Thanks, Bill and Bill, for adding clarity to this discussion!!
Thanks, Bill and Bill, for adding clarity to this discussion!!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."
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.
Another one in denial.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."
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.
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
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.
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.
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 ...
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.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.")
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.
Yeah, I get that.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.
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.
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.
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, 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 ;-)
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.
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.
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