Metering: Which Setting Should I Use and When?

We all know the rule of thumb to shoot an outdoor portrait in the shade –  to avoid harsh lighting and shadows. But a common problem occurs if you have any sunny areas in your frame: a properly exposed sunny background but an overexposed subject. I’m sure you’ve all seen it before: a subject under a shady tree that looks dark while the sky behind the subject is the right shade of blue (if only you were going for a portrait of the sky, but unfortunately, you weren’t). This problem is easily remedied with an understanding of your in camera light meter.

There are four types of metering generally found in a digital SLR camera:

• evaluative
• center-weighted average
• partial
• spot

The two extremes are evaluative and spot. The other two are just somewhere between those evaluative and spot. Check your manual to see how to change the type you’re using.

Here’s what you need to know:

Evaluative

This is a general-purpose metering mode. The camera sets the exposure automatically to suit the scene – the whole scene. Many photographers use this most the time.

Use it

• in a hurry
• when the lighting is consistent across your scene
• to photograph landscapes
• when you want to every detail to be visible – nothing too dark and no whites blown out.

This metering mode (evaluative) is usually the culprit in a poorly exposed photo. That’s because your camera is averaging  the entire scene in the viewfinder (the shady and  the sunny spots) so you end up with a scene that is bland and exposed to middle gray.

Spot

This is for metering a specific spot of the scene. The metering is weighted at the center.

Use it

• when someone or something is backlit
• to get more exact metering for the part of the scene you want exposed most correctly (in a portrait, this would be the face)
• when being creative – you want the sky properly exposed but leaving the ground dark or vice versa.

I am in the minority, but I use spot metering pretty much all the time. I prefer to purposefully choose the most important part of my scene to expose. I aim my camera there, adjust my settings according to the in-camera light meter reading, and then snap away. Then it doesn’t matter if I’m shooting in the shade and some sunlight is in the background because I’m metering off the subject’s skin.

In a backlit situation, you will end up with a blown out background, but that’s generally preferable to the alternative — not seeing your subject because it’s too dark.

If you want both the background and your subject properly exposed, use your spot meter mode to determine how to properly expose the sky, and then light up your subject with a flash.

What if you’re not sure which to use?

Then go in between evaluative and spot with one of the following:

Center-weighted average

This metering mode is weighted at center and then averaged for entire scene. Basically, it’s evaluative, but it takes into account what’s in the center more than the rest of the scene when letting you know if your image is properly exposed or not.

Use it

• when you care more about a subject than a scene, but still want the scene exposed so it’s not blown or losing too much detail.

This would be a good choice for a person in front of the ocean or a scene with the sunset behind them (unless you’re using a flash – then you should use spot metering).

Partial

Partial metering covers more of the viewfinder area at the center than spot metering.

Use it

• when you want to use more of the scene to get your exposure reading
• in certain backlit situations, like if you don’t want your subjects too dark, but the lighting on the subjects is uneven so you want an average.

To understand the advantage of partial metering, consider this: you’re creating a portrait and you want the skin and eyes properly exposed, but you get different readings for each depending where you point the “spot”. Choose partial and you’ll get an average of both without considering the rest of the scene you don’t care about exposing properly.

Note, all these are for when you’re in a hurry and want “close enough.” To get the most accurate exposure settings, you should meter something that is 18% or middle-gray. For best results use a gray card or a target. You can meter off other objects, but the closer to middle-gray, the more accurate your exposure reading will be.

In all cases, check your histogram to make sure you aren’t blowing any whites.

Source : http://www.spectrumphotographytips.com