Camera Exposure & Metering Modes

KristinaW

Active Member
  • #1
Every time you half press your camera's shutter button, the camera "meters" your scene. Metering is when the camera's light sensor assesses the given light that's in front of it. Sometimes, it's very easy to measure the light because there's not much contrast in the area, but sometimes the camera has difficulty because there are bright spots as well as dark areas where you'd like to take your photograph. Because the camera is only able to capture an average of the light in any given zone, its exposure result may not fit your needs. Your resulting images may be either over exposed or under exposed. Luckily, there are additional tools contained within a camera that can assist you with acquiring the perfect exposure. I'll explain all this much more clearly below.

Let's work through a quick example to clarify what I just attempted to explain above. By the time you're finished reading the paragraph, you'll likely understand how difficult a camera's job at getting the right exposure truly is. Okay, let's say that you point your camera straight at a wall that's painted half black and half white. One side is super dark and the other is super light. If you were to meter the scene, what type of exposure would your camera choose to return you? If the camera says, "Hey, the black part of the wall is really dark. I better increase the exposure to compensate for that," you're going to end up with a photograph that's way too bright on the white side. Sure, the black side will look good, but the white side will be useless. If the camera chooses to reduce the exposure because the white side is so bright, the resulting photo will be great on the white side, but ultra dark on the black side. So what's a camera to do? And on top of that, how is the camera supposed to know what you'd like it to do? It's almost a no-win situation for the camera.

Average Reflectivity

There's this thing in the photography world that's called average reflectivity. When a scene's lighting, all combined, is 18% grey, it's said to be of average reflectivity. Light bounces off the surfaces of objects in any given scene and a camera's light meter absorbs that light. If you were to point your camera at a wall that's emitting 18% grey, your camera would have no problems metering the scene correctly. But when you point your camera at the corner of a room that's got a desk and a lamp in it, how is the camera to know whether it should brighten the really dark area under the desk or tone down and darken the brightness of the light bulb inside the lamp? It can't have it both ways, but as I said above, there are things we can do to help the camera out.

And just to go back to the example I gave directly above, if the camera chose to brighten the dark area under the desk, the lamp light would cause an overexposed image. If the camera chose to darken the light coming from the lamp, the dark area under the desk would cause an underexposed image. I'm sure you've seen a picture of someone who's standing in front of the sun. The camera meters the scene in such a way as to darken the sun somewhat, but inadvertently blacks out the person completely. They end up looking like a silhouette. This is the same kind of thing that happens when the camera tries to darken the scene because of the light coming from the lamp. It completely blacks out the darker area under the desk.

Metering Modes

There are a few different settings that we can take advantage of to steal some control back from the camera. By default, the camera will, as I said above, average all the light in the scene, but by changing a setting or two, we can isolate where in the scene the camera looks for light. This is super helpful in very diverse areas. The settings I'm referring to here are called metering modes and there are commonly three of them.

Evaluative/Matrix Metering: With this setting, the camera divides the entire scene up into a grid that's got equally size partitions. Each of the partitions is equally weighted and all of them are averaged for one common exposure. This is the setting I was referring to above. It's usually set by default.

Center-Weighted Metering: If you were to draw a circle at the center of your scene that covers about 60%-80% of the area and then weigh that circle heavily in regards to the light that's in there, you'd have a center-weighted metering setup. The outer edges of the scene are used when metering as well, but they aren't taken into consideration nearly as much as the center portion is.

Spot Metering: Similar to above, but this type of metering only covers 1%-5% of the center of the scene. This is like a laser focus on a very specific area's light that you'd like to take into account. While the spot is generally locked to the center of the scene, some cameras do offer the ability to lock the spot metering location to a focus point. That's very handy because you can move it around.

Exposure Compensation

As good as the above setting options are, they sometimes just can't handle a scene that's got lots of bright and dark areas. Sometimes, it's better to take full control and tell the camera exactly what you'd like the exposure to be. In times like these, it's best to use your camera's exposure compensation feature. Basically, this feature allows you to brighten or darken your exposure by what's referred to as stops. I used this feature all the time and it's super helpful. To read more on it, please click through to a different post on the subject.

How do you handle exposure when you're out photographing? Do you have any special tips or tricks you'd like to share? If so, please do down below. Thanks!

PS - If you have any questions, please ask them down below too.
 
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