Understanding Your Camera's Internal Light Meter and Metering Modes

Understanding Your Camera's Internal Light Meter and Metering Modes

Understanding the internal light meter of my camera is one of the best skills I've ever learned. It helps me to shoot in fully manual mode, so that I rarely look at the back of my camera. Let me tell you how to get a correctly exposed picture from the first click just by using your camera's internal light meter.

Most of the time I shoot with strobes and then I use a handheld light meter. But when evaluating the ambient exposure, or if I shoot landscapes, I rely on the internal light meter. This saves me time looking at the back of the camera on each click to check exposure, and helps me quickly adjust the basic settings (aperture, shutter speed, ISO) without taking my eye off the viewfinder.

Focal Points

First of all, let's talk shortly about the focus points of your digital camera. These are the points similar to the ones on the above image. You will see them through the viewfinder or in Live View. When you half-press your shutter button, the auto-focus kicks in and judges what focal distance the lens has to use so that the object at this point is in focus. The focus point can be changed from auto to a specific spot. I usually select the center one. The chosen focus point can also be used by the light meter to judge exposure.

What the Light Meter Does

The light meter is an internal function of the camera that gives you a visual indication of how dark or light the image is according to the camera. The light meter is this little thing you see in Live View or through the viewfinder:

Camera light meter indicator

Camera light meter indicator.

Most cameras can change the range of the light meter from -3 to +3. In the example I will use a -2 to +2 indication. When the white cursor is at zero, this means according to camera's internal algorithm, that's the right exposure. A deviation to the left means the image is darker, and if the white cursor is to the right, the image is lighter.

The light meter sees a scene (the picture you point the camera to) as points with different brightness as if the image was all black and white. Each point is evaluated against the camera's zero, which is a 18 percent gray. On the digital monitor that color looks like a 50 percent gray, or the middle shade of gray between black and white:

50% gray on the monitor, 18% gray for the camera

50 percent gray on the monitor, 18 percent gray for the camera.

For each pixel the camera evaluates it checks if its brightness is more or less than this middle gray color. If the majority of pixels are darker than it, the light meter cursor goes to the left. If the majority are lighter, it goes to the right.

Metering Modes

As I said above, the camera evaluates pixels from the scene. Depending on your metering mode camera setting, it may check the area of the whole frame or just a fraction of it. There are two basic metering modes that tell the camera how much of the frame to check. Digital cameras offer more, but once you know the principle, you can decide which one you want to use.

Center Weighted Mode

Whatever this is called in different cameras, it is indicated as a blank rectangle. This mode tells the camera to compare all pixels in the frame to the middle gray and calculate the average brightness. If the average brightness is less than the middle gray the cursor goes to the left, otherwise, to the right.

This mode will give you an overall impression if the scene is well exposed. The problem is it won't tell you if there are way overexposed or way underexposed spots in the frame. That is the reason I do not use that mode when I see very bright or very dark spots in the scene.

Matrix/Center weighted mode

Matrix/Center weighted mode

Partial/Spot Metering Mode

It tells the camera to look at a small area around your current focal point (yes, that's the focus point I told you above). If you place your currently selected focus point to the part of the scene you want to evaluate, the light meter will indicate if it's lighter or darker than the middle gray color. This is the metering mode I usually use because it's more precise.

Spot metering mode

Spot metering mode

How I Evaluate My Exposure in Manual Mode

As I said, I use a spot metering mode. When I first look at the scene, I find the lightest and darkest points.

Finding the lightest and darkest points in the scene

Finding the lightest and darkest points in the scene

I point my current focal point (usually the center one) to each of those areas and see how much the exposure deviates from the zero according to the light meter. I tend to keep the exposure of the lightest and darkest areas between the -2 and +2, if possible. Although your camera manufacturer may tell you the camera offers 10 or more stops of dynamic range, I try to keep the scene in the range of three to four stops (there are four stops between the -2 and +2 indicator).

One stop means the light amount or brightness is twice more or less. When the indicator is at -1, this means there's twice less light than the middle gray point. Two or minus two shows that the light is four times more or less than the middle gray. When shooting in raw file format you can bring back easily about two stops of information later in post. That's why keeping the image within the -2 and +2 range is relatively safe.

If the lightest or darkest parts of the image are outside that range, I change some of my settings (aperture, shutter speed, ISO) so that it makes the image lighter or darker and I find the compromise set of settings where I'm in the safe range.

I do not try to put my darkest or lightest parts in the zero when metering them. That's why they are the "lightest" and the "darkest" areas of the frame. They will always be above or below the zero point. The goal is to see how light and how dark those areas area so the image is in a reasonable exposure range.

Then I press the shutter, and as I'm in manual mode, I take photographs from that point of view without changing my settings anymore.

Know Your Light Meter

When your light meter tells you something is "-2" and it is not that dark, this means you are underexposed. You have to decrease the aperture number or decrease the number indicated by the shutter speed or increase your ISO to make the image brighter. But if the area you point it to is really dark, a value of "-2" may be just right. The same with areas that are indicated as "+2." If that's an area with a white snow, it's perfectly fine to leave it at "+2." That is the correct exposure of the snow. If you point your light meter at the palm of a hand, it should be usually around the zero mark.

Go out, switch into manual mode, and try reading the light meter indicator. Point your camera to bright and dark scenes and train yourself to understand when your exposure is correct without checking the back of your camera. It is quite easy and you will be surprised how soon you can take correctly exposed pictures from the first click.

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18 Comments

Elan Govan's picture

Gosh...I am glad I am not a beginner to photography. Took my wife to a pro cycling event once. She is a very smart woman but hates fiddling with nobs and buttons. So I set the camera up and said " point the camera at the cyclist and press the shutter button".

Had I made time to explain all the above mentioned points, plus adviced her to set the camera to continuous shutter priority mode, increased the ISO to compensate etc etc etc,......we would have very a public row.

Tihomir Lazarov's picture

You are right, it takes time. The good thing about the time-consuming learning curve is, this sifts out those who don't want to become good from those who do.

"Spot... It tells the camera to look at a small area around your current focal point" - In many (many-many, e.g. Canon puts it only on top 1D model) cases it is not your current focal point but center focus point (only).

Tihomir Lazarov's picture

That is correct. That's why I tried to stay away from specific camera models as every manufacture has their own terminology and implementation.

Then it will be "It tells the camera to look at a small area around your current or center focal point"

Tihomir Lazarov's picture

Or better: either around your selected focus point or, as with some camera manufacturers, around the center point.

Elan Govan's picture

Hi Alexander, Canon 40D does have spot metering, but I know the earlier 20D does not.

What a great article!!! I am new to photography and have struggled with understanding my light meter the most. This article really helped. Thank you!!

Tihomir Lazarov's picture

I am happy it helped you.

romain vernede's picture

Even if we talk digital, try to get a lightmeter, and use it incident metering while adding +1,33EV to the reading (playing with shutter speed or aperture)
open your file in lightroom and compare with a file you did with your DSLR's light cell
I beg you won't go back :)

Tihomir Lazarov's picture

Incident reading is quite different from reflective. If you take a light meter that has reflective meter reading functionality, you will get the same results. The reflective reading doesn't only read the "light" but it depends on the texture, its reflectivity, transparency, etc. Those are two completely different readings.

romain vernede's picture

Of course it's different! But with incident reading you skip the usual traps, and see how light "falls" on the scene, never mind texture, tones, colours...

Tihomir Lazarov's picture

I always use a light meter, as I'm working with strobes. I use a light meter when I'm shooting video and I measure the light falling on my subjects. But I mentioned shooting backgrounds and landscapes where you can't measure the light with an incident meter reading, because over a long distance there are many factors that may change the light amount on the subjects. I'm not talking about portraits or close proximity objects here. I'm talking about the general case. For close objects, that you can reach, using an indident reading is the way to go ALTHOUGH some textures with certain reflectivity and transparency the reflective reading may be more suitable. That's why skins of different people do not look the same when you use the same settings.

Robert Nurse's picture

Very helpful article. But, I have a question. Are you basing these extreme points (+/-2 stops) on your midtone reading? In the photograph of the field, what part of the scene did you meter as your midtone?

Tihomir Lazarov's picture

Yes, the extreme points are based on the midtone reading.

In this photograph I would use the farthest mountains or the lit green part of the trees as a midtone. From that I will check if the lightest and darkest parts are within the range.

Sometimes there are no suitable midtones and in this case I check only the extremes, especially when photographing clouds (I have a database with sunsets and clouds I use for composites). With them, I check the lightest part of the cloud and it is usually around the +2 which is similar to photographing snow.

michael bogert's picture

Thanks for the article. I hadn't ever noticed the meter working while taking pics before. I immediately picked up my camera, pointed it out the window and watched how the meter changed as I pointed to different places. I'm going to bet I start getting better exposed pics starting right now! Thanks again!

Tihomir Lazarov's picture

You're welcome Michael. Thanks for your feedback! I have friends who have been told that shooting in manual mode with the light meter is only "for pros", and it's "very hard." They are not professionals and now say it's way better and easier to work with camera's light meter than they've been told.

Studio 403's picture

Call it meter dummy from hell. I have this meter from a name brand company. when ever I use it, and I set my camera to the settings outdoor, UGG, I cannot get it to give me the proper exposure.....HELP!!!. I am heading to my basement window and jump, if I can draw a crowd.

I have watch more videos on this unit.....no success.