Kodak grey card usage

Diapositivo · Mar 23, 2016

markbarendt said:
"erratic" Giggle, those techniques aren't new. They are just different than today's norm.

The disk measurement is standard fare in a studio even today.

Aiming the meter at the light is one of the most accurate ways to meter, it just requires a little thought.

Practice with just the meter, leave the camera at home, just meter and try to see what it's telling you and see how many ways you can find to get to the same camera setting.

Yes, I did not mean to say that, in general, aiming at the source is wrong. As I said, that's normal practice, especially with a disc and in order to establish lighting ratio.

What I meant is that in our case of the flour, where you know the incident reading will give you an exposure which will be a bit excessive, I would rather just manually diminish the exposure.
If you point the light meter toward the light source you are obviously obtaining the same effect (the resulting exposure will be certainly inferior by some degree and it will protect the highlights). What I mean is that, at that point, I would rather manually choose the degree of compensation rather than relying on an indefinite correction, which might be more or less depending on the angle of the light source.

If the light source is very lateral, and you obtain 1.5 EV more exposure by pointing the light meter directly at the source, would you use that exposure, in our flour case? You wouldn't. You will tell me: the exposure given by the light meter is just a starting point. It's something that the photographer mumbles upon. And I agree. That's why I wouldn't make the second measurement at all. It wouldn't give me more information than what I already have.

Having the first, normal reading (sphere pointed at the lens) the white subject requires 0.5 EV or so less exposure regardless of how bright and how lateral is the main source. I just need to move it a bit along the characteristic curve and place it in the linear stretch. A second measure does not give me an added degree of precision or safety, I mean. Although I am sure pointing the light meter at the source would certainly produce the same kind of result.

BrianShaw · Mar 23, 2016

So.... doesn't that basically take us back to square one (1), not that that is a bad thing: a meter, reflective or incident, used with or without a grey or gray card, is capable of providing a light measurement that may or may not to determine a photographic exposure, but will be "in the ball park" and provide a reasonable approximation based on a bunch of various assumptions, some of which may or may not be true in all circumstances, but that light measurement and its exposure approximation can be altered by human judgment, based on the rules/principles of sensitometry, physics, and/or art, which may be fine or not fine, as well as the known characteristics of the photographic materials and processes being used, to determine the photographic exposure that the photographer implements to capture the chosen image in the way said photographer desires said image to be rendered.

cowanw · Mar 23, 2016

wiltw said:
But then there is also the fact that 18% grey only happens to be 'in the middle between the tonal extremes of white and black' and is NOT truly a good metering target for exposure.

As to the variability of angle, this illustrative series shot under overcast conditions when specular reflectivity is less an issue, and exposed per incident meter reading (ISO 400, 1/250 f/5.6 +0.3EV), a series of shots taken with the 18% card at a continuously moving (tilted) angle both horizontally and vertically. Note only frame 7, which is tilted per the Kodak instructions cited by RobC, appear truly similar to the midtone surrounding grey.

We are well beyond this post, but I was still lying awake thinking about this.
In point of fact, each picture shows the card reflecting the same percentage of the light falling on it. And if you moved your camera angled into the correct position relative to the card, rather than moving the card angled to the camera, each card position would look like #7.
The light suffusing the scene does not change, but by pointing the camera 10 different ways you can have 10 different correct exposures.

wiltw · Mar 23, 2016

Diapositivo said:
Having the first, normal reading (sphere pointed at the lens) the white subject requires 0.5 EV or so less exposure regardless of how bright and how lateral is the main source. I just need to move it a bit along the characteristic curve and place it in the linear stretch. A second measure does not give me an added degree of precision or safety, I mean. Although I am sure pointing the light meter at the source would certainly produce the same kind of result.

What you are proving is that each of us have our practiced methods for better achieving success in different situations. Bravo.

The point of my experiment was NOT to prove 'which method is best', but to compare methods and see how they differed from one another, or were similar in net result, so that others reading this thread could decide for themselves which method to adopt. So I followed the suggested technique of metering and adjusting by some factor, vs. other technique (e.g. flat disk aimed in different directions, and hemisphere aimed at different directions) to find if there was a method which would result in 'same exposure' but without the need for 'Kentucky windage' (to borrow a rifle shooting technique's name), "you decrease bit...".
Then I published the result of this comparative test, for the benefit of others who may not have much command of incident techniques...many simply use the incident reading without non-specific windage ("a bit"), thinking it is the surefire method (wrong). And how much windage is 'a bit', when we try to quantify it for others to follow (you had not yet stated 0.5EV at that point, if I recall)? And different photo workshop teachers teach 'aim at source' vs. 'aim at lens', and fail to consider the hemisphere vs. flat disk in the discussion! The end result is a confused student wondering "which technique is 'right', the one I use or the one workshop instructor uses?"

Ergo, that comparative test.

markbarendt · Mar 23, 2016

Diapositivo,

IMO, the classic incident reading isn't excessive, it's just a number that needs to be considered. The meter reading pointed directly at the sun asks us for less exposure, not more. It suggests specifically by measurement the diminishment you suggest be done manually, I assume by judgement based on experience. The manual diminishment you talk about is a judgement call. In contrast, pointing the meter at the main light provides a real number that we can use, it does the maths for us used in that manner.

We gotta remember though that when we are talking about protecting the highlights we are talking about protecting the positive image. We are looking ahead in the photographic process, the camera can't do this by itself. To truly peg the highlights with camera exposure we have to know exactly how we are going to get our positive.

Push and pull can change the highlight cutoff point. In the plate example above the classic incident metering method or the classic gray card measurement can be used to place camera exposure and then the meter reading pointed at the sun or gray card tilted toward the sun and asking for less exposure can be judged to be telling us "you need to reduce process contrast to straight print the highlights". For a slide, that can be a pull or we can decide to give away shadow detail and mid tone placement; for negatives we can do a pull or use softer paper or burn and dodge or give away shadows and specific placement like with a slide.

The extra readings very much give us information that is usable.

wiltw · Mar 23, 2016

BrianShaw said:
So.... doesn't that basically take us back to square one (1), not that that is a bad thing: a meter, reflective or incident, used with or without a grey or gray card, is capable of providing a light measurement that may or may not to determine a photographic exposure, but will be "in the ball park" and provide a reasonable approximation based on a bunch of various assumptions, some of which may or may not be true in all circumstances, but that light measurement and its exposure approximation can be altered by human judgment, based on the rules/principles of sensitometry, physics, and/or art, which may be fine or not fine, as well as the known characteristics of the photographic materials and processes being used, to determine the photographic exposure that the photographer implements to capture the chosen image in the way said photographer desires said image to be rendered.

Yup! ...which is why all the analytical debates about what reflectivity card is the right percentage to use with a reflected meter is rather amusing to observe. "Your mileage WILL vary (regardless of the darkness of the card!)!" and we have just proven that "Your mileage does vary" even with incident (which leads to Kentucky windage)!

wiltw · Mar 23, 2016

cowanw said:
We are well beyond this post, but I was still lying awake thinking about this.
In point of fact, each picture shows the card reflecting the same percentage of the light falling on it. And if you moved your camera angled into the correct position relative to the card, rather than moving the card angled to the camera, each card position would look like #7.
The light suffusing the scene does not change, but by pointing the camera 10 different ways you can have 10 different correct exposures.

the camera was NOT 'pointed 10 different ways'...if you observe carefully, there is an object in view (a wooden bench fixed to the deck) which is always in view in every shot...the CARD was angled differently but the camera was in fixed position and the card was in a fixed location (but angled differently)!

If I aimed a spotmeter at the rotating card, the meter reading would have changed simply due to relative angle of the 18% grey surface, and this apparent brightess change is seen in the photo series as 'different brightness card' using a fixed shutter speed and aperture (as the same-exposure of the surroundings proves). This series also shows that the precise angle has effect on apparent brightness of the card, so the changing Kodak how-to-use recommendations over the decades has a real and proven effect on consistency of readings over the years! Ergo, all the debates about what is the right technique for using a grey card (and even how dark of a grey card to use).

markbarendt · Mar 23, 2016

cowanw said:
We are well beyond this post, but I was still lying awake thinking about this.
In point of fact, each picture shows the card reflecting the same percentage of the light falling on it. And if you moved your camera angled into the correct position relative to the card, rather than moving the card angled to the camera, each card position would look like #7.
The light suffusing the scene does not change, but by pointing the camera 10 different ways you can have 10 different correct exposures.

You are right that the characteristics of the card don't change.

Changing the camera position doesn't change the way we want to render the scene.

What does change with card angle is what light falls on the card.

BrianShaw · Mar 23, 2016

markbarendt said:
...

What does change with card angle is what light falls on the card.

... and how the light is reflected by the card.

Diapositivo · Mar 23, 2016

Mark yes, of course I meant 1.5 EV LESS exposure. I said "more" because, you see, the EV value is higher... (and so the exposure is less) and sometimes I express myself improperly. You are correct +1.5 EV means less exposure, naturally. (I tend to have the lightmeter talk to me in EV parlance). You understood what I meant.

The manual diminishment you talk about is a judgement call. In contrast, pointing the meter at the main light provides a real number that we can use, it does the maths for us used in that manner.

In my opinion also pointing the meter at the main light is a judgement call. If the light is at a steep angle, that's not really the light that the lens sees. You will certainly end up with less exposure but you risk overshooting and risk having the flour "not white enough".
As the useful experiment by wiltw shows, angles matter.
So IMHO by pointing the meter at the light source you have a "pseudo-precise" way of doing things. It mostly works the same way, of course, but it's not less judgemental and, in my humble opinion, is even riskier, because it gives you different compensations with different angles of main light to subject-lens axis.

The simple rule I gave is more constant and, IMO, more reliable. Take a normal incident reading (sphere, toward lens) and, for white subjects, add 0.5 EV to the EV value the lightmeter gives (close half step). That will move it a bit toward linear response of the film and keep it white.

markbarendt · Mar 23, 2016

wiltw said:
"Your mileage does vary" even with incident

The tool is fully capable of doing the job, our understanding is the limit.

markbarendt · Mar 23, 2016

BrianShaw said:
... and how the light is reflected by the card.

you bet

MattKing · Mar 23, 2016

markbarendt said:
You are right that the characteristics of the card don't change.

Changing the camera position doesn't change the way we want to render the scene.

What does change with card angle is what light falls on the card.

BrianShaw said:
... and how the light is reflected by the card.

Actually, I think Mark is wrong, and Brian is mostly right.

The light that falls on the card isn't changing, although in some cases the card ends up shading itself.

What does change is the light that is reflected by the card toward the camera.

And it is that light that affects our metering.

So any attempt to use the Gray card for metering should use a technique that is repeatable in nature, and effectively correlates the light reflecting from the subject of the photo toward the camera, with the light reflected by the card toward the camera.

cowanw · Mar 23, 2016

Wiltw, Yes I understand what you did.

Markbarendt, I think what I was saying that to fulfill the angle requirements of the camera card placement, In a relative world the camera could be moved instead of the card. this would mean the background behind the card would change; The light hitting each new background scene differently (at different angles also), would, in my head, make each new scene require a different exposure which would then make the Grey card look as in #7.
This is just another way to say that having the sun to your back or to your front may make a different exposure without any change in the amount of light flooding the scene
( I took too long to type)

markbarendt · Mar 23, 2016

cowanw said:
Wiltw, Yes I understand what you did.

Markbarendt, I think what I was saying that to fulfill the angle requirements of the camera card placement, In a relative world the camera could be moved instead of the card. this would mean the background behind the card would change; The light hitting each new background scene differently (at different angles also), would, in my head, make each new scene require a different exposure which would then make the Grey card look as in #7.
This is just another way to say that having the sun to your back or to your front may make a different exposure without any change in the amount of light flooding the scene
( I took too long to type)

Yep.

cowanw · Mar 23, 2016

In another thought, It has been said that grass or cement of the correct tone can double as a grey card. Good luck getting the grass to lie in the correct plane to make the angles right, not to mention getting the blades of grass to line up 1. For those who use the palm of the hand as a Zone 6, do you angle it as well.
It's hurts my head when I think about these things

BrianShaw · Mar 23, 2016

Grass... I read that too but can't put my finger on it right now. I remember the suggestion for where dark green grass vs light green grass would lay in the scale. But here is SoCal most grass is some shade of tan or brown due to the drought... if it hasn't already been replaced by a non-oxygen-generating alternative.

Bill Burk · Mar 23, 2016

wiltw said:
the camera was NOT 'pointed 10 different ways'...if you observe carefully, there is an object in view (a wooden bench fixed to the deck) which is always in view in every shot...the CARD was angled differently but the camera was in fixed position and the card was in a fixed location (but angled differently)!

If I aimed a spotmeter at the rotating card, the meter reading would have changed simply due to relative angle of the 18% grey surface, and this apparent brightess change is seen in the photo series as 'different brightness card' using a fixed shutter speed and aperture (as the same-exposure of the surroundings proves). This series also shows that the precise angle has effect on apparent brightness of the card, so the changing Kodak recommendations over the decades has a real and proven effect on consistency of readings over the years! Ergo, all the debates about what is the right technique for using a grey card (and even how dark of a grey card to use).

wiltw,

Your demonstration is beautiful and shows how much the angle matters when using the gray card to stand as proxy for metering just before you take it away and shoot the subject without the gray card in it. Since you used the same shutter speed and f/stop for each shot, the background stayed the same.

But... if you had taken the meter reading for each shot and changed f/stop or shutter speed for each shot... all the gray cards would have looked the same as the background image varied. It would be bad for the purpose of pictorial photography to be inconsistent in the angle of the gray card. But if you are taking the photograph for calibration purposes, for example to read the density of the gray card on the film... it really wouldn't matter much what angle you hold it. If you meter from the camera position - the meter would always tell you to change the shutter speed or f/stop until to give the same gray every time.

Bottom line: If you weren't aware of the angle to hold the card and were calibrating or shooting film tests - you don't have to throw out your film test results. They would be valid regardless of the specific angle. (I'm sure you tried to eliminate really bad errors like extreme angles and the angle which maximizes glare). But if you are taking pictures metering off the gray card and then pulling the gray card out of the picture to shoot, you should angle the card consistently from now on... now that you know.

markbarendt · Mar 23, 2016

MattKing said:
Actually, I think Mark is wrong, and Brian is mostly right.

The light that falls on the card isn't changing, although in some cases the card ends up shading itself.

What does change is the light that is reflected by the card toward the camera.

And it is that light that affects our metering.

So any attempt to use the Gray card for metering should use a technique that is repeatable in nature, and effectively correlates the light reflecting from the subject of the photo toward the camera, with the light reflected by the card toward the camera.

The card, like an incident meter in lumidisk mode, is pretty directional. The card is effected by all the light hitting it not just the sun/main light and the more the source light deviates from perpendicular to the card the less it effects the reflection we or a spot meter can see coming from the card.

For example, if the sun is at a 45 behind the camera and we are shooting on a white sand beach and we tilt the card from perpendicular to the camera so it "sees more sky and less beach" the light falling on the card and the reflected light heading from the card to the camera will change, the reading from the card in this case may even suggest more camera exposure. Black sand beach, the same change in card tilt may result in the meter suggesting less exposure. This happens because the aggregate light the card "sees" and can reflect has changed.

wiltw · Mar 23, 2016

Grass vs. grey card...I just did that. Grass varied from -1.1EV to -1.7EV compared to a grey card layed on the grass (so both were at similar angles to the morning illumination. I gave up on grass and foliage as a metering surrogate a very long time ago, too much variability.

I decided to do my card angled series again, this time taking a set of photos with my back to the location of the sun (although I was in shade for the card) and then with the card at right angles to the sun. I incident metered ONCE for exposure for the entire series (ignoring the change of angle to the sun) with the hemisphere pointed in the direction of the illumination (shaded sun) which was also where my lens was: ISO 400 1/1600 f/2.8 +0.1EV. Nevertheless, I did incident meter with sun at my left (and meter to my lens), to quantify the change in light intensity to be consitent with the toward-the-lens orientation of the incident meter.
Shots 1-8 are with sun at my back, shots 9-15 are with the sun at my left. The main point of this series is the illustration of the criticality of the angle of the card, but also that the card angle can HIDE the variation in exposure caused by change of the position of illumination source vs. subject...shot 2 looks quite like shot 12, even though in theory the incident reading for shot 12 is -0.5EV from shot 2. And #5 looks like #11, again in spite of incident reading for shot 11 is -0.5EV from shot 5. If one compares #5 vs. #13, with similar angling of the card to the lens, one can see some of the lower light condition of shot #13 as expected. but the illumination difference is clearly visible in #1 vs. #9.

cowanw · Mar 23, 2016

Thanks for the extra examples

Stephen Benskin · Mar 23, 2016

A potential problem with metering foliage is the higher level of IR. Many meters are sensitive to IR and will register such a subject as being brighter than it truly is. One way to check whether a meter is sensitive to IR is to aim it at a TV remote and meter with and without activating it.

RobC · Mar 23, 2016

Kevin Caulfield said:
Sorry, but I can't resist...

It's "it's" not "its".

touché !

markbarendt · Mar 23, 2016

Diapositivo said:
In my opinion also pointing the meter at the main light is a judgement call.

Surely. Every exposure setting is a judgement call.

Movie sets are a good example of a place where pegging to the highlights is used.

The reason for this is the consistency that they can get across an entire body of work. The scenes look normal, dark scenes look dark, light scenes look light, and the people in them look like they belong there.

That consistency is huge. All the frames are typically developed the same way too. They need a solid baseline.

Pegging to the highlights allows the director's judgement and biases in specific situations to be measured and adjusted to accurately.

Diapositivo · Mar 23, 2016

In thanking wiltw for his illustrative tests, I am pondering that they really show why incident light meter are graciously provided with a lumisphere. Their use would be quite error prone if we had to devise any time the exact proper angle at which to use them. The lumisphere takes a lot of complexity out of this. Gives us the light "around the subject" not the light "mostly perpendicular to a certain plane of the subject".

On the other hand, if a subject is plane, such as a dark wooden table, that we want to photograph while maintaining, in the slide, the dark tone of the wood:

- supposing we are using an incident light meter we would obtain more precise results by using the disc instead of the sphere;

- supposing we are using a grey card for whatever reason, I think we would obtain more precise results by placing the grey card flat on the table, and not at a certain angle. We would then read the spot metering on the grey card laying on the table, and we would have the result we would use if the table was grey. Then we would close 1 stop because we want the wood to be dark.

Using the grey card on the same plane of a plane subject (document, painting, mosaic, fresco, pavement, floor, manhole, table...) corresponds to the use of the disc. If the flare on the card is very different from the flare on the subject, we are going to have a less precise indication.

Orienting the grey card half-way between source and lens-subject axis is an attempt to average the light "around" the subject just like a lumisphere would do. That is also a way to try to minimize flare, probably.

But if the subject IS flat and if it has flare, then the disc or card laying on the plane should give a better reading.

Kodak grey card usage

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