18% Grey Card. To use it or not.

[halfaman]

Every scene is different, and you might change your mind about 'what is most important in the scene?'.

Photo 1 was metered with a spotmeter on the 18% gray card, because 'correct exposure' of the gray card was the most important thing to get...the gray card is reproduced as a midtone.

Photo 2 was metered with evaluative metering becajse the blue sky and the clouds was an important element, and 'correct exposure' of the gray card was not essential.

Gray cards are just references, 18% gray card is what supposedly chose Ansel Adam as a reference of mid gray for the zone system and what reflected meters are usually calibrated with. In the above scene, the first picture is "correctly exposed" (= to get a mid gray) for the dark part by the reflected spot or center weight meter. If your point of interest is in the sky, the gray card should be outside in the highlight area, something that it is not possible to do in many ocassions. So the use of gray cards have a very limited utility.

Matrix or evaluative metering is reading the brightness of many areas of the whole scene and checks for the differences. Then it chooses the exposure trying to preserve as much as possible shadow and highlight detail according to the recording media (negative/slide, CCD/CMOS sensor). Here a gray card adds nothing to exposure calculation.

There was a tendency in film evaluative metering to preserve highlights in detriment of shadows because of slide film. Modern evaluative metering also takes into account the actual color, so brightness is evaluated as RGB and not as a gray value (like reflected by a gray card), and the focus point to deduct where the photographers point of interest is.

 

[Chan Tran]

Err, no.

Lets say the subject is in sunlight, but far away. A meter illuminated with the same sunlight, and pointing at the camera, will have the same reading as it will located at the subject - same sunlight, same direction. In a studio, taking an incident reading at the subject location and at the camera location isn't going to work very well.

Sorry to be belaboring an obvious point.

That's because the distance between the sun and the earth is very far so although the far away subject is quite far the percentage of difference is very small. In the studio the distance between the light and the subject is close and between the subject and the camera is a large percentage difference.

 

[runswithsizzers]

Kodak's instructions (link in post #47) illustrate the complications involved when using a gray card. The first complication is trying to estimate an angle that is 1/3 of the total angle between the subject and the primary light source. Some people have "perfect pitch" -- the ability to accurately identify certain audio frequencies. What I do not have is "perfect protractor" -- the ability to accurately visualize angles in 3D space. (Probably why I am no good with a pool cue.)

And then there are the rules for when to adjust the gray card reading.
The first adjustment rule is: "For subjects of normal reflectance, increase the indicated exposure by 1⁄2 stop." I've never really understood the rationale behind this suggestion. I assume the 1/2-stop additional exposure is necessary because 18% is not the correct reflectance to represent the average reflectance of a normal scene?

Due to the high cost of Kodak brand gray cards, I was tempted into buying some Delta brand gray cards at a much lower cost. Delta advertises the same specifications as Kodak, 18% gray, plus or minus 1%. However the Delta instructions are slightly different. Delta says the correct angle is "halfway between the main light and the camera." And Delta does not suggest adding 1/2 stop exposure to normal subjects.

I still carry a Kodak gray card, but I rarely use it. For most subjects and conditions, my built-in camera meters are adequate - if used with good judgement. If I want a second opinion in difficult lighting, then an incident meter does pretty much the same thing as a gray card, and it is less fussy to use.

 

[xkaes]

I can think of insurmountable circumstances that can render an incident meter useless, like trying to estimate the light falling on the opposite side of a canyon thousands of feet deep. You can't just hop over there, take an incident reading, and hop right back.

Sure, there are a few instances where it's impossible to get an incident meter into the same light as the subject -- a sunset is another example -- but 9 out of 10 times that's not a problem, and 9 out of ten times a reflectance meter (even a spot meter) will not be reading an 18% reflectance area. If a mountain is covered with snow, an incident meter will get it right, while a reflectance meter will give you 18% gray snow.

 

[gary mulder]

Err, no.

Lets say the subject is in sunlight, but far away. A meter illuminated with the same sunlight, and pointing at the camera, will have the same reading as it will located at the subject - same sunlight, same direction. In a studio, taking an incident reading at the subject location and at the camera location isn't going to work very well.

Sorry to be belaboring an obvious point.

There is a phenomenon what we normally refer to as aerial perspective. Objects further away have less contrast, are lighter and different in color.

 

[DREW WILEY]

Xkaes - intelligent use of a spotmeter does not factor just 18% gray, but any number of readings either side of that. And in nature, one also learns substitutes for gray cards. Gosh, it's fun to differentiate all the shades of diorite or quartz monzonite or andesite, all those granitic lovelies, just as long as one is hanging on to a little ledge with one hand while reaching for the meter with another, and hoping a yellow jacket wasp doesn't land on your nose at the same time - which actually happened to me once!

The built-in IRE scale of the Pentax digital meter can potentially be helpful for indicating the typical range of transparency films. Others assign Zone System values to the EV increments, although I've never liked those Zone labels sometimes attached to meters; they're redundant. After awhile it all gets spontaneous and second nature anyway.

After a person has botched a few exposures of snow, they start asking why. But there are all kinds of snow and amounts of reflection. That's why spot meters are so nice - you can measure the exact amount of reflection in a small area relative to other readings in the scene, rather than just guessing this or that stops of correction. You can determine if you film is even really capable of capturing the full range, and what needs to be sacrificed if it doesn't.

Regardless, I'll just repeat that what is most important is sheer familiarity with one's own metering equipment, as well as with their subject matter. And much of that comes through trial and error experience. But for serious work, a real handheld light meter can be a wise investment. It allows you to intelligently control your entire workflow, rather than consigning it to the whims of an algorithm. I don't even own any of those kinds of cameras anyway; no need.

 

[wiltw]

Gray cards are just references, 18% gray card is what supposedly chose Ansel Adam as a reference of mid gray for the zone system and what reflected meters are usually calibrated with. In the above scene, the first picture is "correctly exposed" (= to get a mid gray) for the dark part by the reflected spot or center weight meter. If your point of interest is in the sky, the gray card should be outside in the highlight area, something that it is not possible to do in many ocassions. So the use of gray cards have a very limited use.

IF the intended use is to recreate the tonal range WHERE THEY FALL INHERENTLY within the range of brightness (between white and black) the grey card permits faithful reproduction within that range.
That is a major purpose of the 18% gray card.
In digital photogaphy, one often hears about ETTR (Expose to the Right) and if one does that, 18% gray may be photographed as BRIGHTER THAN 18% gray...so during postprocessing, one can move that tonal area back to 'mid tone' and the rest of the range of brightnesses in the scene move along with it, to their INHERENT brightness levels.

There are many clients of photography who insist upon accurate tonal reproduction...for example, a clothing manufacturer wants the proper level of brightness to show up in the printed ad, so as to not mislead a potential buyer that 'light grey' item is actually a bit darker (and what they are not seeking). A gray card helps to guarantee accurate tonal reproduction of that item. As @halfaman stated, "Gray cards are just references", but they can be a very important reference point.

 

[DREW WILEY]

Gary and wilt - back to gray card quality control. I once took a huge stack of gray cards of various brands, and even within the same brand, and ran them through an expensive industrial spectrophotometer. Most were seriously off, both in terms of percent of reflectance, as well as actual neutrality of gray (important if the gray card is left in a representative frame to serve as a calibration reference). Kodak ones fade easily and are unreliable, Delta ones are all over the map, depending on the batch lot. Some cards were as much as 15% off, and not even one of them was true neutral gray.

Everyone should get ahold of a serious quality reference instead. Use a MacBeth Color Checker chart or direct equivalent.
They aren't cheap, but are worth it. Keep it clean and unfaded, and use it as a reference to measure the accuracy of your other gray cards and gray discs. That's just like how I keep a true machinist's square on hand to check all the other squares in my shop, and a true machinist's level to check my other levels before I trust them.

 

[wiltw]

Gary and wilt - back to gray card quality control. I once took a huge stack of gray cards of various brands, and even within the same brand, and ran them through an expensive industrial spectrophotometer. Most were seriously off, both in terms of percent of reflectance, as well as actual neutrality of gray (important if the gray card is left in a representative frame to serve as a calibration reference). Kodak ones fade easily and are unreliable, Delta ones are all over the map, depending on the batch lot. Some cards were as much as 15% off, and not one of them was true neutral gray.

Everyone should get ahold of a serious quality reference instead. Use a MacBeth Color Checker chart. Keep it clean and unfaded, and use it as a reference to measure the accuracy of your other gray cards and gray discs.

I do not doubt that there are some gray card production issues especially in inferior products that are offered. Buyer beware.
OTOH I have a Koday gray, a gray patch on Colorchecker, a Douglas gray card, and an Photovision target (with gray segment as well as black and white segments) and ALL read within 0.1EV with my Minolta Spotmeter, and our shutter speeds and apertures are not so precisely regulated.

On the issue of 'neutrality' of color balance, that characteristic only came about in relatively recent years. Back when Ansel was promoting the gray card, its use was entirely for tonal reproduction...black and white prints did not need to be 'color balanced' So one could understand that absolute neutrality could be lacking in many items still floating around from the 40's thru 60's, and a spectrophotmeter could detect that.

 

[xkaes]

Sorry to be belaboring an obvious point.

It's unfortunate that you can't talk people out of their very expensive spot meters -- and hours reading Zone system material. It's called "cognitive dissonance". I use a spot meter on my Minolta meter sometimes, but hardly ever. The incident meter is so much better. My only problem is deciding if I want to use the flat or dome diffuser.

Don't have an incident meter? Just stick a white styrofoam cup over your camera lens and point it toward the film. E-Z-P-Z

 

[Chan Tran]

It's unfortunate that you can't talk people out of their very expensive spot meters. I use a spot meter on my Minolta meter sometimes, but hardly ever. The incident meter is so much better. My only problem is deciding if I want to use the flat or dome diffuser.

Don't have an incident meter? Just stick a white styrofoam cup over your camera lens and point it toward the camera.

Incident meters are cheap. For $50 you can get a good used Minolta incident meter like the autometer III

 

[DREW WILEY]

Hue neutral gray cards became quite important when color negative film portraits were submitted to labs for printing. It was assumed the studio had properly balanced their lighting, which any competent studio would have done. But batches of film itself might differ, or other issues be in play. So a gray would be present in a representative frame which they could read with their color analyzer, to simplify the workflow.

Ansel knew about that too, although he didn't do much color photography himself. I'm sure his official Presidential portrait of Jimmy Carter on 20X24 Polaroid was extremely well balanced lighting-wise, and pre-tested, before he pressed the shutter. Polaroid's own staff were on hand to make sure of that.

I was primarily a color photographer and printmaker before I ever took up black and white as well. But that was mainly in reference to chrome film, which can be visually evaluated on a light box before proceeding forward.

I sometimes carry a high-quality (measured and tested) collapsible gray disc for sake of pre-flashing color film in the field. I don't do that very often; but in that case, neutrality is quite important.

 

[xkaes]

Incident meters are cheap. For $50 you can get a good used Minolta incident meter like the autometer III

You can get a lot of good incident meters for much less. There are, for example, nice, simple, Vivitar meters with incident metering for $10 -- and others as well.

I don't like the digital meters, so I have not "up-graded". I like a meter that displays ALL of the f-stop and speed combinations at the same time.

 

[wiltw]

It's unfortunate that you can't talk people out of their very expensive spot meters -- and hours reading Zone system material. It's called "cognitive dissonance". I use a spot meter on my Minolta meter sometimes, but hardly ever. The incident meter is so much better. My only problem is deciding if I want to use the flat or dome diffuser.

Don't have an incident meter? Just stick a white styrofoam cup over your camera lens and point it toward the film. E-Z-P-Z

Indeed, I find for most shooting the incident meter is what I pull out. When I pull out my Minolta Spotmeter is mostly for studio, shooting products, when I carefully read local brightnesses within the scene to ensure that the illumination all falls with a narrower 7EV range in order to best fit within the narrow dynamic range of offset printing press.

On the topic of flat disk vs. hemisphere...

• 3D scene - hemisphere (aimed at lens)
• 2D flat art - flat disk
• light source intensity ratios (for portraiture contrast control purposes) - flat disk aimed at individual sources
• portraiture exposure - (see 3D scene)
• localized lighting - spotmeter

fairly simple

In this shot, done during a product photography workshop exercise, incident meter was used for overall exposure, spotmeter was used to determine wine glass transillumination and spotmeter was used for transillumination lighting on background, and spotmeter was used for light range control (highlight vs. shadow zones)

 

[cowanw]

Don't have an incident meter? Just stick a white styrofoam cup over your camera lens and point it toward the film. E-Z-P-Z

Aaawk, you will need a really good bellows to do that, if the film is in the camera.

 

[Bill Burk]

I carry a gray card in my wallet and use it about as often as those Ace rewards cards. Not often but when I want a gray reference it’s there. Right next to one of those funky folding phone “tripods” my brother in law gave me.

 

[Chan Tran]

You can get a lot of good incident meters for much less. There are, for example, nice, simple, Vivitar meters with incident metering for $10 -- and others as well.

I don't like the digital meters, so I have not "up-graded". I like a meter that displays ALL of the f-stop and speed combinations at the same time.

I have the Minolta Autometer II for that but I found that often I only read the EV number.

 

[xkaes]

I have the Minolta Autometer II for that but I found that often I only read the EV number.

Me too. The Autometer II is great because it has the motorized dial that rotates the scales on its own.

 

[Alan Edward Klein]

Not always necessary.
It isn't uncommon to have one side of a river be in exactly the same light as the other.
You have to observe carefully in order to check for differences, but you can often do that check reliably just by looking at the scene.

My post says studio light.

 

[Chan Tran]

Me too. The Autometer II is great because it has the motorized dial that rotates the scales on its own.

The Autometer and Autometer II with the motorized dial and thus their name. The newer Autometer III thru 5 just keep the name.

 

[xkaes]

The Autometer and Autometer II with the motorized dial and thus their name. The newer Autometer III thru 5 just keep the name.

The Auto Meter II uses the body of the Auto Meter Professional, but makes some major improvements. Most importantly, the Auto Meter II uses a silicon cell. While this only increases the sensitivity a little, it makes the meter easier to use. The low/high scales are gone, and the Incident-Reflectance switch is moved to the front. The screw-in attachments are replaced with bayonet attachments. The meter has a lock to prevent accidental operation, but the use of the meter is the same as its predecessor. The 5° attachment was not designed for this meter, but it will fit and work -- with a 4X ISO adjustment. With its low-light capabilities (the best of any Minolta meter) and motorized control, the Auto Meter II can't be beat -- unless you need flash, spot, or color temperature readings. This was Minolta's last meter to offer a full-scale display where all of the f-stop/shutter speed combinations are displayed at once. After this, you need to spend time picking a shutter speed on the meter, and then the meter will indicate the f-stop. So much for "progress"! You want the most sensitive and easiest to use meter? This is the one to get. Accessories included a close-up probe, enlarger mask, flat diffuser, 10 degree spot attachment, spherical diffuser, 4X neutral density diffuser, 8X neutral density diffuser, case for meter, and neck strap.

 

[DREW WILEY]

Sounds a bit bulky for a backpack. I had the Minolta Spotmeter F, which was nice and compact; but I found the pushbutton controls less intuitive than the manual rim dial on the Pentax digital spotmeter.

 

[BrianShaw]

Kodak's instructions (link in post #47) ...

And then there are the rules for when to adjust the gray card reading.
The first adjustment rule is: "For subjects of normal reflectance, increase the indicated exposure by 1⁄2 stop." I've never really understood the rationale behind this suggestion. I assume the 1/2-stop additional exposure is necessary because 18% is not the correct reflectance to represent the average reflectance of a normal scene?

Quite possibly because meters, if conforming to the ANSI/ISO standard, are calibrated to a specific luminance value that approximately represents 12% gray...

 

[Chan Tran]

Sounds a bit bulky for a backpack. I had the Minolta Spotmeter F, which was nice and compact; but I found the pushbutton controls less intuitive than the manual rim dial on the Pentax digital spotmeter.

That is why I suggest someone just make the dial and sell it. Both the Pentax and the Minolta display the EV number in the viewfinder. You would then set this number on the dial so you can have a separate dial to do the same thing.

 

[Chan Tran]

Quite possibly because meters, if conforming to the ANSI/ISO standard, are calibrated to a specific luminance value that is approximately 12% gray...

No but because for very dark subject when metering as is would put it too close to the toe which starts to lose details and contrast. Adding a 1/2 stop bring it up into the curve where the curve is more straight and because the subject is all dark there is no danger of burning out highlight. I face fi the subject is all black you may want to put in at the center of the curve then print it darker.