Getting the right exposure the first time

Started Jul 8, 2012 | Discussions thread
Graystar
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Setting Exposure - Part 1
In reply to Marathon Man, Jul 8, 2012

Marathon Man wrote:

I just came back from a trip in DC. I enjoyed very much working on getting the right exposure. To do so, I used both the histogram and the highlight mode.

I often had to either under (mostly) or over expose.

I use aperture priority and I have ISO setting always in manual.

My question: is there a way to always get the exposure right the first time or must I always look at the results of a test shot in order to compensate?

You have to go old-school...like back in the film days when there was no image review.

There's no way around it...to be able to set exposure correctly the first time you need exposure knowledge. You need to understand how the meter works, why it gets fooled, and how to use that to your advantage. It's nice to get the exact exposure you want on the first try, but be aware...if you want to take control of exposure then you have to actually do it...there's no faking it. Not like those people who shoot in manual mode to have "full control" of their cameras...and then use Matrix metering (the “P&S” metering mode.) Your metering successes and failures will be entirely your responsibility. Few people actually want this, as metering is a skill that must be developed, and in the beginning you get more shots wrong that you get right. But you'll get better with practice, and the reward is that you can get the exposure you want from any scene.

The basic premise is to spot-meter a known tone (or a tone you can guesstimate well) and to use that tone to set your exposure. On top of that basic skill you'll add techniques for constant-light conditions and changing-light conditions, depending on your camera's abilities.

If you spot-meter an evenly lit white wall and take a picture, you'll get a gray image where the RGB values are about 100, 100, 100 (note that picture controls and other processing can change the RGB values.) The meter works by first presuming that the scene is a gray of RGB 100. Then, it sets exposure so that you'll get an image that is a gray of RGB 100. If you meter a white wall, you still get the same gray. The camera can't tell what the actual color is of anything in front of it. Same if you meter a black wall...the image still comes out gray. So a camera will underexpose images of bright tones (such as a snowy landscape,) and overexpose images of dark tones (such a black cat.) The meter is being fooled, because it's always assuming that everything is gray.

The easiest way to get "correct exposure" (a debatable concept to begin with) is to simply give the camera what it wants...give it something gray to meter. That's what a gray card is all about. You hold the card in the same light that's illuminating your scene, meter the card, and now everything is exposed properly for that light. This works because ultimately, it's the light source that dictates exposure. Exposure is set for the light source, and then everything under that light comes out correctly exposed. That's why studio photographers use incident light meters...those meters measure the light directly. Our cameras have reflective light meters...the camera has to guess at exposure based on the light reflected from the objects in the scene. But white can reflect 90% of the light...black can reflect as little as 5%. How does the camera know which is which? It doesn't. As I said, it simply assumes all is gray. This assumption is fairly close most of the time, and works well for things like vacation and picnic snaps. But when you raise the bar and start shooting subjects in isolation, the meter is more wrong than right. So you have to introduce exposure knowledge into the mix, and correct the exposure yourself.

Exposure knowledge refers to knowing how the meter will react to various tones. So let’s say you don't have a gray card. If you're photographing a person with light skin then you can meter the skin, apply +1 Exposure Compensation, take your shot, and the exposure will be correct. That’s exposure knowledge. If you're shooting a snowy landscape and you want the snow to be white, you can meter the snow and set your EC to +2.3 (+2.7 if you’re really in tune with your exposure.) Your snow will now come out white.

Over time, a photographer will become familiar with the corrections required for his preferred subject matter. For example, on his website, photographer Jim Doty Jr. lists some EC values he uses in his landscape photography...
white sand, +2
birch bark, +1.5
yellow aspen leaves, +1
grass, +0
evergreen trees (no new growth), -1
buffalo mane, -1.5

If you spot meter any of these objects and apply the correct EC, you'll get correct exposure.

So that’s what photographers did in the film days, and it still works in the digital age. But what I described is simply a practice that applies to photography in general. Next you have to learn how to apply this practice on your particular camera. See the next part for that...

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