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I've read in the manual that using the exposure lock (EL) button in conjunction with matrix metering can give unpredicable results. Can someone explain why this is so?

I usually use the EL button in lock-and-hold mode when shooting multi images for panoramas to hold the exposure for the series of images, and since reading this had reverted to center-weighted metering. If you meter the correct exposure for on image, how can locking the values give unpredicatable results?

Alistair

Matrix metering divides the view up into segments and meters each one. Based on where the light/dark segments are found it makes a guess at the kind of picture you are taking and tries to expose correctly for that situation. If you lock the exposure and then change the composition the locked exposure doesn't represent your new composition.

Instead of using exposure lock I switch to Manual mode & use spot metering to get it right.

On page 75 for those playing along at home...

Read in conjunction with the reference in pg 84, it seems to me the manual writers are specifying that when one would normally use exposure lock it is more suited to be used in conjunction with CAW or spot metering.

It didn't state that matrix will give unpredictable results, it stated 'undesireable'. This would be true, given what we know about matrix metering - ie. it reads the luminosities (and colour and lens focus distance info in certain cases) from the 1005 segments of the frame (in the case of the D70) and compares this to what the firmware's has programmed to determine the type of scene you're likely shooting, and calculates the exposure to optimise it.

We can never predict which area(s) the matrix meter chooses to render as middle grey. With CAW or spot, it's more straightforward - the centre of the frame is given greater weight, or the reticle corresponding to the chosen AF point. In both cases the exposure meter tries to render what it sees as middle grey.

If utilising the autoexposure lock function, it is presumed that you know what you want as the metered reading, and want to preserve those exposure settings (ie. combination of ISO, aperture and shutter speed) within the multiple frames you intend on shooting - eg. for a panorama. It wouldn't make sense thus to use matrix metering exposing for the entire scene when you can't tell which part of that scene (if any) the camera's exposure meter is rendering as middle grey.

Resist the ad-hominem attacks, read up on what Ken has to say regarding the most advance exposure meter available.