Ansel adams moonlight equation
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Let’s face it… the guy was a great photographer and a great self promoter. He loved to share his knowledge and loved to tell stories. To be honest, it really doesn’t matter how much is fact, fiction, or slightly embellished. Being a “bullshitter” is a charming attribute… and he was a very charming man!
MattKing
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AA didn't need to meter the moon - he knew its luminance - how much light was reflecting off of it - 250 c/ft2.
That was what determined his exposure settings, because the moon was the subject (mostly) of his photo.
He knew how that amount of luminance translated to settings on his camera, because he used Weston meters that gave readings in c/ft2, and because he had used the dial on the meter enough to remember what combination of aperture and shutter speed worked with 250 c/ft2 and the film he was using.
Just as many of us may remember how particular readings (e.g. EV?) on our meters translate into shutter speed and aperture combinations.
The most esoteric part of this is that AA remembered the luminance of the moon. The rest is just particular to the units of luminance he was comfortable using.
That was what determined his exposure settings, because the moon was the subject (mostly) of his photo.
He knew how that amount of luminance translated to settings on his camera, because he used Weston meters that gave readings in c/ft2, and because he had used the dial on the meter enough to remember what combination of aperture and shutter speed worked with 250 c/ft2 and the film he was using.
Just as many of us may remember how particular readings (e.g. EV?) on our meters translate into shutter speed and aperture combinations.
The most esoteric part of this is that AA remembered the luminance of the moon. The rest is just particular to the units of luminance he was comfortable using.
I read the story too… a long time ago. 1978 or 1979, in fact. The amazing part to me is that he actually knew what unit of measure was on the meter. Most folks seem to not know, and not care!
The old Westons were very useful for more than just photography. I used a Weston III to do initial lighting assessment on industrial workplaces. That use of engineering units made it more than just a photographic exposure meter.
For more detailed initial assessment we used a Pentax digital spot meter, which was a pain in the backside because we had to convert the reading to engineering units. One more step and one more chance for inadvertently making mistakes.
The old Westons were very useful for more than just photography. I used a Weston III to do initial lighting assessment on industrial workplaces. That use of engineering units made it more than just a photographic exposure meter.
For more detailed initial assessment we used a Pentax digital spot meter, which was a pain in the backside because we had to convert the reading to engineering units. One more step and one more chance for inadvertently making mistakes.
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But the Weston meter dial was not in c/ft2, it was in foot-candles! Low: 2 to 50, High: 25 to 1,600 foot candles, as I stated earlier in post 19
http://www.jollinger.com/photo/meters/other/weston-article.html
He had to convert the meter scale to c/ft2 , if he could have found the meter. It was indeed esoteric he remembered the c/ft, not being able to find the meter in his rush to get the shot rapidly.
(Note: Retraction per Post 42, about Weston meter dial units. Quoted statement in link was wrong!)
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No matter… conversion of units isn’t exactly a black art. 
But I’m pretty sure that Weston III, at least, reads in Cd/sqFt. Ironically… the manual doesn’t state what the units are. Nor does the Weston IV manual.
the Weston V manual has a procedure any table for conversion between units. (Page 23).
update…. The Weston Master II manual specifies, on page 1, “candles per square foot”.
But I’m pretty sure that Weston III, at least, reads in Cd/sqFt. Ironically… the manual doesn’t state what the units are. Nor does the Weston IV manual.
the Weston V manual has a procedure any table for conversion between units. (Page 23).
update…. The Weston Master II manual specifies, on page 1, “candles per square foot”.
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Being a "bullshiter" is a charming attribute? The name Trump comes to mind!
The Weston meter reads in Cd/ft^2 and AA is very familiar with this type of measurement. He called it foot candle but that is a misnomer because foot candle is a illuminance measurement which AA never used. He only dealt with luminance. His formula that he liked to use requires to know the lumance of subjects in Cd/ft^2 and thus he knew the values for various things by heart.
No matter… conversion of units isn’t exactly a black art.
But I’m pretty sure that Weston III, at least, reads in Cd/sqFt. Ironically… the manual doesn’t state what the units are. Nor does the Westin IV manual.
update…. The Weston Master II manual specifies, on page 1, “candles per square foot”.
The scale on the Weston III and Weston IV look just like the scales on the Weston Master and Master II...max reading is 1600 (foot-candles)
The Master V and later meters left off the hundreds, and show '16' as max scale.
The Weston 650 (a.k.a. Leicameter) scale (predating the Weston Master, showed 'shutter speed at f/5.6 and f/32', scale maxed at 1000
(Note: Retraction in Post 42 for units of measure)
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sigh.
In 1941, AA would have been using a Master II... wouldn't you agree? I cited the manual.
Weston was quite consistent in this regard... even with their truncation of the numbers!
In 1941, AA would have been using a Master II... wouldn't you agree? I cited the manual.
Weston was quite consistent in this regard... even with their truncation of the numbers!
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Looney f/11 is just a rule of thumb, like sunny f/16: daylight exposure in full sun is about f/16 at 1/ISO, so f/16 at 1/125 sec for ISO 100 film. You can read about sunny f/16 in most introductory photography books.
The rest of what I wrote is mostly converting from one f-stop - shutter speed combination to another, like f/16 and 1/125 is the same exposure as f/8 and 1/500 sec. Again, you can read about that in most introductory books. It may help to get a book that was written in the film era and before fully program-auto cameras. I also used a filter factor conversion - Ansel's yellow filter cut the light by about 3x, he said - which again is covered in any intro book. There are photography blogs that mention these things, but they often get things confused, which is why I'm suggesting a book. The two volume "Ansel Adams Guide to Basic Techniques of Photography" edited by John Schaeffer would tell you all of this and more.
The only really obscure fact that I used in the exposure calculation is the history: ASA was redefined in about 1960 and film speed numbers changed by about one stop. For everyday photography, no one needs to know this, it just helps to interpret events before 1960.
MattKing
Moderator
The scales on the Weston Master II actually read in foot candles per square foot (a measure of luminance), not foot candles (a measure of light source intensity). There is a conversion utility built into the dial which allows you to take incident readings and convert the foot candles per square foot readings into foot candles. The Ollinger description mis-speaks, because foot candles makes no sense in a reflected light meter.
If there is a conversion on the dial I'm not aware of it. Would love to learn something new about these old meters, though. (I still use my Weston IIIs on a regular basis.) I know in the Master V manual there is a conversion table, which was not in the prior versions.
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That is correct but AA in his book often called the unit Foot Candle which is the incorrect term.
Chrome intensifier. He botched the exposure
That illustration of the manual is convincing, candles/square foot. Information I previously used was provided in http://www.jollinger.com/photo/meters/other/weston-article.html
" On the Universal the ranges are Low: 2 to 50, High: 25 to 1,600 foot candles." appears to have gotten units wrong.
This article identifies the confusion and inconsistency. https://www.westonmeters.info/light-units
"Weston light meters, including the luminance as well as exposure meters, are not consistent in the units that appear at the end of the needle pointer when it moves in response to the light. Once you attempt to compare one meter model with another it gets confusing. Indeed, even within one model - such as the S85 - the units can differ. So what do there different units spread across the scale amount to?
"I have made some attempt here to understand and explain them (with the help of Wikipedia). I hope I've got it right. If any reader of this page can contribute to or correct the information, I would appreciate it. - So here goes:
"Although not actually mentioned on the majority of Weston exposure meters, the unit in most common use is candles per square foot, or Candles/Ftsq. This is NOT the same as foot-candles although the simple relationship between the two terms means that a Weston meter can be used to convert between them. Early Weston light meters call this 'Light Values'. On the Master series, just the term 'Light' is most commonly used."
Yet an illustration of two luminance meters shows very clearly Footcandles on the dialface of models 703 and S85.
Apologies for the earlier contradiction, Brian. All prior posts claiming foot-candles have noted retraction."I have made some attempt here to understand and explain them (with the help of Wikipedia). I hope I've got it right. If any reader of this page can contribute to or correct the information, I would appreciate it. - So here goes:
"Although not actually mentioned on the majority of Weston exposure meters, the unit in most common use is candles per square foot, or Candles/Ftsq. This is NOT the same as foot-candles although the simple relationship between the two terms means that a Weston meter can be used to convert between them. Early Weston light meters call this 'Light Values'. On the Master series, just the term 'Light' is most commonly used."
Yet an illustration of two luminance meters shows very clearly Footcandles on the dialface of models 703 and S85.
But given that these were not narrow angle spotmeters, how did AA get a reading of 250 c/ft2 ?!
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No problem. None at all. I noticed that it is incorrect on that site (jollinger) and correct in another paragraph.
So what? People liked the photograph enough to buy prints from him. Mission accomplished.
If you want to measure foot.candle you have to convert the meter to incident meter. He can't get the reading off the moon he knew it. He never measured it I don't think so.
Oh sure! But really his formula and his knowledge of the moon luminance isn't all that good for him. I am sure if he could redo the shot he would use a different exposure very like significantly more exposure.
He didn't take a measurement off the moon. He knew what the surface brightness of the moon was, because the moon is in full daylight. There may have been elaborations to the legend over the years ("This is the West, sir. When the legend becomes fact, print the legend.") But the basic idea is, he guessed the exposure for the sunlit moon using prior knowledge, and hoped/figured that the foreground in the setting sun's light would turn out.
I've seen a couple of different prints of this image at the Center for Creative Photography, and IIRC the way it was printed got more dramatic from early to late versions. It also required a fair amount of dodging/burning to get the image onto the paper the way he visualized it.
I've seen a couple of different prints of this image at the Center for Creative Photography, and IIRC the way it was printed got more dramatic from early to late versions. It also required a fair amount of dodging/burning to get the image onto the paper the way he visualized it.
MattKing
Moderator
He probably took earlier photographs with the moon visible in the sky, and therefore had experience with what works.
I immediately thought of Moon over Half Dome, but that was exposed 19 years after "Hernandez".
He would know the illuminance at the moon surface which is approximately the same as on earth but he wouldn't know the luminance unless he also know the reflectance of the moon surface.
I covered this in post #7 - the "looney f/11 rule." https://www.photrio.com/forum/threads/ansel-adams-moonlight-equation.185114/#post-2438414 It's a common rule of thumb that the moon's surface is a little darker than an 18% gray card, so instead of sunny f/16 you use f/11. This rule even has its own Wikipedia page: https://en.wikipedia.org/wiki/Looney_11_rule
St. Ansel didn't have wikipedia, so he used prior knowledge of the moon's luminance in surface brightness units, which is throwing everybody off because none of us are used to thinking in candles per foot^2. But for whatever reason, he thought and worked that way. I showed in post #7 that looney f/11 actually gives a very close approximation to the exposure he said he used, once you take into account that he put the moon on zone 7, filter factors, etc.
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