burkphoto Loc: High Point, NC

Light is particles (photons) traveling in electromagnetic waves. The frequency correlates with our color perceptions. ROYGBIV where red is relatively low and violet is relatively high frequency.

BHC Loc: Strawberry Valley, JF, USA

"Why 18%?"

Maybe, just maybe, because it works!

David in Dallas Loc: Dallas, Texas, USA

I believe that I read many years ago (MANY years ago) that the 18% gray card was intended to be approximately the reflectance of a more or less typical Caucasian's skin, and thus could be used to set exposure for portraits or other scenes involving people. (Of course, it's been a long time since this "fact" could be uttered or admitted.) That would explain, however, why using the palm of one's hand is a suitable substitute.

Pablo8 Loc: Nottingham UK.

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Was it 'SUSAN' that Kodak used for the promotion ?

Tomfl101 Loc: Mount Airy, MD

My method for perfect exposures is to use a simple small white sheet of paper. Purposely overexpose a test shot, then stop down until the "highlights-over" stops blinking. Once this is achieved you will have detail in all white objects with all other tones (including blacks) falling into their true and correct tonality with little or no need for post adjustment. I prefer this over a gray card because it's fast and easy, and it can be packed in a shirt pocket. Incident meters are notoriously inaccurate and don't take into account variations from different chips, shutter/aperture variations. Particularly useful if you're a jpeg shooter and have little room for error. I have even used this method for ratio lighting in a studio.

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

This has nothing to do at all with the OP's thread. GF is talking about white balance, not exposure settings.

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

A couple of clarifications.

I generally agree with how you are setting exposure. In principle I do almost the same thing - in principle. Rather than use a piece of paper, I use the spot meter in the camera to target the brightest element in my scene. When shooting birds, for instance, it is usually chest or tail plumage, or the whole thing if it is a white bird. I have previously determined that I can add up to 1-1/3 exposure to the reading and not have blown highlights. No need to bring paper or walk out onto the middle of a lake to ensure that the subject, which might fly away when it sees you step into the water - decides you are a threat and flies away.

The piece of paper and looking at the overexposure warning (or the histogram) method works well for jpeg because the blinking warning is based on the jpeg preview. If you shoot raw, you'll find even more headroom which is why you test ahead of time.

But not all scenes include the tonal value of a white piece of paper. If your subject is a black bird in a tree, setting your exposure using a white piece of paper will result in an underexposed bird. In this case you will get a better exposure of the bird by finding a good balance between metering the bird directly (resulting in a middle gray bird), and underexposing the bird slightly to make it a little darker as you record it. You'll have more data to work with in post, which means you'll have more range between the noise level and the actual image data to work with, resulting in less overall noise.

Using your method or mine, the range of tonal values of the rest of the image will determine how much post processing work you'll have to do to get the image to look right. If there is direct sunlight falling on the subject and the subject is highly reflective, like an egret gull or swan, and there are deep dark shadows everywhere else, you bet you are going to need to do some serious tone adjustments in post processing.

The best current incident meters do provide the ability to accurately profile the meter to the camera, so the inaccuracy is hardly an issue anymore.

This method works best for raw, because of the greater dynamic range, but it can be used with great success for jpeg when you have 100% control over light levels (like in a studio setting), or with low to medium contrast scenes. Higher contrast (greater dynamic range) becomes a challenge for jpegs.

You can read about the method of using a bright element in the scene to determine exposure here:

https://teejaw.com/fred-pickers-zone-vi-workshop/

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

Caucasian in the middle of summer in a southern climate maybe. In the days when dinosaurs roamed the earth chasing little cavemen with mechanical cameras (I remember those days quite well), untanned Caucasian skin was considered to be up to one stop more reflective than middle gray. There was even a Zone System advocate that created a system that was similar to Ansel Adams, and named it the Zone VI workshop.

https://teejaw.com/fred-pickers-zone-vi-workshop/

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

Ar first read, I havegreat reluctance agreeing with you, but after some reflecting on it for a bit you are definitely making total sense . . .

(sorry, you left the door open on that one).

Seriously, your method (also mine) results in zero exposure errors and can be used in 100% of your images with full confidence. That being said, I use a flash meter in studio - much more accurate at determining ratios than the Zone System.

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

Here is a good explanation of 18%, 12% the printing industry, the difference between reflectance and luminosity, etc etc.

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

Sage advice and much better than the highly touted Peterson book "Understanding Exposure."

Tomfl101 Loc: Mount Airy, MD

The original post is "Why use 18% for METERING". Your analysis is correct if the goal is for reduced noise levels in dark objects (as it should be) Using my method the bird would be correctly/accurately exposed and appropriately black. Pushing exposures "to the right" is always desirable when post processing is your regular workflow. But if and when your images must be sent directly to a lab or news outlet for processing, you can't count on auto-exposure lab equipment to render your work correctly. Most of us are simply looking at our camera screens and making quick evaluations on the fly. When you have the opportunity to use a gray card or white card you have the best chance of getting it right without the estimated interpretation needed to evaluate a reflective meter reading. You make good points however and I appreciate your incite.

PhotoMike5319

Thanks Kiwi1. I agree that the people who learn to shoot film first have an ability to recognize how to fix a digital image that has an exposure problem because of their experience in the darkroom learning how how to control exposure and contrast when making a traditional silver print. The closest equivalent that I have experienced with my digital cameras was learning the nuances of "exposing to the right" when examining the digital histogram provided by my camera. Thomas Knoll (Adobe expert who works for Adobe) explained it best. Basically the histogram is divided into 5 zones (similar to but not the same as the zones in the Zone System). The zone farthest to the right (representing the lightest tones of the image) contains half of the pixel information in the image. So for my 10 megapixel Pentax, that zone contains 5 megapixels of the sensor information. This is approximately the zones 7 and 8 and above in the old zone system for film. The next zone on the digital histogram contains half of the remaining pixels. So for my 10 megapixel Pentax, that zone contains 2.5 megapixels of sensor information. The middle zone of the digital histogram then contains half of the remaining pixels, just 1.25 megapixels for my camera, and approximates zone 5 in the old zone system for film. This is where light meters attempt to place the exposure when the camera is in an automatic mode, halfway between absolute black and absolute white; in other words 18% gray.

Continuing on, the remaining two zones contain half again. For my pentax, that would be 0.625 megapixels then 0.3125 megapixels respectively. The farthest left digital zone, which contains the least information, represents the darkest tones in the image. this would be approximately Zone 3 and below in the old zone system for film. So if someone wants a truly white wedding dress of a bride standing in the snow, they need to expose the image so that the dress ends up where the most information is stored in the digital file - thus expose to the right- and then the ecru, cream, egg shell,etc (go to a fabric shop and count the various shades of "white" that are available to make cothes with) can be distinctly separated in a digital print. Then using the LEVELS tool and the CURVES tool in your favorite editor can digitally correct your dark tones to what is desired. Where Ansel Adams said to expose for the highlights and develop for the shadows has been modified to expose for the highlights (to the right) and adjust for the shadows (fix it in post).

For those who need to see some excellent examples, read "Monochromatic HDR Photography" or "The Photographer's Black & White Handbook", both by Harld Davis. Mr. Davis shoots in color and converts last. He also explains how it all works technically far better than my short synopsis. Read a little and learn a lot, it doesn't hurt.

blackest Loc: Ireland

no thats wrong its easiest to think of it as 5 sections of tones when dividing the colors into tones the highest tones have twice the values of the tone below it thats when the signal is recorded as a line once its a jpeg its had a curve applied to it.

Maybe watching this will help
https://topdownvideos.com/training/tone-mapping/

these are values for each individual pixels how the values are distributed in the scene depends on the scene if we had a snow ball in a coal mine most of the pixels would be in the bottom tones very little in the midtones and a relative few would be in the highest zone . the pixels with the highest values would be the ones for the snow ball but most pixels would have low values (the coal mine).

Does that make sense to you?

canon Lee

Keep in mind that exposure is about whites and blacks. The most important is mid tones, because it contains most of the details and contrast. I read that the mid-tones value comes from an "average" from most peoples sight. However no matter what camera you are using, mid-tones are most valuable. Editing in LR is excellent when using the "shadow" slider, which are the mid tones ...