The light meter:How to take a correct exposure | Camera Basics 101

Previously we talked about why turning your camera setting from Auto to Manual is the first step to taking beautiful pictures.

And you now know that you need the right combination of three things: aperture, speed, and ISO to take a correct exposure. Can’t remember what those three things are? Just click here.  We will be talking about each of these three more in depth in the next weeks. And you will be given some fun homework to get you jump started in learning your camera one step at a time! But before we move on, first we need to talk about the light meter within your camera.

What is the light meter?

The light meter is a device in your camera that knows your aperture, speed, and ISO settings at all times. Your light meter will tell you if the settings you chose will give you a correct exposure!

Where is the light meter?

If you look through your viewfinder (like you are going to take a picture), you will see something that looks similar to this:

That little ticker line with the plus and minus signs on opposing ends, that is your light meter…it’s your new best friend!

The light meter will tell you if your picture you are about to take will be a correct exposure or if it will be under or overexposed.


Let’s step away from the camera for a second and think about it this way… (Bryan Peterson explains it all so well in his book: Understanding Exposure)

 Imagine your lens opening (aperture), is open to lets say f /11, is the same diameter as your kitchen faucet opening.  Now imagine that your faucet handle is your shutter speed dial and that waiting in the sink below are 200 worker bees, each with an empty bucket. The water coming through the faucet will be the light. It’s the job of the camera’s light meter to indicate how long the faucet stays open to fill up all the buckets of the waiting worker bees below.  The light meter knows that there are 200 worker bees and that the opening of the faucet is f /11. So with this information, the camera’s light meter can now tell you how long to leave the faucet open, and assuming you turn on the faucet for this correctly indicated amount of time, you will record a correct exposure.  In effect, each worker bee’s bucket is filled with the exact amount of water necessary to record a correct photographic exposure.

What happens if the water (the light) is allowed to flow longer than the meter says? The buckets become overfilled with water (too much light). In photographic terms, this is called an overexposure.  If you’ve ever taken an overexposed image, you’ve undoubtedly commented that the colors look “washed out.” Conversely, what happens if the water (the light) coming through the faucet is not allowed to flow as long as the light meter says? The buckets get but a few drops (not enough light). In photographic terms this is called underexposure.  If you have ever taken and underexposed photo, you’ve found yourself saying, “ It’s hard to see what’s there, since it’s so dark.”

 So your light meter will help you record a correct exposure. If we look back at the image above, you will notice that a correctly exposed picture is indicated when the dots below the ticker are right in the middle (underneath the “O”) between the plus and minus signs.

So far it is pretty simple, all you have to do is find a combination of aperture + shutter speed +ISO= that equals a correct exposure on your light meter.  That being said is it safe to say that you can record a perfect exposure every time? Not quite, but you are a whole lot closer…

Now it is time to talk about how to choose the best aperture, speed, and ISO for each picture opportunity. So you not only have a correct exposure, but the perfect exposure.


Next week: How to Choose the Best Aperture


P.S. Your viewfinder and light meter may look a little different than the image above. If so and you are having trouble, your camera manual will be of great help :)




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