Archived posting to the Leica Users Group, 1999/07/27
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]>omegaman wrote: >> >> Alex Brattell wrote: >><snip> >> > What does the 'f' in f-stop stand for? >><snip> >> Alex: >> The "f" in f-stop stands for focal length. If you have a 50mm lens and >> have it set at f/8, then the product of 50/8 (50 divided by 8) is the >> size of the opening made by the iris. In this example the lens opening >> at f/8 is 6.25mm. 100mm at f/16 has also a 6.25mm opening. >> Randolph Carlisle > >It's lucky people especially beginners don't know that. I wouldn't bandy that >info around. >So you are closing or opening the little aperture thing and what does F stand >for? Length! >Pretty metaphysical! No wonder that is on a need to know basis! > >But it's really on the same level as talking about the "speed" of a lens. >Another curveball. >It's like a bunch of photographers got together and came up with doubletalk >terminology designed to keep people out. >"Oh no I'm not just clicking this thing I've got all this metaphysical mumbo >jumbo going on." >Mark Rabiner The reason the expression is f/a number is that it is based on a mathematical expression, ie, f - the focal length divided by the true physical entry pupil diameter gives you the 'aperture', which actually means aperture ratio. Somebody just screwed up in the late 19th century, confused some of the components and gave us a mangled expression. I still find it easier to deal with than the logarithmic EV sequence. I mean, does a minus EV value mean that the film has to illuminate the scene through your Noctilux in order to reach as least a neutral 'Exposure Value'? My cameras have only so much Phlogiston to give to the dark scenes out there. * Henning J. Wulff /|\ Wulff Photography & Design /###\ mailto:henningw@archiphoto.com |[ ]| http://www.archiphoto.com