Originally posted 2013-04-12 19:28:25.

In the last article we looked at the optical principles that govern focus and depth of field. Now let’s explore how these are applied practically in the camera. For the moment we will assume that we are using a single-lens-reflex (slr) or rangefinder type camera, either digital or film.
If you look at the lens barrel you will probably see a ring which controls the aperture diaphragm. This will be numbered in f-stops, which on modern cameras will run f1.4,2, 2.8, 4, 5.6, 8, 11, 16, 22, (32, 45, 64). I put the last three in brackets because you’re pretty unlikely to have them but you might see them on view cameras. Note that the numbers double on every second step—2,4,8 etc and 2.8, 5.6, 11 etc. The f-stops are determined by dividing the effective aperture into the focal length, so a 50mm lens with an aperture of 25mm is f2, and with 12.5mm is f4. Each f-stop, going from low number to high, admits half as much light as the one before, so f2.8 is half of f2 etc. It’s easy to work out why if you’re mathematically inclined, but if not, just remember it.
Continue reading “Stopping down, Depth of Field and Bokeh”







