You can tell the meter is on when the green digits below the viewfinder image light up (there's a menu option that
controls how long the meter stays on - use if if the digits shut off too quickly for your taste). Because it's a manual
lens, the camera has no idea what f/number you've set it to, so it will show "F(blank)" for the aperture.
And here's the secret to metering with the manual lenses: while the meter is still on, press the "AE- L" button on the
back of the camera (it'll probably be very close to where you thumb naturally sits):
When you hit the button the camera will momentarily stop down the lens to take a light reading, then it will set the
shutter speed to the appropriate exposure. You'll see the new shutter speed in the green digits below the
viewfinder image. After setting the shutter speed the lens will immediately open back up again - the whole thing
takes about a second.
If you think the shutter speed is to slow (or too fast!), adjust the aperture (or ISO sensitivity) and repeat (half- press
the shutter to turn on the meter and then press the AE- L button to set the shutter speed).
Everything is set, now just fully depress the shutter button to take the picture:
