Newb question about metering

Horoscope Fish

Horoscope Fish

Senior Member
The single biggest misconception about light meters, I think, is this: The job of the light meter is to correctly render exposure.

This is is simply NOT correct. Put this idea OUT of your head and getting the exposure you want will be a cake walk.

Drill into your head what the light meter’s job REALLY IS: providing you with a consistent, objective measurement based on a known value for you, the photographer, to make a subjective decision on regarding exposure. This is not just semantics. This is, I believe, a crucial turning point of understanding regarding how metering and exposing "works" in photography.

The light meter does not assume: it objectively measures and calculates. The light meter does not get “fooled” or make the “wrong” suggestion: It objectively measures and calculates. The light meter is a tool of guidance; it is not the photographic equivalent of exposure "auto pilot".
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J

J-see

Senior Member
The meter is great to keep control over clipping. That's why I about always use highlight metering when doing landscapes with much sky, or any other scene where light rules. I could care less what the meter considers correct or not but I do care a lot about what makes it into my RAW.

To do that, the meter is a very handy tool but even when using it for those specific scenes, I do need to check the clipping since I can never fully depend upon what the meter indicates.
 
W

WayneF

Senior Member
Al Gentile said:
"I'm still working on grasping 18% grey though."

Back in the early 1900s, Kodak engineers determined that if, in a 'typical' scene, you averaged all the colors and brightnesses, you'd end up with the color grey that reflected 18% of all the light that fell on it. Thus, light meters were calibrated to assume that they were always pointed at an 'average' scene, and would recommend the proper combination of aperture and shutter speed (for the given ASA [ISO]) that would correctly render the proper exposure. Although that's clearly sometimes a mistaken assumption, it makes more sense than to assume the scene was always brighter or darker than normal.
Click to expand...


Print shops did use 18% cards for many years before photography, to judge their ink levels on a 50% screen pattern. It is a human eye response thing.

But actually, for photography, 18% was all Ansel Adams idea, with his Zone System in the 1930s (printing analog film on analog paper). The first light meters started about then too, and Kodak always advised if metering on their 18% gray card, to open aperture half a stop more. Which is 12%, which is how modern light meters calibrate (Sekonic, Nikon, Canon, all 12.5%. Others like Minolta used 14%, about 1/6 stop different). Kodak and Adams had many discussions, and due to his influence, it seems Kodak did not choose to make an issue of the number. Kodak sold some media business parts (including the gray card) twenty years ago, in 1995, and this half stop advice was generally lost then. The Kodak cards thereafter were NOT from Kodak.

Gray cards are sort of an analog film thing, 18% is near middle gray. Digital is different, 18% is 18%.

What is interesting is that so many think photographing a gray card ought to appear at histogram midpoint. But the word Middle has many uses... :) 18% is 18%, and in digital form, it ought to appear at 18%. However, our histograms are always gamma encoded, which makes 18% shift to about 46%. Which is near middle, and not a large error, but an error. But a really HUGE error in concept, 18% has nothing to do with histogram 50%.

Conceptually, it might be best to think in terms of middle gray.
 
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