Light meter at “zero” means a good picture. Right?

Wrong.

Shoot something black, filling the entire viewfinder with that object, and make sure the light meter points at “zero” as you are pointing at the subject (use the viewfinder!). Take the picture.

You get this:

The histogram shows why this is bad:

A histogram of a black object should peak on the left (the dark side).

Now do it again, with the light meter pointing at –2 (minus 2):

Perfect. Look, the histogram is right for this type of scene:

The moral of this post:

• “The meter displays zero” does not equal “this will be a good picture”. It merely means “this will be a mid-grey picture, neither dark nor light”.
• “The meter points to minus” does not equal “this will be a bad picture”. It merely means “this will be a dark picture”.
• “The meter points to minus” does not equal “this will be a bad picture”. It merely means “this will be a dark picture”.

And there you have it. Now you understand the camera’s built-in light meter.