The very first thing to remember about exposure is that it's an interpretive choice. It's true that it's partially a technical problem to measure the light and arrive at the value you want and apply it, but the "correct" exposure also depends on your aesthetic goals for the picture. Perhaps, but not necessarily, part of the further changes you plan to make in post-processing.
Second, often there's no such thing as one correct exposure. There is a range of choices, any of which will "work" but that contribute to different effects. The meter reading, no matter how you apply it, is only advisory. In fact, the exposure that is ideal for your interpretation of your scene might be quite far away from the meter reading.
The next thing to remember about exposure is that despite the broader range of corrections and manipulations that are available to photographers today in image-editing programs such as Lightroom et al., getting the ideal exposure from the start, in-camera, will contribute to a final result of the highest quality.
And the fourth important thing to remember is that there's no magic in how you arrive at a given exposure**. It's just a value. You get no points for having used this or that method of arriving at it—all that's just for your own convenience, and to suit your perceptions of what's going on and how things work. We all work based on the way we're comfortable with, and that best fits our conception of what's going on, and that we have the most experience with, and that suits the camera's capabilities. But there's no magic to how you get to the end result if the end result is the same. You're free to pick the method that you think works best for you and that you're most comfortable with.
As I said a couple of days ago, though, you don't have to master every method of metering. Just one or two of the ones that gets you to an exposure that works for you.
*I once photographed for six months with a totally manual camera and no light meter at all, which I documented in an article for Ed Buziak's Darkroom User magazine (U.K.) called "Train Your Brain...To Guess Exposure." It was a fun experience, and taught me a lot about metering and exposure.
I was learning the Zone System at around the same time, and I wrote the article after I noticed that some Zone System photographers actually were quite poor at exposing their large-format sheet film. Although they had the mechanics of the system down pat, they weren't using very good judgement. Poor visualization, one might call that.
**I'll give an example of this last. Let's say you're shooting at ISO 800 and the ideal exposure based on the scene and the interpretation you want to make of it is ƒ/8 at 1/250th. (We'll ignore post-processing remedies here, for the purpose of illustration.) Here are a few of the ways you might use your camera:
- You could spot meter a middle value in the scene and use auto-exposure lock, recompose, and shoot, resulting in exposing at ƒ/8 at 1/250th.
- You could use Manual mode and adjust the dials based on the metering scale in the viewfinder until the camera is set on ƒ/4 at 1/1000th. Since you want more depth of field, you change the aperture to ƒ/8 but stay on the same EV, giving a shutter speed of 1/250th.
- You could use Aperture-priority automatic mode but, based on your knowledge of how the camera meter usually works, add an extra stop of exposure using the exposure compensation (EC) dial, which ends up as, we'll say, ƒ/8 at 1/250th.
- You could use the exposure you've been using consistently for the entire last hour of heavy shooting, that you originally based on a number of careful incident readings with a hand-held meter. That exposure is, you guessed it, ƒ/8 at 1/250th.
- You could use the histogram to "expose to the right" and then move it a little more to the left based on experience, arriving at ƒ/8 at 1/250th.
- You could bracket three exposures with the camera on "P." Later, at your computer, you'll choose the best-looking of the three exposures, which happens to be (you didn't actually notice) ƒ/8 at 1/250th.
- You could be using 100% Kentucky windage—guessing exposure settings based on experience*, totally ignoring any aspect of what the camera's light meter is telling you. The sun is unobstructed but low in the sky so you use your standard daylight exposure plus two stops, which results in, yes, ƒ/8 at 1/250th.
The question: Which of these methods arrived at the best exposure? (It should be obvious that the final exposure is identical in each of our examples, which should make the answer to this question obvious.)
And the follow-up question: which metering method was superior for this particular shot? The answer has to be, none of them. They were, in this case, just different ways of getting to the same end-point. One or another might be preferred by different photographers, who will argue over the superiority of their own preference, saying that it leads to error less often, or is faster, or most reliable, or works well enough, or they've been doing it that way for 30 years, or they just trust the camera and the hell with it, or whatever. But it doesn't really matter which method you chose. In this example.
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Featured Comments from:
Mark L: "The only problems with exposure for me started when I began using digital and film. My black-and-white film I can pretty well guess dead on, and if I'm not sure I err on the side of overexposure, but digital needs to be exposed like slide film to protect the highlights, as these days cameras are good enough to be able to lift the shadows without producing much extra noise. So I have to go out with the mindset for either film or digital and I cannot use both on the same day or my head implodes—easily done these days!"
Mike replies: I have that same problem.
Gary Nylander: "I'm surprised to read that some zone system photographers were quite poor at exposing their large-format sheet film. [Not all, by any means. Just some. And at Photo Techniques, the unofficial house magazine of the Zone System, I believe I saw them all. —Ed.]
"I would say for myself having used the zone system with a large format camera for the past 25 years, using a Pentax 1° spot meter that my exposures are far more consistent and reliable in comparison to the days when I was using a ordinary hand held meter with my view camera, especially shooting landscapes.
"I believe photographers like Edward Weston and many of his contemporaries were known for making exposures with out a light meter, he did some beautiful work just by eyeing the exposure. A few months ago a friend gave me a interesting little booklet called Photographic Exposure Computer, dated 1942. The booklet, about 8x12 cm in size, has a detailed latitude zone map, then a table of light index numbers that correspond to the particular latitude that indicate the proper exposure wherever one might be. I have used it and for most standard lighting situations it works amazingly well—and it fits in my pocket and needs no batteries!"
Joel Bartlett: "And for a follow-on article, may I suggest 'White Balance is an Interpretive Choice.' When I shoot interiors, I have exterior scenes through windows, direct sun, shadow, reflected sun, at least two colors of florescent light, halogen, incandescent, and my strobes. No one spot in the frame is correct; the client just wants me to do the right thing."