What does stopping down mean in photography?

Answer 1

The following applies to an SLR and may not apply to a DSLR.

It can mean either:

a) simply reducing the light transmitted to the film or camera sensor by way of adjusting the aperture so that it is smaller.

b) manually reducing the aperture from full-open before taking the picture to either

i) preview the depth of field through the viewfinder or

ii) take a meter reading at the aperture that will be used for the shot in order to arrive at the corresponding shutter speed or

iii) take the shot with the aperture stopped down, forcing the camera meter to calculate the shutter speed at the moment of exposure. The latter two are referred to as stop-down metering. To do so and allow ambient light to enter the viewfinder eyepiece (say, because you mount the camera on a tripod and stand back from the camera) would be a mistake since light entering the eyepiece will alter the meter reading.

One reason for performing stop-down metering is because the lens has been attached to the camera body by means of a reversing ring. In this case, the lens levers and pins cannot transmit the aperture information to the camera in order for the meter to calculate the exposure. Not all cameras have stopped-down metering capability, for sure. My old Canon A1 does, and has a lever controlled metal blind that covers the eyepiece to prevent stray light from entering.