Stopping down is a reference to the aperture f-stop of your camera lens, and denotes changing it to a smaller size. F-stops on a traditional 50 mm lens usually run from F2 thru F32, F2 being the largest opening allowing the maximum amount of light in, while F32 is the smallest opening, allowing the smallest amount of light in. Stopping down comes with a duo of benefits. When you discover yourself in an extremely bright environment, stopping down will provide you with a greater tone range (less contrast) while enhancing the depth of field.
Darker images at the film plane is also the result. Photographers can counterbalance for this by upping the
exposure time, raising the
ISO setting, (in digital cameras, boosting sensitivity of light to the image sensor.)
A somewhat inaccurate assumption exists that by stopping down photo sharpness is increased. This holds true for out-of-focus subjects, and cameras with cheap or poorly built lenses, due to coma,
spherical aberration, and
astigmatism) not being as readily noticeable at smaller apertures. Better quality lenses have been corrected for aberrations, and usually provide the sharpest images of in-focus subjects around one to two f-stops below the full aperture setting. On very narrow apertures, diffraction decreases sharpness. The sharpest image is generally obtained by stopping down by one to two
f-stops as lens engineers optimize their lens designs for a concession between letting in the maximum light to cut down on exposure time and creating a sharply focused image. Now if the lens engineer only optimized for sharpness, the lens would possess a small minimum aperture while being it's sharpest at maximum aperture, but would create an image too dim for some poor light environments.
Jan 11, 2010 -