Metering.

[Andreal]

Ok, so I hear people talking about metering and exposure alot. Now I understand exposure fine (well I understand shutter speed and apeture well enough, I'll learn more about ISO and stuff when I'm more comfortable with it ), im a little confused about metering though. I understand from reading the manual that it has something to do with how the camera sets exposure (is it only used in auto modes then?) and I know that my camera can be set to three different metering methods (3d Matrix, Center-weighted and Spot). I guess I just mostly want to know when to use each type, at the moment i dont really understand what it is and when it should be changed.

Thanks!

 

[panocho]

Hi!
metering will work at any mode, be it auto (programs, aperture priority and shutter speed priority) or manual. The camera meters the light with a built-in metering system so that you or the camera alone can have the correct exposure value.

There are three different metering systems, and your camera has the three. You choose one depending on the situation you're shooting and your personal preferences. Some people, for example, will always shoot with center-weighted, since that's the one they learned to use (older cameras used to have this one as the only metering option); others never switch from matrix or even spot.

Matrix means that the camera calculates the correct exposure value metering different areas of the image and then, using pre-programed settings, it "guesses" the situation and selects the EV that should have all the scene right.

Center weighted will meter around 60-70% in the center of the image (normally, the circle that you see in the finder) and the 40-30% in the rest. The EV is calculated according to those parameters.

Spot will meter exclusively an area of about only 3% of the whole image. It used to be the center of the image (another little circle in the finder will show it), but in modern cameras it can change according to what you're focusing (the spot moves to the AF selected area).

In order to use spot metering you should know a little about how metering light works; besides, it normally is used only in situations difficult to calculate the EV with the other systems. So I suggest you start practising with matrix and center-weighted. Soon you'll start to prefer one over the other, probably, or just learn to adapt to situations.

If you have a digital, I would suggest taking the same picture at the same moment using consecutively the three modes to see how metering can change. A complicated light situation would help to see the differences (they can be huge!)

Good luck!

 

[Digital Matt]

Regardless of the type of metering mode, it's imperative that you learn what the meter is trying to do. It can only suggest settings to render the scene to a middle grey, or 18% grey. If you don't know what that is, buy a grey card.

This is important to know, because if you are metering snow, and you follow the meter recommendation, you'll get 18% grey snow. If you are photographing a black dog, you'll get an 18% grey dog. The meter only gives a recommendation, and you have to adjust your settings to overexpose or underexpose, based on your subject

 

[Mike_E]

Hi Andreal, as to the why of it, the camera can only reproduce a certain range of light to darkness and tries to adjust itself -or get you to adjust it- to the middle of the range which is about 18% grey.

As to the different modes, most of the time a Nikon (did I remember right?) works very well in matrix mode. In some of the cameras using an older lens without the cpu, the camera cant meter in Matrix and will use center weighted which is a trimmed down version of matrix.

Spot metering on the other hand is a different beast. You should only use this when you want your subject exposed in a certain way and are mostly unconcerned about the rest of the photo. I would suggest that if you use spot metering that you only use manual mode.

Here is an idea for you. Go out today and look for high contrast shots (where there is a large difference in shadow and light- very bright and dark) and practice using your spot meter. Move the exposure up and down with the shutter speed as you don't want too many things going on at once.

good luck

mike

 

[Andreal]

Ah thanks guys! This has really helped my understanding, I will go out and test it all tomorrow (its 2am here atm ). I think my original trouble in understanding came from thinking that the exposure was set from shutter speed and apeture and that you could offset that by the EV steps, if im not mistaken the EV steps are actually offsetting the metering which is the cameras "guess" at how much the image should be exposed?

 

[Mike_E]

You could think of it that way. Another way to think of EV steps is to think of adjusting the meter to read different percents of grey. Say plus 1 EV is telling the meter to read 16% grey instead of 18% (I have no Idea what the percentages are but you see the point I hope).

mike