Sunny 16.

I'll have to look at this again tomorrow, I'm on my way out just now.

The RGB=101 above seems to be for 13% grey the same site gives RGB=118 for 18% grey which is around what I was getting and I think is also the same as the page Stefan referred to.

I'll check this tomorrow.

Yes my last site say 118 is 18% grey on the histogram, 12% should be 97.
you can test it easily.
Take a photo of a white paper and expose so the meter says it's spot on, the white should now be the grey it meters for.

Just took a shot.
numbers are with a 101 by 101 average:
R 96
G 95
B 94

this the math Luminosity = 0.3 R + 0.59 G + 0.11 B so...
0,3 x 96 + 0,59 x 95 + 0,11 x 94 = 95,19
We agreed that 118 is 18% grey and I said 12% was 97
Seems the K10D meters for 12% grey (or close to it) and not 18% grey.

Blimey!.. Sunny sixteen works in the dark, too!

Last night, I tried a little experiment. One of my favourite subjects is night street film photography. I have tried it a few times, but generally have been very disappointed with the results, almost always getting unscannable negatives, either far too dense, or blown out.

Using the chart provided by Don, above. I can guess that my night street scene is going to be at least two stops dimmer than the dim, overcast conditions given for the f5.6 setting. I estimated that I would use 30th of a second at f2.8, with 400ASA film.
So, off I go into the night, with a fifty year old Mamiya Ruby rangefinder camera, and no meter, walking up and down the main street, shooting everything at 30th and f2.8.
I developed the film this evening. - Every frame is nicely exposed. Good detail in shadows and highlights. Every frame easily scannable/printable.
Before, I was using the camera's meter to set the exposure. It was setting shutter speeds of a quater, a half and even full seconds!. Thats why I never got good night shots. The meter was trying to expose everything as an 18% grey, average.

You see! - Sunny sixteen knows best!

arguing over semantics like 12% or 18% is moot...
that would be a half stop at best, and may explain why photogs were over rating (or was it under rating???) thier slide film in the day.. I used to shoot kodachrome 65 at 50..... and used a kodak 18% grey card or the spot meter in camera...

the point is the rule works and understanding it gives you a reference point when your camera meter might read incorrectly.

It can be counter productive to over-think these things!

I've just had a look at this again and done a quick test with the camera. A straight shot of a white or grey card would be 101R 101G 101G in RGB space as per the results on this site. This is of course for half a stop below 18% grey which is 13% grey (12.73%). That page also gives values for +1 stop above 13% which is half a stop above 18% as RGB 137

All we really need in practical terms is the values of RGB that represent under and over exposure in half stops. This is handy if we include a grey card in a manual flash shot and want to know if it's shown correctly as 18% grey on the computer screen. Note we aren't metering off the card it's merely a known reference. Some of these were given others I've calculated.

The values are:

- 1 stop = RGB 85
- 1/2 stop = RGB 101
+- 0 stop = RGB 118
+ 1/2 stop = RGB 137
+ 1 stop = RGB 162
+ 1.5 stops = RGB 188

I can now properly set up my flash

Indeed when shooting I only think about the photo but at home processing the photos things sometimes gets complicated

About the grey card, I wonder if there aren't two versions around there.
One according the ANSI standard so 12% and the other neutral grey so 18%
Would need to check out various card at the shop I think ^^

I've only ever heard of the 18% grey card Stefan. 12% would be too dark to be any use on digital, in fact 18% is too dark for digital

Well no because the card is darker your camera overexpose relative to the 18% grey card. And since 12/13% seems to be what the camera meters you get the right exposure actually

The question is are those cards presented as 18% grey for photography exposure truly 18% grey are do they simply use the name since everyone thinks you need 18% grey?

It's all to do with noise Stefan. This video partly explains it. Worth looking at the other videos as well.

The Kodak Grey Card is a known standard even though it may not be exactly neutral because it was made for B&W. I sometimes use a grey Pure Evoke 3 remote control as a grey reference as well as a Kodak card.

Can you tell me around what time off the video since I've no idea what you mean with noise or what kind of noise.
I went through the first 3 points.

I think you mean the light grey part or not?
But this all about white balance and not exposure.

It's true more information is captured at the right/brigth end of the spectrum so you actually need to use a darker card because the camera will over expose that to make it grey.

I don't have any links handy, but it's more or less covered in the theory about exposing to the right of the histogram. More bits are available to store RGB information in the lighter areas.

For exposure as long as you know how many stops higher the reading is it's easy enough to compensate for it. You could take a reading off a white sheet of paper and expose for 3 stops less or 2.5 stops if you want detail recording in the white paper. Similar to taking a reading off snow.

I haven't the slightest idea what Algi and Anvh are talking about. All that theoretical stuff is way over my head... But I do know this:

Because of the Sunny sixteen rule, I can correctly expose just about anything, by memorising FOUR exposure values (or rather the combinations of shutter speed and aperture that make them). EV8, for night street scenes. EV12, for dull, overcast winter days. EV13, for bright, but cloudy conditions, and EV15,(The Sunny sixteen) for very bright sunny days with hard shadows. - Just knowing (and remembering) these four settings, means I can leave my camera on manual. And use any camera ever made, however old and basic, knowing I will get the exposure about right.

I think we should all know this.

There was a famous American wedding photographer in the 70's who had fixed exposure settings for everything on a wedding from bright sunlight right down to candlelight which was "wide open at 1/8th sec. handheld" (if I remember correctly.

When I was at school (in the 60's)one of out teachers had a Johnsons Diary with an exposure calculator that was made of stiff card that rotated around a rivet. You had to dial in location (long, lat from a table). Time of day. Type of lighting, sunny, cloudy bright etc. and then read off the exposure.