before, a whole lot better than nothing.

Ed Sukach said:

What is with this "angles" business? In use one substitutes the gray card for part of the subject, in the same light, and the exposure is set.

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Ever bothered to read the instructions that come with a genuine kodak grey card? Obviously not. here's the relevant paragraph:

“Position the grey card in front of and as close to the subject as possible. Aim the surface of the gray card toward a point one third of the compound angle between your camera and the main light. For example, if the main light is located 30 degrees to the side and 45 degrees up from the camera to subject axis, aim the card 10 degrees to the side and 15 degrees up.”

This means you need to buy a sextant to use a grey card accurately.
Don't take my word for it. Just point a light meter at a grey card or any card for that matter, and change its angle around and watch your light meter change its reading. And see its apparent colour change depending on its angle.

So what's the point of a grey card. You have no idea what percentage or colour it is unless its set perfectly accurately and even then who says 18% is the mid point of your subject? I bet it isn't.

Of course if you always point it at the camera then at least its consistently wrong and no doubt you have calibrated your methods to take that into consideration without even realising.[edit]And unless the lighting direction is always exactly the same then it's NOT a consistent reference is it.[/edit]

Why not just take a light reading of the actual light falling on the subject and tear your grey card up. It's simply making things more inaccurate and patently not required when you have a light meter to do the job for you. And AA said himself that if the whole subject is not in the same light, then a grey card is useless. Since anything in shadow is not in the same light as the rest of the image, then that accounts for about 99.9999999% of all images which AA said a grey card is not suitable for. You will have to read the Negative properly next time so that you don't miss that "Very Important" sentence.
[edit]Just point your incident meter directly at the light source which is illuminating what is facing the camera and you will get highly accurate and consistent light readings. The tones rendered will fall where they fall but if you are consistent with your metering then you will know very quickly whether to adjust exposure or development from the reading[/edit]

Rant over. Normal service resumed... Oh that was normal. Well never mind.

rob champagne said:

]Just point your incident meter directly at the light source which is illuminating what is facing the camera and you will get highly accurate and consistent light readings.

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Actually, a typical domed incident meter is supposed to be aimed at the camera lens from the subject position, or in that same orientation in the same light as the subject, not directly at the light source (unless it's on the same vector as the camera). The meter dome can then account to some degree for the shadows created by the sun as seen from the camera, giving a bit more exposure when there is more in shadow. An extreme case of this would be with backlighting 180 degrees from the lens. You typically want to meter the side of the subject seen by your camera, not what's lit directly by the light source, i.e. the part of your subject turned away from the camera when backlit.

I expect you know this, and only commented because there are a lot of people new to this who might not make the distinction.

Lee

No sextant, I prefer an astrolobe....

rob champagne said:

“Position the grey card in front of and as close to the subject as possible. Aim the surface of the gray card toward a point one third of the compound angle between your camera and the main light. For example, if the main light is located 30 degrees to the side and 45 degrees up from the camera to subject axis, aim the card 10 degrees to the side and 15 degrees up.”

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That's why the high reflectivity of the Delta card bothered me. Hold it just a bit different and the reflection changed, and hence, the metering.

It's been so many years since I owned a Kodak card I can't recall the surface.

I guess I'd forgotten those instruction, maybe intentionally. I typically just hold it vertically and facing the light or lights. Camera position, up to maybe a 45 degree off centerline position, would "reflect" the decreasing light, for instance.

Anyway, if it is sunny outside, I use sunny sixteen, close a third of a stop (i.e., pretend ISO 100 is 125) and damn.....it always works!

rob champagne said:

Ever bothered to read the instructions that come with a genuine kodak grey card? Obviously not.

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One thing that burns my socks is someone who expects to prove a point by asking and answering their own question. That was YOUR answer - this is mine:
Yes, I HAVE read the instructions accompanying the Kodak Gray Card... and I did not understand them either. Blundering along in my own way, I STILL found that the use of the card did have value - in certain circumstances, exposure and color balance was closer - much closer to "ideal". It may be of interest to you that I found the Kodak GC to be more unstable, especially when left in light and questionable ambient conditions, than the more substantial Delta.

here's the relevant paragraph:
“Position the grey card...
This means you need to buy a sextant to use a grey card accurately.

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Obviously, you have never used a sextant. Not suited for setting angles like this.

Don't take my word for it. Just point a light meter at a grey card or any card for that matter, and change its angle around and watch your light meter change its reading.

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True. It will. And the reason you WANT to change the angle - and get various readings is ... why? I'll leave mine at 90 degrees to the optical axis of the lens, and go from there.

And see its apparent colour change depending on its angle.

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No. The APPARENT color - in MY perception of it - stays the same.

So what's the point of a grey card. You have no idea what percentage or colour it is unless its set perfectly accurately and even then who says 18% is the mid point of your subject? I bet it isn't.

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No bet. I doubt that it is exactly 18% either - but - please re-read what I wrote - "CLOSER than nothing".

Of course if you always point it at the camera then at least its consistently wrong and no doubt you have calibrated your methods to take that into consideration without even realising.

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"Wrong" or "right', the fact that it is CONSISTENT is what matters.

....And unless the lighting direction is always exactly the same then it's NOT a consistent reference is it.

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???? When the light changes ... intensity, direction, color ... one is obliged to take another measurement. is this different with reflective metering?.

Why not just take a light reading of the actual light falling on the subject and tear your grey card up. It's simply making things more inaccurate and patently not required when you have a light meter to do the job for you.

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Try, "Because I damned well want to." From experience I get MUCH better results by eliminating the effects of subject reflectivity, and a very useful starting point for color balance. Nine tiimes out of ten I will use incident metering (no gray card), but at that tenth time an exposure of a gray card is *VERY* useful.

And AA said himself that if the whole subject is not in the same light, then a grey card is useless. Since anything in shadow is not in the same light as the rest of the image, then that accounts for about 99.9999999% of all images which AA said a grey card is not suitable for.

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UH ... I hate to bring the news to you, but most of Adams work was unsuitable for use with a gray card. One would need a very large card to replace a significant portion of "Storm Clearing Over Yellowstone". Incidence metering would not be suitable either.

You will have to read the Negative properly next time so that you don't miss that "Very Important" sentence.

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I ... I ...
... No I refuse to let you bait me with this.
Considering what has been written here, I think our individual "reading efficiencies" have already been established.

so you can't see that the grey of the card becomes lighter or darker depending on the angle of the card? Wow.

For what it's worth 18% reflectance is always approx 2 1/2 stops less than 100% reflectance. That's important because if you have a film such as chrome, which are high contrast films and have a useable range of maybe 5 possibly 6 stops then 18% is around the mid point of those films. If you are using colour negative films which have a scale of maybe 7 or 8 stops, the 18% reflectance is not the mid point and if you have calibrated your black and white film for a 10 zone system, then 18% reflectance is around zone 7 1/2. NOT V as AA said. He must have been wrong and knowone noticed.

That's going to confuse a lot of people but the maths to prove it is incredibly simple. One stop brighter than 18% would be 36% reflectance. And one stop brighter again would be 72% reflectance. An one stop brighter again would be 144% reflectance. But that's impossible. So approx 2 1/2 stops brighter is 100% reflectance. Or to put it another way, if you metered the brightest part of your subject, then anything 2 1/2 stops less bright in your subject, would be 18% of the brightest part of your subject and if you placed your grey card at that point ( at the correct angles) it should give the same reading.

If as an extreme example, we had a 20 stop SBR, 18% would still be 2 1/2 stops less than zone 20. So you should be able to see that 18% is only the mid point of a 5 stop range. That's suited to chromes and NOT black and white film, especially when you are using a 10 zone system.

So is a kodak grey card a known reference which many seem to think it is?
Well yes it is. BUT, only if you know exactly the useable range of your film and where 18% falls in that range and only if it is set to absolutely the correct angles to make it reflect 18%. How many people can say they can achieve that?

What I find so irrational is that, the only known reference you have, assuming it is working properly, is your light meter. People trust their meter to meter from a grey card but they won't trust the meter to meter directly from the light source. Same meter but metering from two different things. One is not trusted. The other is. It's as if they believe the grey card has magic properties and any light that touches it must be magically converted to being
a correct exposure even though it's damn near impossible to meter from a grey card and retain a known reference which is why people claim they use it.

The light meter on the other hand is still working perfectly and gives consistent readings. And then to cap it all, when they don't have a grey card, they still don't trust to point the meter at the light source because they are worried about the shadows, so they point it at some indeterminate point bewteen the light and the camera. It's no wonder they get unreliable readings.

rob champagne said:

so you can't see that the grey of the card becomes lighter or darker depending on the angle of the card? Wow.

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Another example of mis-reading. I did NOT say there was no change in the amount of light reflected - I DID say that I perceived *NO* change in COLOR. Double WOW!

For what it's worth 18% reflectance is always ...

The light meter on the other hand is still working...

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In another life, I was involved in the calibration and operation of photometers - Cascade Photomultipliers - and such; and many attempts to use various run-of-the-mill" photographic exposure meters in industrial and laboratory applications *far beyond their capabilities. Your description was fun - all the way back to "Measuring Light 101"'.

... And then to cap it all, when they don't have a grey card, they still don't trust to point the meter at the light source because they are worried about the shadows, so they point it at some indeterminate point bewteen the light and the camera. It's no wonder they get unreliable readings.

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Who are "they"? All those that use gray cards? Isn't it possible that some, through sheer luck, or extensive experience, actually obtain useful information from their use?

You have been bouncing between reflective and incident metering. Reflective meters always assume that the metered area is 18% gray (one exception - the internal meter of the Olympus Om4 series - switchable from 5%, 18% and 95%) whether it is a snowbank, coal mine or "average" scene and will give a exposure value appropriate to an 18% reflectance. Using a gray card, that built-in assumption is more or less, correct - and it is possible - imperfectly possible - to acheive an acceptable exposure.

Incidence metering does NOT carry this 18% "assumption". However, all meters - especially the built-in ones and "spot" meters do not have the capapbilty of incidence metering and gray cards are a fairly decent accessory.

I have a feeling a relative of Mike Scarpitti has arrived.

C

I don't think so. I've visited his site and he has some *VERY FINE*(!!) work there, unlike another whose name is never to be written here.

I disagree with what he is saying. I've disagreed before, with others as well, but I do not intend those disagreements to morph to a attack on his, or anyone else's, character.

Newbie here, here

CBG said:

I have a feeling a relative of Mike Scarpitti has arrived.

C

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Dare I ask? Or should the stake remain in the corpse?

On another note ... what does the collective intelligentsia think of this ...?

Take a photograph of a gray card in color. Develop and print the image. Take the result and compare it with the original gray card, side by side, with a scanner, or more accurately, a reflective color densitometer (or, if you want to get dizzy, by eye).

I think that, if there is very little difference - the process, the exposure and color balance in printing, considering the lighting ... sundry other factors ... all MUST be pretty close to what it should be. If the two vary, at the very least, there should be a fairly reliable indication of what direction to follow.

Comments?