What Gray Card?

Thomas71 said:

Here in Italy a well-known b&w teacher states that incidental reading leads to systematic underexposure and that the greater the contrast in the scene, the greater the level of underexposure. I honestly have not yet understood the reasons for this and use incidental reading when I can.

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I have never had that problem. When I took photographs while skiing I used the light reading off my palm and closed down a stop or used an incident meter. The incident meter did not underexpose, it exposed correctly. That teacher needs to have his incident meter calibrated rather than complain that his problem is a problem for everyone else.

While I use my own system and occasionally a gray card or incident meter I thought I would follow up on the Home Depot challenge and emailed Behr asking if they had an 18% gray and how they determined it. They answered promptly and asked me to scan the gray card and give them the RGB information. I scanned it and sent a screenshot of the card and PhotoShop numbers. They again answered with what they felt matched I went to HD and bought a sample for $6.50 and will paint a couple of different surfaces. I will compare to my never used pristine gray card. I will keep all posted.

jeffreyg said:

While I use my own system and occasionally a gray card or incident meter I thought I would follow up on the Home Depot challenge and emailed Behr asking if they had an 18% gray and how they determined it. They answered promptly and asked me to scan the gray card and give them the RGB information. I scanned it and sent a screenshot of the card and PhotoShop numbers. They again answered with what they felt matched I went to HD and bought a sample for $6.50 and will paint a couple of different surfaces. I will compare to my never used pristine gray card. I will keep all posted.

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Please keep us informed and follow up.

Thomas71 said:

Here in Italy a well-known b&w teacher states that incidental reading leads to systematic underexposure and that the greater the contrast in the scene, the greater the level of underexposure. I honestly have not yet understood the reasons for this and use incidental reading when I can.

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I have never had issue with incident meter yielding inaccurate exposure, either. In fact, if you shoot digital camera with incident meter reading it gives an exposure with midtone positioned right in the center of the histogram, and the white and black panels of my EZ Balance target flanking...see the histogram to the right portion of my second image (EZ Balance target) in my post 173. The 'midtone' would be positioned to the left of center of the histogram, if incident meter gave the wrong suggested exposure. (BTW that EZ Balance target black panel and white panel meters -2.1EV and +2.3EV different from midtone, a not particulary 'high contrast' range)
Hard to understand why that teacher came to his/her conclusion, apart from Sirius Glass' suggestion that the teacher's meter needs calibration.

jeffreyg said:

Home Depot challenge and emailed Behr asking if they had an 18% gray and how they determined it. They answered promptly and asked me to scan the gray card and give them the RGB information

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Home Depot & Co. have scanners - you bring them a chip of the paint you want matched and the scanner comes up with 2 units of purple, 5 of yellow, 1 of cyan, 8 of medium grey ... my experience with my house and my deck is that the match is perfect (well as perfect as you expect for house & deck paint - but I can't see where the join is between the new paint and the old.) They have a large gamut of pigments to choose from.

I would bring them a Kodak card and see what they produce.

Color matching is hard - colors that match under daylight won't match under fluorescent/LED or, especially, street lights.

Sirius Glass said:

I have never had that problem. When I took photographs while skiing I used the light reading off my palm and closed down a stop or used an incident meter. The incident meter did not underexpose, it exposed correctly. That teacher needs to have his incident meter calibrated rather than complain that his problem is a problem for everyone else.

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No, I don't think that his meter need to be calibrated.
In an italian Forum many agree with the concept that in high contrast scene the incident measure leads to underexposure. They claim that it is explained in A.A."The Negative" and it seems to be explained like this:

If there is little contrast and you measure the middle everything comes in and fits comfortably...... but if the contrast is high the extremes move apart and if you measure the middle you will have the bottom underexposed and the top usually overdeveloped. With high contrast if you measure down you will save the shadows and compensate for the highlights by reducing the development time. The medium tone remains medium. When the contrast increases the shadows darken and the light tones lighten, and the medium tone remains medium. This leads to increasing underexposure as the contrast increases if the medium tone is exposed.


It doesn't matter if the midtone is measured as reflected light from a cardboard at 18% or in incident light, the (wrong) thinking is the same and the result is also the same by definition (subject to measurement errors and calibration differences).

Thomas71 said:

Here in Italy a well-known b&w teacher states that incidental reading leads to systematic underexposure and that the greater the contrast in the scene, the greater the level of underexposure. I honestly have not yet understood the reasons for this and use incidental reading when I can.

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Fascinating. Can you mention their name or send some of their course notes?

Davis, in BTZS, recommends an incident reading in the shade and then one stop down. This “bases” the exposure on shadow and the one “stop down” assigns the shadow reading to its proper shadow placement.

A full-main light reading with no adjustment might be underexposure in this scenario.

And yes… the shadow and main light disagree more and more as the contrast between them increases.

I hope that helps you see what your teacher was saying.

jeffreyg said:

While I use my own system and occasionally a gray card or incident meter I thought I would follow up on the Home Depot challenge and emailed Behr asking if they had an 18% gray and how they determined it. They answered promptly and asked me to scan the gray card and give them the RGB information. I scanned it and sent a screenshot of the card and PhotoShop numbers. They again answered with what they felt matched I went to HD and bought a sample for $6.50 and will paint a couple of different surfaces. I will compare to my never used pristine gray card. I will keep all posted.

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Bravo!

Breadbutter said:

Just in case someone is still looking for gray cards. Freestyle Photographic Supplies has 18% Delta gray cards in stock.

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I have used the Delta cards, and they are OKish, but I think I prefer the Kodak cards. For one thing the Delta cards have a lot of text on the back side, so not as versatile as the white side of the Kodak card. Sometimes I like to use the white side of the card as a reflector to provide fill light for closeup shots. I haven't actually tried to measure it, but I think the Delta cards *may* have a bit more surface sheen(?)

jeffreyg said:

And since the original post was looking for a cheap gray card

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Actually, I was more concerned about availability than cost. I was looking for either a Kodak brand card, or something at least as good. The Kodak cards are not particularly cheap, but if it's something I can trust to be consistent, the price is acceptable to me.

But I'm over it now. I have one of those gray fabric targets that coil up for easier carrying, and I think it will probably be OK for my purposes. For metering, I will continue to use my Sekonic and Gossen meters, mostly in incident mode. About the only thing I wanted the gray card for was an occasional reference point on the negative.

DREW WILEY said:

[...]
Breadbuttger - Delta cards, actually plastic, are all over the map one to another, depending on specific batch. So so at best.

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Are we talking about the same thing? The Delta brand gray cards I have used in the past were some kind of heavy paper-based stock, very similar to the Kodak cards, except with text printed on the back side, where the Kodak cards were plain white.

Color Cue says an old Kodak Dataguide gray card is 25% PANTONE Black

75% Transparent White

L*a*b* 47.33, 2.22, 6.34

XYZ 16.06, 16.27, 11.22

Or PANTONE 404C

Thomas71 said:

Here in Italy a well-known b&w teacher states that incidental reading leads to systematic underexposure and that the greater the contrast in the scene, the greater the level of underexposure. I honestly have not yet understood the reasons for this and use incidental reading when I can.

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Both reflected and incident meters assume an average scene luminance range. With shorter than average luminance ranges, the shadows don't reach as far down on the curve and with longer than average, they can fall below the minimum useful gradient level for a quality reproduction. With a reflected exposure meter, it's possible to determine the range between the meter's exposure point and the shadow. It takes more effort with an incident meter, especially if only a single reading is taken. Black and white film's quality is greatly determined by shadow reproduction. While film speed is determined by the shadow region, exposure meters also accommodate other film types like reversal which is more concerned with holding the highlights and reproducing the mid-tones. The relationship of the metered exposure point to the shadows in a black and white exposure is generally assumed.

From D. Connelly's Calibration Levels of Films and Exposure Devices, The Journal of Photographic Science, Vol. 16, 1968.

"The essential characteristic of a photograph is that it portrays a differing pattern of luminance comprising the object being photographed, but equation 3 which it is intended to use in assessing the exposure required for this range of luminance uses a single value of luminance Lg. The validity of the exposure determination method must, therefore, depend upon the acceptability of the resulting photographs which are produced by substituting a single value of luminance in the determination of exposure to represent the mulitplicity of values of luminance of the scene itself.

In practice exposure determination by this substitution is satisfactory only for what may be termed average scenes. Unusual distributions of luminance require special exposure assessment. (Emphasis mine)

From the point of view of the film, satisfactory photography depends upon the proper location on its exposure density characteristic of the densities produced by the image illumination within the camera. The greatest and least significant luminances in the scene are required to cause exposure of the film within the usable part of its exposure density characteristic. This implies that the important characteristics of the luminance are:

(i) the ratio of its maximum to its minimum value.
(ii) its absolute value (of maximum or minimum)

The former determines whether or not the film can reproduce the contrast range of the scene and the latter determines the exposure time necessary to provide an exposure which will locate the brightness scale of the scene correctly relative to the film characteristic."

So for the B&W instructor, the old adage applies, "you need to be smarter than the meter."

Equation 3

Then there were those who said Kodak cards had a 12% standard, not 18%. Old Dataguides had approximations in them, nothing critically accurate. Delta - all over the map too, whether the old printed ones or newer plastic ones. Just one more reason to buy something reliable instead, or at least compare the so-called gray cards you do have to a high quality standard like the central gray patch on a MacBeth Color Checker chart.

And Nicholas - Cheapo Depot doesn't have serious paint color duplication devices, much less people trained in properly using them. They mainly feature those devices as a placebo, trying to hoodwink people into thinking if the machine calls it a match, it is. They're not going to install high-end versions of that technology or it would get stolen by staff. Nobody with the necessary skills works in a place like that anyway. They wouldn't even understand what a proper kind of evaluation lighting consists of. Even the pigments involved are second rate and incapable of achieving a true neutral gray. That's not how it's done.

DREW WILEY said:

Then there were those who said Kodak cards had a 12% standard, not 18%. Old Dataguides had approximations in them, nothing critically accurate. Delta - all over the map too, whether the old printed ones or newer plastic ones. Just one more reason to buy something reliable instead, or at least compare the so-called gray cards you do have to a high quality standard like the central gray patch on a MacBeth Color Checker chart.

And Nicholas - Cheapo Depot doesn't have serious paint color duplication devices, much less people trained in properly using them. They mainly feature those devices as a placebo, trying to hoodwink people into thinking if the machine calls it a match, it is. They're not going to install high-end versions of that technology or it would get stolen by staff. Nobody with the necessary skills works in a place like that anyway. They wouldn't even understand what a proper kind of evaluation lighting consists of. Even the pigments involved are second rate and incapable of achieving a true neutral gray. That's not how it's done.

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The ratio of the constants K to C approximates the average scene reflectance, which equals about 12% and why the instructions with the Kodak gray card recommend opening 1/2 stop from the reading made from the 18% gray card.

Stephen Benskin said:

The ratio of the constants K to C approximates the average scene reflectance, which equals about 12% and why the instructions with the Kodak gray card recommend opening 1/2 stop from the reading made from the 18% gray card.

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And I have been walked through the math and the concept of the meter calibration constants by Ctein decades ago, and was persuaded to the veracity of the concept. Yet one cannot fully resolve this fundamental observation against what the Kodak recommendation is, just compared at 3:45pm PDT in bright sun

• Minolta Spotmeter F aimed at a geniune Kodak gray card (with no surface reflectivity to bias the reading) reads ISO 250 1/250 f/16 +0.1EV
• Minolta Autometer Vf incident meter reads ISO 250 1/250 /16 +0.1EV

I got a couple of Emails from him a day or two ago; he's gone digi. Makes no difference. "Sunny 16" ... what latitude, what time of year, what altitude? Did Krakatoa or Mt Pinatubo recently explode? Kodak gray card - which one, and how faded is it? And I leave meter calibration to the same pros who do it for Hollywood cinematographers. My calibration provider retired; but every time I got a meter back recalibrated, it precisely matched all the other ones I used, clear across the scale.

runswithsizzers said:

I just checked USA resellers Amazon, B&H, & Adorama, and the Kodak 18% gray card is not in stock. Some sellers say the Kodak gray card is "out of print" or "no longer available." This Kodak <website> describes a gray card under the heading "Motion Picture" but does not say where to get one.

There are several companies offering similar gray cards, but they are brands I never heard of. What have members tried using as substitutes for the Kodak gray card -- and which ones would you recommend to use, or stay away from?

Are the collapsable ones (printed on fabric) reasonable aternatives?

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runswithsizzers said:

Wow! Thanks for that!

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In 1995 at the annual meeting of the Biological Photographers Association in Philadelphia, Dr Martin Scot (head of Scientific imaging indicated that for 35mm Kodachrome to take a reading off the white side of the "grey card and open up 3+1/3 of a stop.
Since 'Grey cards are no longer available, I use a scrap piece of UNBLEACHED white towel (in the same 'light' as the main subject and 'open up 3+1/3 of a stop.
I have been using that 'method' ever since and will no longer use my incident meter since that piece if white toweling is easier and less 'weight/mass' to humph around when I'm out making exposures with either my 4x5 Linhoff or much older Burke and James 8x10.

Before I am accused of being classified as an"idiot". might I suggest you give it a try (at least one or two exposures'
Pretty Please????

Ken

Behr precisely matched the grey card from the PhotoShop RGB info from my scan. The numbers however were not equal more B than R and G. Somewhere I found the RGB values for the Macbeth gray card. I’ll make a print of a card using those numbers and see what comes out

Wouldn't surface reflections of the gray card materials effect readings?