Last year I wrote a simplified explanation of in-camera metering. If you know nothing about your camera’s internal light meter, please start there. If you need a refresher, head over there to catch up. It’s okay, I’ll wait… 
In my first metering post, I explained that your camera will meter the light in your viewfinder and show you if your settings will over-, under- or properly expose that image. You adjust your shutter speed, aperture, or ISO until the tick marks level out.
But… then I get questions like this:
“My in-camera meter was leveled to zero, but when I got home all my photos were dark and under-exposed!”
So now we need to get more specific. Most dSLRs offer several different options for metering light in your image. The results you get will vary based on which metering mode you choose.
Meter Modes Common to dSLRs
matrix metering / evaluative metering: metering for the sum of the image, and the strength of light in many areas in the viewfinder. Nikon uses 1005 pixel-points to measure lots of areas and compares it to a database of 1000s of images to average the light and determine the exposure. Canon uses the sum of the image with an emphasis on the focal point.
center-weighted metering: uses the center focal point to measure the amount of light needed to best expose that part of the image. The size of measurement, often made in millimeters can be set in the menu of your camera. You can choose a broader area to meter, or make the meter a very fine point – like 8mm diameter – which to measure. It will disregard the strength of light in other parts of the image and expose only for the part in the center. If your subject is not in the center of your image, you will need to measure, create your settings, then recompose the image.
spot metering: a precise, small area of light measurement, used to target the strength of light on a specific part of the image. On most dSLRs it measures exposure where you place the focal point. There is no need to focus and recompose (which is bad habit if you work in shallow apertures!). Spot metering requires you to know and understand Ansel Adams’ Zone System.
Come back tomorrow to learn more about these metering modes, the pros and cons to each one, and why I chose the metering mode I use.
Can’t wait till tomorrow, this is one area that I find confusing and haven’t practiced enough.
Many people will be glad you are explaining this one. I learned this the hard way last year – lots of mitakes and practice. Then I went to an awesome workshop where we learned to tell our camera what to think about the light all around. I have never seen the light the same
Thanks for all you share Darcy!
My gosh, you are one brilliant chick! How on earth did you ever learn all this stuff??? *impressed*
So thankful you are writing about this. I definitely get confused about this and can’t wait until tomorrow!
You teach me so much,
*Thank you*
OK…this is finally making sense! You are the BEST teacher ever. Thanks so very much Darcy. Which one do you use most?
I have a canon rebel T2i and you cannot move the spot meter location to any other focus point (it’s a circle in the middle that is used for spot metering.) I use the AE lock unless what I spot meter from is in the center of the frame, which is kind of a pain when you want to use your thumb to change your focus point.
Hey Darcy – what do you mean by this on center-metering?
“you will need to measure, create your settings, then recompose the image.”
Metering is different than focusing. When you are first trying to meter the light, you will move the focal point to what you’re metering – let’s say the sky. You point your camera to the sky and using the zone system, you figure out where you need your internal light meter’s tick marks need to be.
Now let’s say skin. You walk up very close to your subject and fill the view finder with the skin and meter that to the correct exposure. As long as the lighting stays the same you won’t need to re-meter. You can then step back and compose the image as you’d like… and shoot, ignoring your meter which may now be assessing more than just your subject. When your lighting changes, you’ll need to adjust your exposure accordingly.
Hope that clarifies!