Objective: to learn what a light meter is and how to use it to improve your photographs.

This past Saturday I had a class at my studio.  It was for people who wanted to learn how to use their digital SLR and take better photographs of their family.  We had a great time and everyone seemed to leave with new ideas and a better understanding of what their camera is doing.  Some of the questions that came up a few times were, what is my light meter?  Where is my light meter and what is it doing?  So today we're going to talk about your light meter.

Almost every digital SLR camera on the market these days has a light meter in it.  The light meter tells the camera how much light is in a scene, which then helps the camera decide what settings to use to get the best image.  You will find this inside the camera when you look through the lens and/or on your LCD display and/or on top or in back of your camera.  It should have a center mark or line with lines at each side.  There should be numbers like -1 and -2 on one side and +1 and +2 on the other side.  If you are in manual mode or one of the semi-auto modes (like aperture priority or shutter speed priority) the little center dash should move back and forth when you adjust the dial that changes the f-stop or shutter speed.  If you are underexposed (too little light) the moving line will be on the minus side.  If you are over exposed (too much light) it will be on the plus side.

The +1 or -1 means 1 stop over or under exposed.  One stop is either one f-stop or one shutter speed depending on which of those you are moving.

Your camera has various metering modes.  Usually they will be partial or spot metering, Evaluative (Canon) or Matrix (Nikon) metering or center weighted.

Evaluative or Matrix:  This mode takes a sample light reading from a set amount of points in the scene and creates an average between them.  This is good for most situations where the scene is balanced and the light is not extreme on both ends (really bright and really dark).

Partial or Spot:  This mode takes a sample light reading from a spot (the center of your frame) and everything else is ignored.

Center-weighted:  In this mode the camera takes an average like in Evaluative but it places more "weight" on what is happening in the center of the frame when it calculates your exposure.

So, how does the meter know what to expose the scene as?  What is the camera metering exactly?  It is taking a reading of how much light is being reflected off of your subject and back towards the camera.  It takes the readings and tries to make your whole scene look like this:

That is what is called an 18% gray card.  Cameras don't know that you are photographing a person or a dog or a mountain.  The light meter only reads light.  It takes all of those points and creates an average that looks like this color gray.  Many photographers carry these cards in their bags and meter off of them to get the precise reading.

Why is all this important?

If you are taking a picture of a snow covered meadow, does it look like the color of that card?  How about someone with very dark skin, a black cat or a white wedding dress?  In most situations the gray average is fine but in certain circumstances you may want to over or under expose a little to brighten a white or darken a black.

Here are some examples of times when you may want to overexpose:

The subject is dark compared to the background
Snow or white
When the day is very bright and your subject is in the shadow 

Here are some examples of times when you may want to underexpose:

The subject is really light compared to the background
When you want to create a silhouette
A very dark subject- black animals, black fabrics, dark skin, black suit, etc.

When would you change your metering mode from Evaluative or Matrix to something like Spot?  This is something that I do often.  I will give you an example.  As always, these images are un-retouched and straight out of the camera.

Example 1- using the Evaluative metering mode:

Not great...you have no idea what he's looking at.  This is because the inside is so dark and the outside is bright.  Cameras have a real hard time with this wide of a range.  Now, here's the image again but in spot metering mode.  I metered the part of the scene that I wanted to look as it did.  In this case it was the background.  This is important!  In this type of situation, the spot needs be looking at the part of the scene that you want to be reflected accurately or as it is.  This technique is especially helpful when trying to achieve a silhouette or when your subject is strongly lit from behind.

Aha!  Now we can see what he's looking at!  Water!  Boats!  Much better right?  In the end this one ended up being my favorite.

This week, your homework is to experiment with your metering modes.  Read your manual and learn how to change the setting.  Try and find a scene like the one above.  Experiment with silhouettes and back lit subjects.  I would love to see your experiments.  Please post links to your test images in the comments section. 

Happy Monday!