Feedback Please: The Kodak 18% Grey Card and Metering, a new look.

[Arvee]

Exactly. The exposure meter standard is all about measuring some quantity of light then using the main equation to express this as a combination of shutter speed and lens aperture.

The fine details of the standard(s) include specifics of the light source, tolerances, and that sort of thing.

The actual standard(s) include details of the "exposure meter calibration constant," 'K,' which includes variables Stephen has (somewhat cryptically) mentioned - they include such things as camera lens transmittance, camera flare correction factor, and "effectiveness" of the light source in producing exposure on the film. For example, you would expect different 'K' values if the film has a different spectral sensitivity, or lens/camera combinations have different amounts of flare potential.

A lot of the difficulty with understanding this comes from people trying to make it more complicated than it is, such as the error of saying that an exposure meter is "calibrated for 'x' percent scene reflectance."

Thanks, Bill and Bill, for adding clarity to this discussion!!

 

[Stephen Benskin]

Here we go again, half truths, smoke and mirrors.
I don't who wrote it or who agrees with them which you do. If I shine 1024 unts of light at anything it can only reflect at most 100% of 1024 units regardless of what type surface it is unless it's fluorescing. If the numskull that wrote that crap means that if the surface was not a matt surface but high gloss then it would reflect x percent in relation to what the matt surface reflects but not more than 100% of the light incident on it then it might make some sense. But that isn't what you said. And what has Mecury got to do with it or are you another one relying on telepathy.

It's all that science stuff again with its fancy logic, and me with actually including references instead of pulling stuff out of my ass. The Holm quote was from the paper Exposure-Speed Relations and Tone Reproduction which can be considered a primer. The paper was presented at the Society for Imaging Science and Technology 47th Annual Conference / ICPS in 1994. It's available at http://64.165.113.140/content/benskin/. Holm is an imaging consultant and has played a rather large part in digital camera exposure theory. My first experience with his work is from the Tone Reproduction entry in The Focal Encyclopedia of Photography. But I'm sure a guy who can't connect the dots between scene illuminance and film plane exposure is right.

Once again for everyone else. Reflectance is based on a Lambertian surface which is also known as a perfect diffuser. The equation for reflected light off a Lambertian surface is Illuminance * Reflectance / pi. This means that a surface with 100% reflectance doesn't reflect 100% of the light. Mostly when Reflectance is used it is referring to equivalent Reflectance. If the metered calibration point is at 12% Reflectance, what is the Reflectance of something five stops higher?

 

[RobC]

Exactly. The exposure meter standard is all about measuring some quantity of light then using the main equation to express this as a combination of shutter speed and lens aperture.

The fine details of the standard(s) include specifics of the light source, tolerances, and that sort of thing.

The actual standard(s) include details of the "exposure meter calibration constant," 'K,' which includes variables Stephen has (somewhat cryptically) mentioned - they include such things as camera lens transmittance, camera flare correction factor, and "effectiveness" of the light source in producing exposure on the film. For example, you would expect different 'K' values if the film has a different spectral sensitivity, or lens/camera combinations have different amounts of flare potential.

A lot of the difficulty with understanding this comes from people trying to make it more complicated than it is, such as the error of saying that an exposure meter is "calibrated for 'x' percent scene reflectance."

Another one in denial.
For K = 12.5

(B*S)/K = (B*S)*0.08 = (B*S) * 8%

Is that really so difficult. Most people wouldn't have a clue what K = 12.5 really means where as the the vast majority would know what 8% means. So given they are equal it makes understanding what is going on far eaier for most people without getting into the standards and derivation behind it. But Hey Ho we have some nerds who want to argue over scientific semantics.
As Konrad Lorenz said:
Every man gets a narrower and narrower field of knowledge in which he must be an expert in order to compete with other people. The specialist knows more and more about less and less and finally knows everything about nothing.

 

[Stephen Benskin]

The actual standard(s) include details of the "exposure meter calibration constant," 'K,' which includes variables Stephen has (somewhat cryptically) mentioned - they include such things as camera lens transmittance, camera flare correction factor, and "effectiveness" of the light source in producing exposure on the film. For example, you would expect different 'K' values if the film has a different spectral sensitivity, or lens/camera combinations have different amounts of flare potential.

Sorry I didn't want to be too overwhelming. Here are two pages from Defining K. Please note how the equations for q and K are almost identical expect for 4 additional variables in K.

 

[Mr Bill]

Rob please. Gimme a break. After you say, "Be kind," you completely dismiss my response like that. Okay, where, pray tell, are you getting YOUR information from. I hope you're not gonna tell me it's from the ISO 2720 standard. If so, check the date and see if it's not from 1974 (if it is, I guess you have to reconsider your position on "old" standards and meters, etc.).
http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=7690

Rob, please cut through all the talk. Where does your knowledge about this come from. Do you actually have a copy of the standard or not? If not, what source of information are you using about the 'K' constant?

 

[RobC]

How many times do I have to tell you people. You're a bit slow on the uptake. I'm not interested in being dragged down the mind numbingly boring standards route. They are 100% not required to take an accurate meter reading and going on about flare and derivation of the K Factor won't make your negatives any better and certainly won't make you a better photographer. if all you're interested in is standards then go and work for ISO, I'm sure its a thrilling place to work with lots of committee meetings to attend.

 

[markbarendt]

You are assuming I would expose for the shadows but I don't and nor does the example I gave. It uses the actual meter reading or meter reading opened up one stop. i.e. expose for middle of curve or one stop more than middle of curve.

Actually your example does tie to the shadows.

It's not about you "measuring for the shadows", it is simply that the ISO standard is tied to the speed point of the film and the Kodak card's reflectance is tied in a very specific relationship to the standard, and therefore to the shadows.

One can only peg one point on the film curve with exposure, the rest of the tones just fall where they fall.

To define a second point on the film curve, like say a specific mid or highlight tone, one must define the development regime.

Shoot to the shadows, develop for the highlights.

 

[Mr Bill]

Sorry I didn't want to be too overwhelming. Here are two pages from Defining K. Please note how the equations for q and K are almost identical expect for 4 additional variables in K.

Thanks Stephen. I really meant only meant that you had referred to some variable names that no one without a copy would know exactly what they are.

A quick look at your section "K = ..." shows that it is the same as in ANSI PH3.49-1971, EXCEPT for the 10.76 x pi part, which I'm guessing is a conversion. But thanks for what looks to be a pretty thorough write-up. (Anyone who really wants to dig into the so-called "K constant" should find it all here; most people have no need, but this reveals that there is no connection to "scene reflectance.")

 

[RobC]

circles of confusion.

 

[Mr Bill]

How many times do I have to tell you people. You're a bit slow on the uptake. I'm not interested in being dragged down the mind numjbingly boring standards route. They are 100% not required ...

You could have saved me a lot of effort by saying this when I made post #2 of this thread. You were the one bringing the K-constant into the fray by "interpreting" it into your write-up.

At least this thread seems to have been a little educational for at least a few posters.

By the way, my adult work life has been 100% full time in photography, including about 40,000 portrait subjects under my belt before I made a "temporary" excursion into lab work. Stop being so insulting about things you don't know about.

 

[SchwinnParamount]

Ok, based on Rob's original proposal: "...Also might enlighten a few people about light meter calibration in what I hope is as simple and readable and non scientific presentation as possible"

This discussion has gone off into the weeds. Buncha exposure nerds, I tell ya!

I believe Rob intended the article to be for the novice who doesn't care about and won't notice the difference between one interpretation of the zone system an another.

Before you object to something in his paper, ask yourself "Will this objection to some small detail make a REAL difference to the casual photographer who's trying to learn about exposure?" I certainly remember when I was trying to learn why the gray card was useful. The very last thing I would have been interested in reading was the discussion in the thread.

 

[Stephen Benskin]

The following is a brief look at the variables r and t.

 

[RobC]

Thanks Stephen. I really meant only meant that you had referred to some variable names that no one without a copy would know exactly what they are.

A quick look at your section "K = ..." shows that it is the same as in ANSI PH3.49-1971, EXCEPT for the 10.76 x pi part, which I'm guessing is a conversion. But thanks for what looks to be a pretty thorough write-up. (Anyone who really wants to dig into the so-called "K constant" should find it all here; most people have no need, but this reveals that there is no connection to "scene reflectance.")

The article says simple and non scientfic. The opening post of the topic says simple and non scientific. My post number 11 in topic says non standards. But no, you and a couple of others just can't help yourselves and want to hijack someone elses topic treating their requests for non standards based discussion with contempt and then cry foul about it when you demand proof from standards and are told where to go. Get a life.

 

[markbarendt]

Ok, based on Rob's original proposal: "...Also might enlighten a few people about light meter calibration in what I hope is as simple and readable and non scientific presentation as possible"

This discussion has gone off into the weeds. Buncha exposure nerds, I tell ya!

I believe Rob intended the article to be for the novice who doesn't care about and won't notice the difference between one interpretation of the zone system an another.

Before you object to something in his paper, ask yourself "Will this objection to some small detail make a REAL difference to the casual photographer who's trying to learn about exposure?" I certainly remember when I was trying to learn why the gray card was useful. The very last thing I would have been interested in reading was the discussion in the thread.

Rob's first words, "Feedback please"

 

[SchwinnParamount]

Rob's first words, "Feedback please"

Yeah, I get that.

Feedback should in some way relate to the original post. While it is true that arguing the minutiae of exposure is in the spirit of a gray card discussion, his clear indication that the document was for a non-scientific audience should have set the bar for the science in the responses.

 

[markbarendt]

Yeah, I get that.

Feedback should in some way relate to the original post. While it is true that arguing the minutiae of exposure is in the spirit of a gray card discussion, his clear indication that the document was for a non-scientific audience should have set the bar for the science in the responses.

Feedback comes as it comes, reviews are done to find problems the author didn't see.

So now he has feedback on his "draft 1", now he can rewrite as he pleases, and publish if he pleases.

 

[Mr Bill]

The article says simple and non scientfic. The opening post of the topic says simple and non scientific. My post number 11 in topic says non standards. But no, you and a couple of others just can't help yourselves and want to hijack someone elses topic treating their requests for non standards based discussion with contempt and then cry foul about it when you demand proof from standards and are told where to go. Get a life.

Please just go back to your article and remove the parts about the standards and the "K factor." This will help it be more "simple and non scientific." Then you can get back to your own life.

If you want to make the article simpler, why not just talk about your own experience metering from an 18% grey card, and how much exposure error you find? Then how much compensation is needed. You can probably support this with Kodak's grey card instructions? Maybe?

Does someone really need to understand an H&D curve to understand this? If you think so, I think you need to explain them more thoroughly, you might even list the alternate names so novice readers will realize they are all the same thing.

I appreciate how hard it is to write good articles; I've done plenty of them in the office for internal use. I typically would figure who the audience is, then pick someone I knew as the lowest common denominator, then all along the way, I'm thinking, "will Joe (or whoever) understand this?" Often I'll go through the topic in a simplified manner, but have an appendix (or similar) at the end, so anyone interested in more detail can get it there. A lot of this is sort of thankless - I may start out with a dozen pages, cut, simplify, redo part, cut some more, etc., and finally get down to 3 or 4 pages. (The parts I like best are often gone - they weren't crucial.) When it's done, people don't realize what went into it - they think you just sat down and wrote 4 pages, and that they could have done it too, because it seems so simple. That's my experience, anyway. I'm doing it in a corporate setting where I know that people won't bite into a long document, so I try to make it as brief and simple as possible (but not simpler). But if you're being paid by the word, you probably want a different approach.

I wouldn't want to be your editor, and I'm sure you wouldn't want me to either.

 

[Bill Burk]

You got what? I'm not trying to get anything. Its you trying to work out why some different formula or writing work out the same as the standard meter formula. I think the meter formula is the one to use.

One side of your equation:

(B * S) / K

Returns a numeric exposure value. An appropriate label would be meter candle seconds.

It's not Brightness or Luminance in candela per square meter anymore.

 

[BrianShaw]

After reading the entire (very interesting) thread, I read the manuscript. I have to agree with MrBill.

Rob: Suggest taking a look at what other authors have said in the subject ( literature review... Which I'm sure you don't want o do just like you don't ant to get into the details of standards... and I totally understand. But Roger Hicks explained the grey card and metering in Perfwct Exposure quite similar to your bottom line... Using only 4 or 5 paragraphs.

Best of luck to you wherever this effort takes you!

Please just go back to your article and remove the parts about the standards and the "K factor." This will help it be more "simple and non scientific." Then you can get back to your own life.

If you want to make the article simpler, why not just talk about your own experience metering from an 18% grey card, and how much exposure error you find? Then how much compensation is needed. You can probably support this with Kodak's grey card instructions? Maybe?

Does someone really need to understand an H&D curve to understand this? If you think so, I think you need to explain them more thoroughly, you might even list the alternate names so novice readers will realize they are all the same thing.

I appreciate how hard it is to write good articles; I've done plenty of them in the office for internal use. I typically would figure who the audience is, then pick someone I knew as the lowest common denominator, then all along the way, I'm thinking, "will Joe (or whoever) understand this?" Often I'll go through the topic in a simplified manner, but have an appendix (or similar) at the end, so anyone interested in more detail can get it there. A lot of this is sort of thankless - I may start out with a dozen pages, cut, simplify, redo part, cut some more, etc., and finally get down to 3 or 4 pages. (The parts I like best are often gone - they weren't crucial.) When it's done, people don't realize what went into it - they think you just sat down and wrote 4 pages, and that they could have done it too, because it seems so simple. That's my experience, anyway. I'm doing it in a corporate setting where I know that people won't bite into a long document, so I try to make it as brief and simple as possible (but not simpler). But if you're being paid by the word, you probably want a different approach.

I wouldn't want to be your editor, and I'm sure you wouldn't want me to either.

 

[RobC]

thats what everyone does and how myths, half truths and downright wrong information is perpetuated isn't it? It's also how people get stuck in a rut and won't believe anyone who says anything is wrong citing the fact that all the books say the same thing so anything different must be wrong. Well its no one wonder if you look at what every one else has done. Its why web sites all look the same. Its why design in general is fashionable becasue all the designers copy each other. Its how art syles become fashionable. Everyone is copying everyone else.

Nope, I'm just gonna write what I damn well want to write in next release which will be final release. I have noted a fair few comments and corrections for inclusion.

 

[Diapositivo]

RobC, as you know I initially wrote to you a comment by private mail and you did not reply to my doubts/observations while you and the other gentlmen were bickering over this K damned stuff ;-)

 

[RobC]

RobC, as you know I initially wrote to you a comment by private mail and you did not reply to my doubts/observations while you and the other gentlmen were bickering over this K damned stuff ;-)

I seem to remember that I did reply that I would address your comments in due course. I haven't got round to it yet but they have been noted. I seem to have lost your PM but I copied it elsewhere so have the notes you made for when I rewrite the article.

 

[Stephen Benskin]

The article says simple and non scientfic. The opening post of the topic says simple and non scientific. My post number 11 in topic says non standards. But no, you and a couple of others just can't help yourselves and want to hijack someone elses topic treating their requests for non standards based discussion with contempt and then cry foul about it when you demand proof from standards and are told where to go. Get a life.

First of all Rob, you can't set the conditions on how you want people to respond. BTW, you were using the maths first and using the exposure meter standard. So you are allowed to use it but nobody else can? Technically, I wasn't using the standard. I was using a paper that was later part of the appendix (not the standard) in one of the standards. And just in case you didn't know, K is part of the standard.

Secondly, I was trying to point out that meters are not calibrated to 8% (you have this fixation on Reflectance), but your default response is always belligerence, so I had no other choice than to bring out overwhelming evidence to show that K is mostly about the loss of exposure through the camera's optical system. I didn't expect you to accept it (you called a current leader in the field a numskull). It was more for the others. And when you are cornered on an incorrect statement, you pull out every logical fallacy in the book and eventually play the victim. My favorite is when you claimed you exposure meter was somehow different from all the others.

You've come along way since the time you were suggesting a 10 stop range was normal and everyone else was wrong, but simply studying the Wiki page and playing with the equations without attempting to integrate them into the rest of the process isn't going to do it. Read the supporting papers.

If you weren't from England, I'd swear you were a Republican (though probably an authoritarian never the less). Just a little hint, if you want respect, you have to give it.

 

[RobC]

as usual you've twisted it. As of now you are on my ignore list. I think you've let your ego get the better of you. I'm not looking for your respect. Sorry to disappoint you. Oh, and you had no other choice? We all can make choices except you it seems, you just can't help yourself. That's the problem. Goodbye.

 

[Stephen Benskin]

thats what everyone does and how myths, half truths and downright wrong information is perpetuated isn't it? It's also how people get stuck in a rut and won't believe anyone who says anything is wrong citing the fact that all the books say the same thing so anything different must be wrong. Well its no one wonder if you look at what every one else has done. Its why web sites all look the same. Its why design in general is fashionable becasue all the designers copy each other. Its how art syles become fashionable. Everyone is copying everyone else.

Nope, I'm just gonna write what I damn well want to write in next release which will be final release. I have noted a fair few comments and corrections for inclusion.

Can you also tell us about how climate change and Evolution are wrong? BTW, if any of us had a life, we wouldn't be spending so much of our Sundays on this site, and if I'm not mistaking, you spend far more time here than I do.