What is metering? Metering computes the amount of light that passes through the camera to help you achieve the best exposure for the photograph that you’re taking. For example, if you are on semi automatic modes e.g. Program, Shutter priority, Aperture priority and Auto, the camera does the computation for the exposure triangle and ADJUSTS whatever it can so that you can have a properly exposed photo. In Manual, the metering computes the exposure triangle as well but it DOESN’T ADJUST them. Instead, it shows you a graph to tell you how over exposed or underexposed your photo will be so you have to adjust it by yourself. It’s like the camera is asking you: “Are you sure you want this photo to be underexposed like this?” or maybe : “Are you sure? These settings that you chose will give your subjects a characteristic that medically inclined people usually call “albino-riffic”...I’m just saying... It’s up to you... *cough* dumbass *cough*”
“So what’s the point? Why bother? I’m always in semi automatic mode so why do I need the rest of this lecture? I mean the camera will compute for the proper exposure! Duh?! ” Thanks for the very good question. Basically the metering modes are there to help your camera see which part is the best to meter from and how much. Why? Because not everything around you has an equal amount of light. Some parts are darker, some parts are brighter. So, for example, if you told the camera to focus on something that is dark, it will think that the whole image is dark. If it thinks that the whole image is dark, it will try to overcompensate for that and result in an overexposed image.
The 3 amigos of metering are: MATRIX/EVALUATIVE, CENTER WEIGHTED and SPOT.
Matrix or evaluative metering is the most commonly used because it is the easiest. It “sees” the whole image splits it into parts and then calculates complicated algorithms to expose for it.
Center weighted metering prioritizes the center part of the image(duh?). It’s a bit more accurate because the camera is only considering a small part of the photo.
Spot metering concentrates on a spot. Literally. About 1% of the frame.
How to use them? It’s up to you. It depends on the effect that you’re trying to achieve. I’ll give you an example. Let’s assume that you’re a guy. You're in a beach. You’re lazy so you always shoot in Aperture priority mode. You saw a very sexy lady wearing a very very revealing bikini *gulp* and you suddenly had an inspiration. You imagine a photograph of a silhouette of a lady against a sunset. Nice! Here’s what you should do:
1. Take that creepy smile off of your face.
2. Wipe the drool on your chin.
3. Go up to her and ask if you could take a photo of her.
4. If she says yes, please try your best to remain calm and composed. Calm and composed...
5. Step back and point the camera towards her. Tell her the poses that you’re imagining. NO. Not those poses! I mean the poses for the silhouette shot. *cough*creep*cough*
6. You’re probably perspiring... A lot... You are not thinking properly that’s why you made a mistake of putting your metering to spot. Since your subject is the lady, you’ll probably meter her first. Wrong move. You’ll soon discover that the shot has a very nice exposed body, I mean lady, and an overly exposed sky. I’m sure that photo would still be awesome, but it will only because of the body of the subject and not because of your photography skills.
7. If you use evaluative/matrix, it will try it’s best to keep the subject and the background properly exposed. So again, you won’t have a silhouette because the shot would probably have a balanced foreground with the background. Instead, try using center weighted. But don’t meter off of the girl. You meter the skies so that the sky is properly exposed and then the girl would now be a silhouette. You could use spot metering and meter again for the sky but since you are metering using only a spot, it might be a bit difficult because of inconsistency. If you meter on a darker part of the sky, you would have a totally different photo if you compare it to a lighter part of the sky. Whereas for center weighted, you could just expose at the same part of the horizon over and over until you finish all of your shots.
Warning:
The camera makes mistakes too. It’s because it doesn’t actually see light. Its computations are based on middle gray. Middle gray is like the “standard” of perfect exposure. Blah blah blah. I’m sure you don’t want to read these. But what you should remember is that sometimes, the camera can be a “dumbass” too. It can be fooled when looking at a scene that is mostly white or mostly black. It doesn’t really know what light looks like so if it sees a surface that is white in color, it is fooled into thinking that that white surface is a light source even though it is not. So, if the ambient light in a shot is just right but the scene is mostly white, then the camera might think that the scene is bright. So it will try to underexpose the image to “balance” it out, resulting in an underexposed shot. When the camera sees black surfaces, it thinks that it is seeing a scene that doesn’t have any light. So again, if there is sufficient ambient light, it will still think that you don’t have enough light so it will make the image brighter, resulting in an overexposed shot. So as you can see, telling the camera where to point and what mode of metering to use is crucial to having a perfectly exposed shot. Here are some examples:
This photo is shot using evaluative/matrix metering. As you can see, it is a bit underexposed. But only a bit. Why? Because there are more white surfaces than black. So the camera thought there's too much light and it darkened the shot a bit.
Now in this photo, I used center weighted. It's overexposed. Because the center weighted metered the mostly the black part of my cellphone and only a bit of the white table. Since the camera mostly saw the black part of the cellphone, it got fooled into thinking that the photo needs extra light. That is why it over exposed it.
Now in this photo, it is waay over exposed. I used spot metering in this one and metered only the black part of the cellphone.
Now, in this photo, I used center weighted again but this time, I took the liberty of placing it in a different place so that it has almost equal amount of white table, silver keypad and black lcd of the cellphone. The result is a properly exposed image.
So there you go! Now you know metering. Try to practice it to get a feel for what metering mode to use in a given situation. It will help you tremendously. See you next time!
BUT WAIT! THERE'S MORE!
Since I was gone for a long time, I'd like to give you a bit of a bonus tip. Here's my technique. Others may find it complicated, others might think it's convenient so it's up to you if you want to use it. You may consult your manual if you get confused with these settings:
1. Set your camera so that when you half press the shutter, it autofocuses.
2. Set your AE-L/AF-L (nikon) to Auto exposure lock only. For Canons, I'm not sure but I think the button that you should be looking for is the Star or Asterisk button. This button is your Auto exposure lock.
3. Set your focus to Single point.
After you've done that, here's what you can now do:
1. Put your subject in the center of your viewfinder. Focus on it by pressing the shutter button halfway. Don't let go of the button.
2. Meter where you want to meter. If you're using the spot and center weighted mode, you can point to wherever you like. Then press the AE-L/AF-L (nikon) or Star or Asterisk button (canon) to lock your exposure. However, if you are using Evaluative/Matrix mode, disregard this and proceed directly to step 3.
3. You can now compose your shot. After composing, press the shutter button fully.
"Why do I need to do these steps?" So you can control everything. This way, you can focus on a subject, and then move around to meter where you want to meter.
-Autofocus sometimes focuses on the wrong thing. But with Single point focus, just point it at where you want it to. You can recompose the shot while maintaining focus as long as you don't let go of the button.
-Exposure lock is very helpful because once you lock it in a proper part of the camera, you can recompose the shot but still get the the proper exposure until you let go of the button.
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