F-number. Diagram of decreasing apertures, that is, increasing f-numbers, in one-stop increments; each aperture has half the light gathering area of the previous one. In optics, the f-number (sometimes called focal ratio, f-ratio, f-stop, or relative aperture[1]) of an optical system is the ratio of the lens's focal length to the diameter of the entrance pupil.[2] It is a dimensionless number that is a quantitative measure of lens speed, and an important concept in photography.
Notation[edit] The f-number N is given by where is the focal length, and is the diameter of the entrance pupil (effective aperture). A 100 mm focal length f/4 lens has an entrance pupil diameter of 25 mm. A T-stop is an f-number adjusted to account for light transmission efficiency. Stops, f-stop conventions, and exposure[edit] A Canon 7 mounted with a 50 mm lens capable of an exceptional f/0.95 A 35 mm lens set to f/11, as indicated by the white dot above the f-stop scale on the aperture ring.
F/1 = , f/1.4 = , f/2 = , f/2.8 = (i.e., Zarias.com :: The blog of editorial photographer Zack Arias. Loft 19 Studios - Phoenix, Arizona. Prerequisite skills: -Basic camera operation -Basic lights/grip operation -Metering Light -Key & Fill Light Placement -Color temperature Creating a pure white background can be one of the most difficult and frustrating exercises for a beginning photographer.
Many theories and "formulas" exist for achieving pure white, but in reality, achieving pure white is more importantly a matter of managing and avoiding the negative side effects that can accompany a high-key lighting situation. Making the background white is the easy part of the setup. In a portrait situation, this can be accomplished by overpowering a white wall or roll of seamless paper behind your subject with light, opening up the aperture on your camera until the background is over-exposed, or a combination of both.
However, as many of you have no doubt encountered, your images do not turn out the way that you expect. This is our setup in its simplest form, with no lights added as of yet. 1. There you have it. Good luck, Studio Information Reference. Photography Jobs : What Is an F-Stop?