What Is the Difference Between Metering and Exposure Compensation?
Last week I was thinking about a very specific kind of metering that is an option on my Ricoh GR 3. It is called Highlight weighted metering and it joins the other three, more traditional metering choices which are Multi segment weighted, Center weighted and Spot metering. In researching Highlight weighted metering, I came across the question, “Do you understand the difference between metering in a camera and exposure compensation?” Well, I more or less understand metering, although I can be a little fuzzy about the ins and outs of specific metering choices. I also understand exposure compensation. However, I don’t think I have ever put the two concepts side by side to explore their relationship to each other.
Photos brought to you by the color Yellow.
Metering is how your camera delivers, through changes in shutter speed and aperture, the best exposure based on the ISO that is set and the available light. Now there is some camera guesswork in this, because in-camera meters can only measure the light that is reflected from an object. The problem is that real world objects reflect different amounts of incident light. In order for a camera to evaluate the incidence of light, it has to measure against a standard. That standard is 18% middle grey, although the standard varies somewhat between cameras. Thus, when a camera meters, it sets the exposure so that the exposure would be appropriate for the luminance of light coming from an object that is middle gray. Now this works pretty well, if the scene you are metering has an even spread of light and dark objects. They all average out to nice middle grey. It is not so good when the tones are predominantly light or dark. Roughly what would happen if you were taking a picture of a polar bear in snow, is that your camera would register the bright light and expose to make the scene a middle grey. You would have a greyed-out snow which has actually been overexposed. Or, if you were taking a picture of a black bear in a dark forest, the camera would again try to return a middle grey image and end up underexposing the dark image, so you would have a greyed out black bear.
If you are teaching a beginner photography class, or just want to have some photography fun, you can run a little experiment to see just how true this is. Take a picture of a middle gray card, a black card and a white card with nothing else in the picture. The challenge here, by the way, is getting the camera to focus. That will totally flummox new photographers and maybe some experienced photographers. For beginners, that is a lesson in itself. In any case, your resulting three images will be shockingly similar, essentially a middle grey.
This is where exposure compensation comes to the rescue. Exposure Compensation is what you can do to override the exposure decisions of the metering process. Let me hasten to add that Exposure Compensation is only available if the camera is actually making metering decisions which is when it is in an automatic or partially automatic mode. Those modes are Automatic (all decisions are made by the camera), Program mode (the ISO is set), Shutter Priority (ISO or Automatic ISO and Shutter Speed are set, Aperture varies) and Aperture Priority (ISO or Automatic ISO and Aperture are set, Shutter Speed varies.) If you are in Manual, the camera does not make metering decisions, that is left up to you. You cannot use Exposure Compensation in the Manual Mode. That always surprises me and frustrates me, which certainly indicates I do not have a complete handle on shooting in the Manual Mode.
The use of Exposure Compensation is not necessarily intuitive. Let’s go back to that polar bear in a snowy scene. When you take the picture, instead of getting crisp whites and highlights, you may well get dingy grey as the camera exposes for middle grey. The camera has to underexpose to take a white to a grey. To compensate for it, you have to overexpose the picture. Tell me that isn’t just like all matter’s photography. If you have a really light scene you may have to compensate with overexposure. Similarly, if you have a really dark scene you may have to compensate with underexposure.
Of course, we can use Exposure Compensation for creative reasons rather than to simply correct a camera metering decision.
Now for a little color theory.
Yellow
Yellow is the most visible color at night. This is why taxi cabs are often yellow. In daylight the most visible color is 550 nanometers, which is a color between yellow and green. For safety reasons, joggers often wear yellow green fluorescent vests. Note to parents: babies cry more in yellow rooms.
Yellow is associated with:
Optimism, energy, prosperity
Joy, happiness, friendship
Follow the yellow brick road.
Tie a yellow ribbon around the old oak tree.
The flip side:
Jealousy, betrayal, cowardice
Illness
Warning, danger
Yellow belly.
Yellow streak.