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Metering?
Can someone explain metering to me? I keep seeing references to metering off one part of the frame, then recomposing, etc. As a beginner, I frame my shot, then make adjustments (usually to shutter speed) until the exposure looks correct on the scale at the bottom of the viewfinder...

Comments (12)

You may want to readhttp://www.dpreview.com/learn/?/Glossary/Exposure/Metering_01.htm.

To put it somewhat succinctly, metering is the act of measuring the brightness of some part of the scene, so that one can determine an appropriate exposure value for it..

'Some part' may be 2-3% of the image (spot metering), it might involve the whole scene with some weighting and computation to boil things down to -one- number (perhaps an averaging process, perhaps a mode intended to take into account some extrema so as not blow highlights or not to lose shadow detail, and so forth)...

Comment #1

Sounds to me like you are doing everything right. I think what you were referring to was use of exposure lock in situations where the lighting is difficult (e.g., a strong backlight). In these instances, you can use spot or partial metering (for the latter, zoom in before metering, then zoom back out) and meter on your subject by pushing the exposure lock button (labelled *). Then recompose, focus as you normally would, and take the photo. This is explained in deteil in Gary Friedman's ebook "The Complete Guide to Canon's Digital Rebels.".

Jerryhttp://jchoate.zenfolio.com/..

Comment #2

The previous poster has given a common example. Imagine you are taking a picture outside and there is some bright sky in the background. If you compose the shot as you want it, the meter will see some of the bright sky and give a shorter exposure. the result is that the part of the picture you actually want - e.g. the person or the building in the foreground - will be underexposed..

A simple remedy for this is to point the camera down so that there is no sky in the viewfinder and take a meter reading off the ground which will be about right. Hold down the exposure-lock button (or half-press the shutter to lock exposure and focus). then re-frame the shot and take the picture; the exposure will now be (more) correct for the foreground subject..

This is about the simplest example of what can be difficult in unusual lighting conditions, but I hope it illustrates the point..

Best wishesMike..

Comment #3

Thanks for the replies. A follow up question: what's the purpose of locking the exposure? Using the above example, say that I adjust the settings in the camera for a proper exposure while framing only the ground. When I reframe, the camera will now tell me that I don't have a proper exposure, but I already know that's the exposure I want. So why do I have to lock the exposure? Is it just so the camera "agrees" with my exposure choice? Am I missing something?..

Comment #4

Teris wrote:So why do I have to lock the exposure? Is it just so the camera "agrees"with my exposure choice? Am I missing something?.

You lock the exposure, so when you re-compose, the bright sky does not cause the meter to shorten your exposure, which would cause underexposure...

Comment #5

Mike703 wrote:.

The previous poster has given a common example. Imagine you aretaking a picture outside and there is some bright sky in thebackground. If you compose the shot as you want it, the meter willsee some of the bright sky and give a shorter exposure. the resultis that the part of the picture you actually want - e.g. the personor the building in the foreground - will be underexposed..

A simple remedy for this is to point the camera down so that there isno sky in the viewfinder and take a meter reading off the groundwhich will be about right. Hold down the exposure-lock button (orhalf-press the shutter to lock exposure and focus). then re-framethe shot and take the picture; the exposure will now be (more)correct for the foreground subject..

This is about the simplest example of what can be difficult inunusual lighting conditions, but I hope it illustrates the point..

+ followup question: if you hold down halfway the shutter button it locks the focus AND the exposure? I thought the AEL locks the exposure?i'm confused with the center and spot metering whats really the difference?..

Comment #6

Sorry, Earl, I'm not following. If I recompose as I said earlier, doesn't the camera just do what I told it to do? Are you saying that despite my shutter, aperture and ISO settings being set while pointed elsewhere, the camera's meter will shorten (or in any way change) the exposure settings when I reframe? I apologize for my ignorance...

Comment #7

Teris wrote:.

Sorry, Earl, I'm not following. If I recompose as I said earlier,doesn't the camera just do what I told it to do? Are you saying thatdespite my shutter, aperture and ISO settings being set while pointedelsewhere, the camera's meter will shorten (or in any way change) theexposure settings when I reframe? I apologize for my ignorance..

Don't worry, you will get it soon. Just keep reading exposure and metering threads..

Yes, if you recompose after aiming the camera downwards to prevent the bright sky from affecting the meter, (and lock exposure) then after recomposing, it will do just what you told it to. In other words, after you meter on a more average type reflectance, and lock the exposure, then when the meter sees the bright sky it will not change your pre-selected exposure..

P.S. you can't be ignorant, or you wouldn't be asking intelligent questions...

Comment #8

+ followup question: if you hold down halfway the shutter button itlocks the focus AND the exposure? I thought the AEL locks theexposure?.

This is an option which can be preset on my camera (combining AE and focus lock). It was probably not a good example to use as it is one step more complicated than the question you were asking, so forget about it for the moment..

If your camera has an AE lock button, just hold that down whilst pointing the camera at an averagely-lit part of the scene (e.g. the ground), then recompose the picture and shoot. The camera may tell you that the exposure is now incorrect but it's stupid so ignore it..

I'm confused with the center and spot metering whats really thedifference?.

Spot metering, as it's name suggests, just takes a reading from a small spot at the centre of the frame (often the area covered by the central autofocus point). This can allow you, for example, to take a meter reading off somebody's face whilst completely ignoring the bright sky in the background - so you would get a good exposure without having to use the AE lock and recomposing..

However the spot is so small that you may get a non-representative part of the picture... if something dark (e.g. dark hair) is in that spot, the camera will be fooled into giving a long exposure and the picture will end up overexposed. If a bright part of the picture is in the centre spot (e.g. a white shirt, teeth when someone is smiling) then conversely the camera will be fooled into giving a too-short exposure and the shot will be underexposed. So spot metering can be very helpful but needs using carefully..

Center metering (center weighted) takes a meter reading from most of the frame but biased towards the centre, which makes sense because that is where the subject usually is. I use this as the default setting..

The common metering modes are explained succinctly here:.

Http://en.wikipedia.org/wiki/Metering_mode.

Best wishesMike..

Comment #9

Thanks, Earl. I think I wasn't following most of this because I use Manual setting. I guess AE lock has no functionality in Manual...

Comment #10

Teris wrote:.

Thanks, Earl. I think I wasn't following most of this because I useManual setting. I guess AE lock has no functionality in Manual..

That's right. In Manual mode the camera does not control the exposure at all, it is entirely up to you. Once you set the shutter and aperture it doesn't matter how you recompose or where you aim the camera, it just sticks with the settings you have given it..

Also, it's worth noting that the camera will retain those settings even after you turn it off. So if for example you have been shooting in low light with extreme shutter and aperture settings, the camera will retain those settings next time you turn it on, even in bright conditions..

It is my habit to turn the camera to Auto, or Program, before turning it off, just in case I want to take a quick "grab" shot next time I turn it on (rather than being stuck with whatever the last manual settings were)..

Image control:Zoom outZoom 100%Zoom inExpand AllOpen in new window..

Comment #11

Thanks - that's what I thought. I just couldn't understand what the big deal was about AE lock!..

Comment #12

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This question was taken from a support group/message board and re-posted here so others can learn from it.

 

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