18% Grey Card. To use it or not.

[Milpool]

He once referred to it as moon over hernia if I remember correctly. No joke.

I can't tell you the number of times I've seen people write "Moonrise over Hernandez," and I always have the exact same thought as you--that is not what he titled the thing! I also continue to be amazed at how many times I see his last name written as "Adam's."

 

[DREW WILEY]

What difference does it make? If you have enough money to buy it, the gallery will figure out what you mean.

 

[Mike Lopez]

What difference does it make? If you have enough money to buy it, the gallery will figure out what you mean.

Thanks for the input, Andy.

 

[Alan Edward Klein]

If they were titled "Sunrise over Hernandez", I would have checked the provenance.

Even rarer.

 

[wiltw]

I've seen quite a few big Moonrise prints - after all, it was not only his most famous image, but by far, his most printed cash cow, over 350 of them.

No need for Photoshop. Michael Fatali simply sandwiched 8x10 chromes together for sake of optical Ciba enlargements, in one instance three of them, with both the rising moon and setting sun in astronomical impossible proximity. One should get suspicious of exactly the same crescent moon appearing in the same place in the sky in several different images. But the result was far more seamlessly precise, even in a 40X60 print, than anything digitally altered and printed.

Maybe I should revive the photo that I had AI create, of 'sunrise over San Francisco', AI showing the sun rising in the western sky?

 

[Chuck1]

Don't forget people so they can have odd hands and feet

 

[DREW WILEY]

When I bought and sold paint I made up a spoof color card with colors like Los Angeles Sunrise, dark brown.

When I comes to SF, I chuckle over the "blood moon" image arising above the Golden Gate Bridge well after sunrise, and about sixty times bigger in diameter than it would really appear. It was actually at its peak several hours earlier in a different position in the sky, while it was still dark. But that image got shown on the morning news, so it must have gotten all PS cobbled together awfully fast.

 

[Stephen Benskin]

This is from Jack Holm's paper Exposure Speed Relations and Tone Reproduction.

MI = Exposure Meter Index.
<Hg> = statistically average film plane mean exposure (lux-seconds)
H18% = film plane midtone exposure (lux-seconds)
<Lg> = statistically average scene mean luminance (candelas per square meter)
r = Lambertian (perfectly diffusing) surface reflectance
E = Scene illuminance (lux)

Holms uses 128% for highlight reflectance for the paper. Most sources use 100% reflectance. "These values result in the mean luminance correlating with a Lambertian scene reflectance of 12% for 100% highlight reflectance or 14% for 128% highlight reflectance." So his one third stop lighter than average would be 1/2 stop if 100% reflectance was used for the highlight making the calibration average luminance 12%.

Equation 10:

t = shutter speed
A = lens f/ number
K = exposure meter equation constant (luminance or reflected metering)
EI = Exposure meter Index

 

[Alan Edward Klein]

This is from Jack Holm's paper Exposure Speed Relations and Tone Reproduction.

MI = Exposure Meter Index.
<Hg> = statistically average film plane mean exposure (lux-seconds)
H18% = film plane midtone exposure (lux-seconds)
<Lg> = statistically average scene mean luminance (candelas per square meter)
r = Lambertian (perfectly diffusing) surface reflectance
E = Scene illuminance (lux)

View attachment 409299
Holms uses 128% for highlight reflectance for the paper. Most sources use 100% reflectance. "These values result in the mean luminance correlating with a Lambertian scene reflectance of 12% for 100% highlight reflectance or 14% for 128% highlight reflectance." So his one third stop lighter than average would be 1/2 stop if 100% reflectance was used for the highlight making the calibration average luminance 12%.

Equation 10:

t = shutter speed
A = lens f/ number
K = exposure meter equation constant (luminance or reflected metering)
EI = Exposure meter Index

View attachment 409300

View attachment 409307

What does this all mean and how would you use it? In simple language.

 

[Stephen Benskin]

What does this all mean and how would you use it? In simple language.

It's the explanation behind the use. Instead of just making a claim, I've included the proof. The diagram illustrates it. Conclusion, the exposure meter isn't calibrated to 18%, but you can use an 18% gray card to make an exposure.

 

[DREW WILEY]

Just how many commercial gray cards equate to a Lambertian surface anyway? Probably zero. That's why it's "Fuzzy Math".

 

[Bill Burk]

Tried to meter the moon the other day.

At first I thought it might be 250 candles per square foot so I went to test that assumption.

Setup this contraption, a tungsten light source with Kopp 5900 blue filter. Set the Sekonic L-758DR to ASA 100 and 1/250 and cranked up the light until it read f/10.

Dialed SEI photometers to match the light source. Then compared them to the moon.

The moon was less luminous by about two-third stops. About 160 candles per square foot.

-The moon is an object lit by the sun so it should be “Sunny 16”.

-Sunny 16 is 250 candles per square foot.

-But not at 18%, more like 12%.

-The moon has about 12% albedo.

-So the moon should be 250 candles per square foot.

Why is it closer to 160 candles per square foot?

 

[Alan Edward Klein]

View attachment 409367
Tried to meter the moon the other day.

At first I thought it might be 250 candles per square foot so I went to test that assumption.

Setup this contraption, a tungsten light source with Kopp 5900 blue filter. Set the Sekonic L-758DR to ASA 100 and 1/250 and cranked up the light until it read f/10.

Dialed SEI photometers to match the light source. Then compared them to the moon.

The moon was less luminous by about two-third stops. About 160 candles per square foot.

-The moon is an object lit by the sun so it should be “Sunny 16”.

-Sunny 16 is 250 candles per square foot.

-But not at 18%, more like 12%.

-The moon has about 12% albedo.

-So the moon should be 250 candles per square foot.

Why is it closer to 160 candles per square foot?

Wasn't there a big fight years ago that mid gray should be 12% not 18%? I think Adams or one of his friends was involved in the discussion. It might have to do with exposure for chromes vs negative film or reflective vs incident modes, but I don't recall the facts. Maybe your camera or light meter is calibrated to 12%?

 

[Stephen Benskin]

View attachment 409367
Tried to meter the moon the other day.

At first I thought it might be 250 candles per square foot so I went to test that assumption.

Setup this contraption, a tungsten light source with Kopp 5900 blue filter. Set the Sekonic L-758DR to ASA 100 and 1/250 and cranked up the light until it read f/10.

Dialed SEI photometers to match the light source. Then compared them to the moon.

The moon was less luminous by about two-third stops. About 160 candles per square foot.

-The moon is an object lit by the sun so it should be “Sunny 16”.

-Sunny 16 is 250 candles per square foot.

-But not at 18%, more like 12%.

-The moon has about 12% albedo.

-So the moon should be 250 candles per square foot.

Why is it closer to 160 candles per square foot?

I just got the value off a Google search.

Encyclopedia RP Photonics

luminance

Luminance measures the luminous flux per unit solid angle at unit projected area. It is related to visual brightness.

www.rp-photonics.com

The Moon 2500 cd/m2 or 232 cd/ft2

Google AI

The luminance of the full Moon is approximately 232.25 cd/ft². The luminance can vary depending on atmospheric conditions.

Conversion to cd/ft²
The luminance of the full Moon is most often cited in candelas per square meter (cd/m²), the standard international unit of luminance.

• Typical value: 2,500 cd/m².
• Conversion factor: 1 cd/m² is equal to about 0.0929 cd/ft².
• Calculation: 2,500 cd/m² × 0.0929 cd/ft² per cd/m² ≈ 232.25 cd/ft².

 

[Stephen Benskin]

Wasn't there a big fight years ago that mid gray should be 12% not 18%? I think Adams or one of his friends was involved in the discussion. It might have to do with exposure for chromes vs negative film or reflective vs incident modes, but I don't recall the facts. Maybe your camera or light meter is calibrated to 12%?

Meters are calibrated to Luminance not a Reflectance. However, depending on the what the highlight Reflectance is based, a Reflectance can be applied.

From Jack Holm, "That the mean log luminance of a statistically average scene is approximately 0.95 log units below the highlight log luminance (edge of detail in white) and 1.25 log units above the shadow log luminance (edge of detail in black), and that this mean luminance is assumed to be the luminance metered, directly or indirectly, for exposure determination. These values result in the mean luminance correlating with a Lambertian scene reflectance of 12% for 100% highlight reflectance or 14% for 128% highlight reflectance. Values ranging from 10 to 18% have resulted from various experimental determinations."

 

[Chan Tran]

View attachment 409367
Tried to meter the moon the other day.

At first I thought it might be 250 candles per square foot so I went to test that assumption.

Setup this contraption, a tungsten light source with Kopp 5900 blue filter. Set the Sekonic L-758DR to ASA 100 and 1/250 and cranked up the light until it read f/10.

Dialed SEI photometers to match the light source. Then compared them to the moon.

The moon was less luminous by about two-third stops. About 160 candles per square foot.

-The moon is an object lit by the sun so it should be “Sunny 16”.

-Sunny 16 is 250 candles per square foot.

-But not at 18%, more like 12%.

-The moon has about 12% albedo.

-So the moon should be 250 candles per square foot.

Why is it closer to 160 candles per square foot?

I think you're mixing foot candle and candela per square foot. As stated sunny 16 is an illuminance measurement in foot candle the refectance is not a factor. The brightness of the moon as seen from earth is a luminance meauserment in cadela per square foot and it does depends on the reflectance of the moon surface. The moon is said to have the reflectance of about 12%.

 

[BrianShaw]

Google AI

When presenting material from AI inquiries it might be good to also cite AI’s sources. AI don’t know much on it’s own.

 

[Stephen Benskin]

When presenting material from AI inquiries it might be good to also cite AI’s sources. AI don’t know much on it’s own.

This is what comes up clicking on the Lemniscate symbol.

 

[DREW WILEY]

Ai skims a lot of stuff floating to the top, like a sewage treatment pond.

 

[Alan Edward Klein]

Meters are calibrated to Luminance not a Reflectance. However, depending on the what the highlight Reflectance is based, a Reflectance can be applied.

View attachment 409387


View attachment 409388

From Jack Holm, "That the mean log luminance of a statistically average scene is approximately 0.95 log units below the highlight log luminance (edge of detail in white) and 1.25 log units above the shadow log luminance (edge of detail in black), and that this mean luminance is assumed to be the luminance metered, directly or indirectly, for exposure determination. These values result in the mean luminance correlating with a Lambertian scene reflectance of 12% for 100% highlight reflectance or 14% for 128% highlight reflectance. Values ranging from 10 to 18% have resulted from various experimental determinations."

I appreciate your hard calculations. Could you sum up in layman's terms what it all means?

 

[BrianShaw]

I appreciate your hard calculations. Could you sum up in layman's terms what it all means?

First sentence... and, perhaps, the second. Ignore the parts that you don't understand.

 

[Stephen Benskin]

First sentence... and, perhaps, the second. Ignore the parts that you don't understand.

Personally, I would suggest the part by Holm. The reasoning with the math will have to wait until I'm off work and there's more time.

 

[BrianShaw]

Personally, I would suggest the part by Holm. The reasoning with the math will have to wait until I'm off work and there's more time.

Without intent to disagree, but read the audience. The science and math are way beyond what most readers here will read, or understand. I'm impressed with your knowledge and your efforts for continued teaching!

 

[MattKing]

I like the fact that @Stephen Benskin includes in his posts both the conclusion and the math and scientific logic behind it.
Some of the math I can track easily. Some would require me to return to my youth. But the logic is really important to understanding the conclusion.

 

[DREW WILEY]

Now factor the influence of intervening atmosphere at any given time and place, and you'll realize why the effective luminance of the moon often differs quite a bit from the theoretical version.