Metering

[DianaS]

Ok, this is probably a dumb question but I'm rather newto photography and I'm confused how to meter to get the right exposure. Do i need to be in manual or any setting? I have a Canon T2i. I know it has the four meter modes but am just confused. Any help would be GREATLY appreciated!

[homank76]

What mode do you usually shoot in? Your camera should have a meter on it and you line it up in the middle. You do this by adjusting the ISO, shutter speed and aperture. Also, how do you meter, spot, matrix, center?

[DianaS]

Originally Posted by homank76

What mode do you usually shoot in? Your camera should have a meter on it and you line it up in the middle. You do this by adjusting the ISO, shutter speed and aperture.

I guess I mainly shoot in Av. but will dabble in TV, P (sometimes) and haven't really tried M because I don't feel comfortable enough yet I guess. But is the Meter the -2..1..0..+1..2? if so the line is always in the middle. But when you meter, doesn't that kind of tell you what your setting should be at or no? See... I'm so lost. But trying!

Originally Posted by homank76

Also, how do you meter, spot, matrix, center?

and... huh!? lol. I don't understand that! (That's how new I am to this!)

Thanks for the input!!

[brianxlt]

Your camera has four meter modes and can be used many different ways. You can use the spot meter in a shaded/shadow area and then on a bright area of the image to get a well lite image. you can use the evaluated meter to do almost the same thing without moving/adjusting the camera.
Best way to see what they do and how they affect an image is to - find a sunny and shaded area outside, set your camera on (M) manual, set shutter speed and aperture then move through each meter setting taking an image at each setting. after reviewing the images you will notice slight differences in the exposure of each. This way you can determine what meter setting will be best for any given lighting setup.

[nickbedford]

The Mode dial on your DSLR gives a lot of different options to choose from, but for most photographers, the three that are used are the Tv, Av and M modes.

Tv stands for Time Value. This mode allows you to restrict the shutter speed to a particular setting (such as 1/100th of a second) and the camera will then meter the scene and choose an ISO and aperture combination that will produce a correct exposure. If your ISO is set to a particular speed (such as ISO 100), only the aperture value will be automatically set.

Av stands for Aperture Value. This mode allows you to restrict the aperture to a particular ratio (such as F/2.8) and the camera will then meter the scene and choose a shutter speed and ISO combination that will produce a correct exposure. Again, if the ISO is set to a specific value, this limits the camera to only choosing the shutter speed for you.

M stands for Manual. This mode has limited or no automation, and typically, the only setting that can be set to automatic is the ISO speed. In this mode, you must select both the shutter speed, aperture and ISO speed to produce a correct exposure (obviously correct is open to interpretation or depending on how you want to expose your scene).

To meter the scene, you need to get a handle on what each setting does, but the needle in your exposure ruler gives you the current exposure based on the exposure settings as well as the metering mode.

The most common metering modes are Spot, Center Weighted Average, Evaluative (or Matrix) and Average.

Spot uses a single point to meter from. If you want to meter the exposure for someone's face, point this spot metering point at their face.

Center Weight Average takes a center biased average of the whole frame.

Average takes a measurement across the entire frame.

Evaluative (Matrix) uses algorithms to "evaluate" the correct exposure using a variety of different metering points and decisions. Certain cameras will have varying degrees of success in this mode, and it is the most complex metering mode. Improvements are constantly being made to this mode through use of colour metering technology (not just luminance) and increased density and increased complexity of the programming.

[inkista]

Originally Posted by DianaS

I guess I mainly shoot in Av. but will dabble in TV, P (sometimes) and haven't really tried M because I don't feel comfortable enough yet I guess. But is the Meter the -2..1..0..+1..2? if so the line is always in the middle. But when you meter, doesn't that kind of tell you what your setting should be at or no? See... I'm so lost. But trying!

This is because you're in an automated mode.

Yes the -2..1..0..+1..2 is kinda/sorta the meter readout.

Your camera's sensor is basically used to measure the amount of light that's coming in. Then, if you're in an automated exposure mode, the camera will then adjust exposure settings to what it thinks will give you the optimum exposure (0 on the scale). That's why it always looks like the needle's at 0.

However, because the autoexposure system might not be 100% correct in where the exposure should lie, you can adjust the exposure settings up or down on the meter readout. This is known as EC or exposure compensation. The scale is marked off in EV (exposure values), or "stops". A stop is the doubling of the light in the scene. So going from -1EV to 0 is like doubling your ISO. The mode you pick determines which setting gets moved around. In the case of Av, it's the shutter speed that switches, based on the metering.

If you were shooting in M mode, the needle would be bopping about all over the scale, depending on how much light was coming through the lens, and it would shift about as you adjusted the exposure settings. Putting the needle on 0 is what the automated modes would do, and is likely to get you into the ballpark of a correct exposure, but it's not always going to be right.

and... huh!? lol. I don't understand that! (That's how new I am to this!)

Shooting modes are one thing. They determine how the settings are adjusted by the autoexposure system in the camera.

Metering modes are another. They determine how the measurement of light is calculated by the autoexposure system. The general modes are things like averaged, evaluative, center-weighted, and spot. Averaged and evaluated basically mean that all the values across the sensor are used. Center-weighted means that all the values are used, but the ones in the center are considered more important. And spot means that only values from a particular area of the sensor are considered.

Generally, the AE system takes those values, comes up with a middle value of some kind (like an average), and then shifts the exposure settings around to make that middle value be "middle gray" in the black-to-white range of the camera.

This works great for most scenes that have an even distribution of dark and light.

But sometimes it doesn't work so great. If you're shooting a snow scene, say, and most of the frame is white, then your middle value is going to be close to white, but the AE system will pull it down to be middle gray, and your shot will be underexposed. Similarly, a night shot, where the frame is mostly white, is going to be overexposed. Or your scene will have a dynamic range bigger than your camera can capture, and you have to choose which end of the exposure is more important to you: the shadows or the highlights.

This is why we have M mode and exposure compensation: so that we can override what the camera mechanically thinks is the right exposure.

You're smarter than the camera. You know what the picture is about. So you know what you want to emphasize, and what makes a good exposure.

[autofocus]

You are really talking about two different aspects of metering.
1) the 3 or 4 metering modes available to use in your camera, and when and why would you choose one over the other. Your choices are: Evaluative/Matrix, Center Weighted, and Spot. I think you need to read your manual where each of these modes will be explained in detail. These are modes that you can choose based on the lighting conditions for your shot.
2) Once you determine the above, controlling your exposure is the second component in metering. This is done by adjusting the various aperture, shutter speed, and ISO settings. These three elements are linked together like cogs on gears. Any change to any one of these will require some adjustment to one or two of the other elements in the exposure triangle. Theoretically, the camera is evaluating the light in the scene, and how it does it is based on the the modes listed above. While looking at the scale in the viewfinder, the center hash mark is what the camera thinks the proper exposure is for the shot. Any adjustment you make with your aperture or shutter will be used to dial in that "proper" exposure into that center hash mark. Any adjustments you make to the left or right of that center hash mark will give you either an underexposed, or overexposed result.

And after all that, there is a third consideration...and that's how YOU read the light, because the camera's meter is only so smart, and often you have interpret the light yourself and outsmart the meter. I hope this is all fairly clear to you

[gturner]

There is some great replies here... but... I am going to be the wise ass to say it....
There is a chapter in the manual dedicated to this. Get you camera, get a subject and play with the camera as per the manual. You will quickly work out what the different metering modes mean.

[graciousness]

I have a feeling that the -2..1..0..+1..2 that you are looking at in the viewfinder is not what you think it is. That's the exposure compensation numbers you are seeing. You use that if you want to adjust the exposure set by the camera (it does not work when you use Manual mode) by +1 or +2 if you want it brighter or -1 or -2 if you want it darker.

Here, this should help you.

Setting exposure compensation of EOS REBEL T2i / EOS 550D