Grey cards

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Guys,

Common consensus seems to be on using a grey card. Place it in the same light as the subject, tilt it so that there's no glare. And use this reading for your meter (if taking an average scene).

Now reading on the net, it seems that the average scene is not 18% but 12 %. So you should take the reading and then open up half a stop.

Which do you use? And any comments?

THanks,

-- bubble (bubblegrass@yahoo.com), June 07, 2002

Answers

18% grey is a printing, not a photo convention (the 18% refers, of course, not to the color strictly speaking, but to the reflectance factor for wite lite). meters are calibrated to about 12% reflectance. to achieve this with a typical (18%) grey card, you need to hold the card at an angle (45 degrees or so) to the meter cell. another benefit of this approach, is that you avoid (depending on the surface texture of the card) specular hilites that mite thro off the reading. the best thing in any event is to run your own density tests with your preferred film and meter to make sure you understand what is happening.

-- roger michel (michel@tcn.org), June 07, 2002.

Are you trying to start a fight? (lol) (Few topics initiate more empassioned arguments than metering technique.) Nonetheless, here are my thoughts on the matter.

In general terms, the reading provided by a reflective meter must be interpreted in some way, as the reflective reading provides the exposure to render an object of that reflectance as a medium gray (usually considered to be a Zone V in the Zone System). Using a clean, new gray card removes the need to interpret the reflective reading off some part of the subject, and should give you the same reading as a properly-used incident meter would. Whether to open up a half-stop (or even a full stop) is a matter of individual technique, which may or may not be compensated for by some other element in the individual photographer's process.

Using an incident meter (or a reflected reading off a gray card) should give you the "true tonality" of the subject, either in B&W or color, assuming tests have been run to arrive at a "working" ISO rating for the film and equipment being used. Some photographers, however, prefer to "blow out" skin tones to some degree, and will open up from the metered reading by a stop or so, depending on what they want to achieve in the final image. Thus, such statements should be filtered by differentiating between the photographer's style and the underlying metering science.

Personally, I seldom use a gray card, preferring to use either incident metering, or a spot reading and interpretive Zone placement combined with "normal" development. If using the meter in my M6TTL, I consider what the meter is reading, and adjust the exposure accordingly - aiming for an "average" exposure that will produce a printable, but not necessarily precisely exposed, negative.

Bottom line, it is best (I think) to develop a metering technique that works for you individually, and consistently apply that technique. Consistency in technique, whatever the technique, leads to consistency in results.

-- Ralph Barker (rbarker@pacbell.net), June 07, 2002.


Incident Light meter... I gave up on gray cards after losing every single one of them and some of them showed up in my PHOTOS! The NERVE! 8-)

Now I carry a Seckonic Studio Deluxe incident meter in my pocket when I doubt the voracity of my built in meter. No batteries, small and quick.

-- Bob (bobflores@attbi.com), June 07, 2002.


I don't think too much could be added that would improve on Ralph's response. I think he's provided you with some really good information. Some photographers develope their own, often strange or seemingly convoluted, metering "techniques". In one of the Ansel Adams (series) books, probably THE NEGATIVE, Adams describes (hilariously, to my mind) Edward Weston's metering technique! - interesting reading! But we all know how effective it was!!! What works best for one, is what works best for one!

Regards,

-- Art Waldschmidt (afwaldschmidt@yahoo.com), June 07, 2002.


ralph -- i agree with your conclusion (and i must add that i have never used a grey card for actual picture taking purposes). however, if you are suggesting that meters are not calibrated to an absolute standard, you are wrong. point the meter at a pure white wall and take a picture with no compensation and you will see (assuming you have done the density tests necessary to work out your film regimen -- and again there is an absolute standard for iso) the shade of grey to which the meer has been calibrated.

-- roger michel (michel@tcn.org), June 07, 2002.


I fully agree with Roger here.

As for incident metering, this method only works well when the subject is near enough (or the lighting of it can be appreciated as exactly similar to a reachable point). Besides it only gives you the htoretical exposure without any direct nterpretative capabilities.

Though the gray card is useful in reproduction work when reflected metering is the only possible solution (some incident meters have a flat adaptor to convert them to a luxmeter which is an enven more convenient solution here).

Friendly.

François P. WEILL

-- François P. WEILL (frpawe@wanadoo.fr), June 07, 2002.


Alongside metering, a grey card is also useful for getting a good colour balance in scans.

I use a grey card with additional painted-on black and white squares. When taking (architectural) photos I include the card in the shot in an inconspicuous area. That way when I come to do the scans I can use the black + white + grey as colour targets for adjusting the colour balance.

This is a god-send for mixed lighting work! When you've finished using the card you just rubber-stamp it away.

-- Andrew Nemeth (azn@nemeng.com), June 07, 2002.


Francois,

If one is going to use a gray card, then wouldn't you, by definition be close enough to use an incedent meter?

-- Bob (bobflores@attbi.com), June 07, 2002.


Roger - I'm not sure where you got the idea that I was suggesting that meters aren't calibrated to an absolute standard, but I wasn't. So, I think we're in agreement.

In contrast, the "calibration" of the photographers using those well-calibrated meters appears to vary widely. Hence, all of the arguments over "correct" technique, I suspect. ;-)

Of course, the applicability of ISO standards to real-world shooting conditions might be questioned. But, that's a different discussion. ;-)

-- Ralph Barker (rbarker@pacbell.net), June 07, 2002.


Not to offend anyone here, but the incident meter is great in the studio where things are controlled, but in real life it is a lazy mans way of exposure calculation. I use a spot meter. I use a grey card [calibrated] for some macrowork. I do use a color strip [included in the photo] to standardize color balance in many photos. 6 x 6 is good for that. Hey, I don't do this for a living, so I could be wrong.

Art

-- Art (AKarr90975@aol.com), June 07, 2002.



In the Nikon School 30 years ago they told us to use one's palm of the hand; and then adjust one stop...The teachers were one black and one white guy; their meter readings from their two different palms were very close..............This was used in case one didnt have an 18% card handy; and had at least one palm..........

-- Kelly Flanigan (zorki3c@netscape.net), June 07, 2002.

ralph -- in rereading your post in lite of your comments, i realize i misunderstood. if you want to do the iso debate, i'm game, but let's take it over to the MF forum at photo.net and have some real fun!! as for the point about spot metering: about 50% of my work these days is LF urban landscapes. i can't imagine using anything but my pentax digital spot. indeed, with the exception of studio flash work, i can't imagine any application where careul spot metering isn't the best approach. the film doesn't care about ambient lite, all it knows is what is reflected onto it from the subject. why not measure what is actually being recorded by the film rather than making a bunch of assumptions about what SHOULD be reaching the film based on an incident reading. further, how can you really get a handle on subject briteness range (and so make zone decisions or even just determine whether the film can record your subject briteness range) without a spot meter. finally, it is rare when you can approach a landscape subject to make incident readings, and even when you can, it is entirely too subjective a matter deciding how deep in the shadows to place the dome. incident readings are for studio flash -- that's it. all the best, roger.

-- roger michel (michel@tcn.org), June 07, 2002.

Bob,

As for reproduction work it is obvious you can almost ever use an incident meter in relation to the distance.

However, to get a proper exposure indication you must use a flat diffuser, parallel to the document plan, which is not provided with all incident meter (my Sekonic on has this option).

Then, you can be for whatever reason devoid of an incident meter :))

In which case the gray card is better than "guesstimate"...

Friendly.

François

-- François P. WEILL (frpawe@wanadoo.fr), June 08, 2002.


Roger,

Sorry to say that but I think you are still not understanding the incident metering is the only way to meter accurately to retitute the 18% gray tones of a subject as 18% gray.

Your meter is calibrated for the 18% gray and the incident measure will give you exactly the reflective metering reading of a standard gray card as hold in place of the subject. In fact the incident meter just give you the reading of 18% of the light it receive while taking an average of all the light received by the subject.

If you use reflective metering, you'll get the same reading as an incident one if this zone is 18% reflective, a darker tone will lead you to OVEREXPOSURE as this darker tone will be restituted as if it was 18% reflective, while metering a lighter tone will lead you to UNDEREXPOSURE as it will be restituted as if it was 18% gray.

The test is easy:

Take three cards and give them the same amount of light:

One is white, the second 18% gray and the third black.

Take an incident measure of all the three and you will get exactly the SAME reading. Expose you negative this way without correction and you will end up with a white print of the white card, a 18% gray of the gray one and a black one of the black one.

Now make a reflective metering of each and expose accordingly without correction.

You will get an 18% gray rendition of the THREE.

So incident metering is the ONLY WAY to get a proper "technical" exposure without correction.

With reflective metering, unless you select a zone which is 18% reflective as you metering area, you will end with an incorrect exposure.

The easiest way to reflective metering is to take into account an area if the subject which is 18% reflective and receive an average amount of light for the subject.

If one of these conditions is absent you must apply an appropriate corrective factor to your measure.

Now in application of Ansel Adams Zone system, for a better and more personal rendition of the subject, SOMETHING WHICH IS AN ARTISTIC INTERPRETATION AND NOT A TECHNICALLY ACCURATE METERING, you can be lead to consider this or that area will be restituted on the print as IF it was 18% gray. This is an "interpretative reflective metering" and has nothing to do with a "scientific and technical" metering.

In incident metering the meter will eliminate 100 - 18 = 82% of the light received to give you the accurate reading. your subject will NEVER reflect more light than it receive (otherwise your subject is an illuminant - otherwise a source of light - itself). All the light it will reflect is part of what it receive. So the meter element through the diffuser will be actuated by all the light it receive but only take into account 18% of this light to give you the reading an 18% gray card under the average light received will reflect. So the accurate average exposure for the subject... Then what is 18% reflective will be translated into 18% gray zones, darker ones will appear darker (they reflect less) and lighter ones will be lighter (as they reflect more).

Friendly.

François P. WEILL

-- François P. WEILL (frpawe@wanadoo.fr), June 08, 2002.


FPW -- i don't really follow all that you say, however, i will try to formulate a response. to start with the bottom line -- and your last point -- of course what i'm interested in is interpretive metering. my goal is to put the scene on the negative (and ultimately the print) in a way that corresponds with my artistic vision of same. to do this, i need to know the relative values of various elements of the scene and the brightness range of my subject. it is difficult if not impossible to obtain this information from an incident reading. as to how an incident meter works, without quibbling with you about the photo standard (12 or 18% reflectance), you must understand that all an incident meter can tell you is how much lite is striking the subject. you must then undertake a subjective evaluation to determine how much light is being reflected back to the film. a reflectance meter, on the other hand, will give you a direct and absolute reading in EVs (or other units if you prefer) of how much lite is being reflected back to the film -- i.e. what the film is actually going to record -- as well as the relative values for various parts of the subject. at that point, you know enough to compress or expand contrast if you wish (through over/under-ex and over/under-dev) or to place parts of your subject in a zone that corresponds to its real life appearance, or on another zone to suit your atistic vision. while it is possible to do some of these things with an incident meter (although it is very difficult to measure true subject brightness range), it necessarily involves an extra subjective step -- or a leap of faith. and where a scene is unevenly lit, placement of the dome becomes a highly subjective (and very dodgy) matter. and let's not even get into the whole question of translatig color values into gray scale.

-- roger michel (michel@tcn.org), June 08, 2002.


Roger I’m sorry but you still do not understand how an incident meter works!

I will comment later what you say about the application of the Zone System, but let’s deal first with the main point.

You write:

>>… you must understand that all an incident meter can tell you is how much lite is striking the subject… <<

Which assertion is entirely FALSE. An incident meter doesn’t tell you the amount of light falling on the subject but uses the average light falling on it to give you a reading of how much of this light will be REFLECTED by an 18% (this is the internationally recognized standard and I don’t know from where originates your 12%) gray card.

So it is exactly equivalent to the reflected metering you will obtain from a gray card metered by reflection and lighted by the average of light falling on the subject. This is why it is calibrated.

I cannot but recommend you to read the Hasselblad Manual by Ernst Wildi where the subject is treated in the simplest and clearest way I ever see. I have the fourth edition (English) of it and it is treated in chapter 10 page 133 in this edition.

Then you write:

>> a reflectance meter, on the other hand, will give you a direct and absolute reading in EVs (or other units if you prefer) of how much lite is being reflected back to the film -- i.e. what the film is actually going to record -- as well as the relative values for various parts of the subject <<

Which is also totally wrong, but for the appreciation of contrasts by difference, because your reflected metering will give you a reading which correspond to what a 18% gray reflects (Zone 5 in Adams way) under this light it is submitted to.

As a darker than 18% gray surface will reflect LESS of the same amount of light than the 18% gray this will give you a reading which will indicate you a lower EV value (or if you prefer a wider aperture for the same speed or a slower speed for the same aperture) than your meter will have indicated if this surface had been 18% gray. So, without proper correction you will OVEREXPOSE the negative and in turn get this darker zone as if it has been an 18% gray zone. On the contrary, if you meter on a lighter zone, as the reflection will be increased for the same amount of light received, the direct reading will give you a higher EV value so you will close your aperture or increase the shutter speed too much so UNSDEREXPOSE the negative and finally end up obtaining an 18% gray zone on the print instead of a lighter one. This why, but if you take your reading from an 18% reflectance gray zone (or any percentage corresponding to the calibration of your meter if it is not the international standard), you need to correct your reading by a certain factor.

Now, another point is important in reflective metering and due to the limited amount of contrast which is possible to record on the film when compared to what our eyes see: for a negative the measure should be taken in the darkest zone of the shadows where you want to record details and with slides in the lightest zones (highlights) where you want some detail.

Now about interpretative metering:

If you use Ansel Adams zone system to record a lager panel of gray tones than with standard (objective) metering then be sure that Zone 5 areas of the subject won’t be recorded as 18% gray tones on your print but lighter or darker but the relative values of the scene will be compressed or extended to record more details having different gray tones. This is very interesting when you face subjects having a total contrast between details you want to record exceeding the film range. But it is in no way a technical exposure where the 18% grays of the subject are recorded by 18% grays on the print.

As to the transition of a colored world in gray scale, I gave on this board sometimes ago some examples and recommended correction extracted from Wildi book. For example of things to be considered 18% gray in the nature Wildi quotes between others sun tanned Caucasian faces, the green of grass and brown earth. If the reflective metering is taken on such subjects no correction is needed for a technically correct exposure.

Friendly.

François P. WEILL

-- François P. WEILL (frpawe@wanadoo.fr), June 08, 2002.


Bob, I am relieved to see that I'm not the only one with a voracious meter in his M. Mine too has eaten its share of pics. Boy, what an appetite! ;-) Take care, and feed that meter.

-- Olivier (olreiche@videotron.ca), June 08, 2002.

Now, for something a little more serious: Roger, François, I am not as smart as you are as far s metering is concerned. I usually trust my camera's meter (M6, now M7) and meter on an area I FEEL (or sometimes compute by taking several meterings) will give me the best average, or, intentionally, emphasize the important area of my pic, shadow, hightlight or in-between. I don't use exp. comp. much (on automatic metering), I prefer to go manual or AE lock where I need to (that's why I love the M7!) But I have one question: isn't reflective metering with a hand held meter exactly the same as metering with your camera's built-in meter? Isn't the difference only in terms of size of area metered? Or is there some kind of different calibration? Thanks.

-- Olivier (olreiche@videotron.ca), June 08, 2002.

FPW -- this is the last post for me on this. you are making less sense all the time. an incident meter MEASURES the lite falling on a subject. if you don't understand that, just stop reading here. it then takes that measurement and tries to gve you a reading about how an average scene will reflect that lite, BUT IT CAN REALLY ONLY SUPPLY A GUESS ABOUT ANY PARTICULAR SCENE BECAUSE AN AMBIENT METER HAS NO WAY OF KNOWING WHAT THE TRUE REFLECTANCE OF THE SCENE IS. as you say, all it can tell you is how an 18% (really 12%) will reflect that lite. a reflectance meter has te capacity to measure the ACTUAL NUMBER OF LUMENS BEING REFLECTED ONTO THE FILM. it can also be used to tell you the relative briteness of elements of the scene. from this you can accurately guage subject briteness range. in short, the reflectace meter measures WHAT THE FILM ACTUALLY RECORDS. an incident meter tells you about ambient lite levels, and from that you (or it) can make educated guesses about reflectance.

-- roger michel (michel@tcn.org), June 08, 2002.

and yes FPW, an incident meter will give you a very fair idea of what a grey card will measure in the ambient lite (assuming no specular hilites), but what the hell use is that??? you need to know the actual reflectance of the elements of your scene to expose properly, not how a grey card will behave. you can good at guessing zones, but there is NO WAY TO TAKE A DIRECT RELECTED LITE MEASUREMENT, and this is the true key info. an incident lite meter requires you to make lots of assumptions about reflectance. a reflected lite meter measure the actual lite striking the film.

-- roger michel (michel@tcn.org), June 08, 2002.

Roger, thanks for your interesting and very knowledgeable comments, but, please, stop shouting. You know that capital letters (except after following a period) are the equivalent of shouting, of course, right? Oh, now I understand why you NEVER use capital letters at the beginning of sentences after a period. You reserve them for shouting. ;-)

-- Olivier (olreiche@videotron.ca), June 08, 2002.

Olivier,

All TTL metering systems are based on reflective method like a hand held meter used this way. However on hand held meters (hand held spotmeters or angle reducing adapters set apart) the angle of measure is so wide you need to meter very close to your subject to select a proper usable zone or can't obtain anything valuable.

There are many ways the TTL metering are implemented though.

On Leica M (and Hexar RF) the system is generally described as "heavily centerweighed" which to a certain extent (but less than with a spotmeter) permits to select a proper metering area for the subject (hence the crucial role of the AE lock on an AE camera: meter, lock and recompose).

On the opposite an old Leicameter - Cds version(non TTL), using the reflective metering system meter the scene within an angle of 30° which, using a 50mm lens having a 45° field is very wide and covers most of the field of the lens and which is obviously wider than a 135 mm field (18°)...

Most of the old selenium hand held meters have a metering angle even braoder (some reach almost 90°!).

Both hand held and TTL meters are calibrated the same...

I hope It gives you the information you required

Friendly

François P. WEILL

-- François P. WEILL (frpawe@wanadoo.fr), June 08, 2002.


FPW, Roger - If I may, allow me to intervene here. It seems to me that the "discussion" is revolving around the same points, but assumptions are being made about specific elements that are being left out of the descriptions of the technique, resulting in the misunderstanding.

I think everyone understands that the incident meter is measuring the light falling on the subject, and in theory will give an accurate exposure that allows the various values in the scene to fall in their natural relationship - what I like to call the subject's "true tonality" (as stolen from Dean Collins). That assumes, however, that the light falling on the various portions of the scene is even and consistent. And, it doesn't consider the capability of the film to render all of the luminence values in the scene. In other words, highlights might exceed the film's capability at the high end, and shadows might fall below the film's capability at the other end of the response curve. But, the incident reading (again, assuming even lighting) would render the middle values correctly.

The procedure that I believe Roger is referring to is taking spot readings of various small portions of the scene, and then calculating an actual exposure setting, based on those readings, that will place the luminence values where he wants them on the film's response curve. In other words, he is not exposing at the actual value suggested by the reflective meter, but rather "interpreting" the readings to achieve what he wants on the negative, and potentially making considered compromises in the process. Depending on the range of reflectance values in the scene, it may or may not fall within the range of luminence values the film is capable of recording. If not, there is the option of adjusting development to either compress or expand the range of values to better fit the curve of the film. Such development adjustments are practical and relatively easy to do with single-sheet large format film, but impractical with 35mm film exposed in a Leica.

Both methods work, and incident readings, consistently made (assuming that one can actually meter at the subject position), will produce negatives of consistent density. But, those consistent, incident-based negatives may sacrifice detail at either or both ends of the luminence range. Using interpretive spot readings, once one has figured out the system, simply gives greater control over what is captured on film.

-- Ralph Barker (rbarker@pacbell.net), June 08, 2002.


thank you ralph -- i think you've covered it, at least mostly. i was also trying to point out the difficulties in using the BTZS techniques (i.e. incident readings plugged into phil davis' "calculator" to produce a zoned exposure), as compared to the comparative ease of a spotmeter. frankly, having been in the field many times with BTZSers, i just can't fathom why anyone other than a studio portarit photog would use an incident meter. you can't do ao many things, and in the end i just don't have enough faith in the concept that an incident reaing will yield a good exposure. i feel much more confident measuring the actual lite hitting the film. and once you factor in zone issues, there is really no comparison. how DOES an incident reading type guage subject briteness range; how does he place zones where he wants them, etc etc. AND AS FOR CAPS, i certainly don't mean to have them interpreted as SHOUTING. i never shout. i use caps for emphasis. i would prefer to underline, but don't know how to do that. if people interpret caps as shouting, i'll use the caps more selectively. sorry.

-- roger michel (michel@tcn.org), June 08, 2002.

Thank you for your explanations, François. And, Roger, you're forgiven. You know I am picky as far as punctuation, correct spelling and capitalizing are concerned. I've already posted something around that subject a couple of weeks ago. Two reasons: one, I think it's just more harmonious and more elegant when the basic rules of writing are respected. Two, it's much easier to read. Again, your posts are a pain to read because of the lack of capitals. It's a shame because they are goo and instructive, but I avoid them because they give me a headache. I am farsighted and I have to lean forward and move back as I try to see where the periods are, ie what the sentence means. And I thing you deserve more than to call yourself a little « i ». ;-) Take care, and thanks for your comprehensive and interesting posts.

-- Olivier (olreiche@videotron.ca), June 08, 2002.

roger:

To underline here use < U > followed by < /U >

as in see

Art

-- Art (AKarr90975@aol.com), June 08, 2002.


Hey, guys - What I've read above reminds me of the ancient story about the monks arguing about how many angels could dance on the head of a pin.

In the real world - - where you have either seconds or a short time to decide your apature and speed setting, I just take an incident meter reading, apply it for the first exposure - - - and then bracket.

C'mon, guys. Exposure for M series 35mm Leicas isn't rocket science. You grab either a reflective meter setting from your M6x or a hand-held meter, then shoot. Bracketing should be second nature!

Now. For carefully-designed shoots - - - complete with tripod, cable release, incident meter reading, spot meter reading, and incanations unto the spirits - - - you still want to bracket to be certain that what you want to put on film is really there. Variances in fiilm and shutter speeds demand that.

Just my three cents of shooting since 1945.

George

-- George C. Berger (gberger@his.com), June 09, 2002.


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