Archived posting to the Leica Users Group, 1999/07/27
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]- --------------849EC4A3833A5505B204537A Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Alex Brattell wrote: > > > > What does the 'f' in f-stop stand for? > (I've asked people and looked in books, and had to admit to the person who > asked me - haven't got a clue!) > > thanks > alex > > Alex, The correct term is really f-number. The "f "comes from focal length. and the f-number is the result of the focal length divided by the diameter of the entrance pupil of the lens. So, if the focal length is say 100mm, and the front element of your lens is 25mm, then the f-number is 4. The term f-stop, should only be used, if your lens has an adjustable diaphragm to stop down the amount of light which is transmitted through the lens. Regards, Horst Schmidt > _ - --------------849EC4A3833A5505B204537A Content-Type: text/html; charset=us-ascii Content-Transfer-Encoding: 7bit <HTML> <P>Alex Brattell wrote: <BLOCKQUOTE TYPE=CITE> <BR> <P>What does the 'f' in f-stop stand for? <BR>(I've asked people and looked in books, and had to admit to the person who <BR>asked me - haven't got a clue!) <P>thanks <BR>alex <P>Alex,</BLOCKQUOTE> The correct term is really<B><I> f-number</I></B>. The <B>"f "</B>comes from <B><I>focal length</I></B>. and the f-number is the result of the focal length divided by the diameter of the entrance pupil of the lens. <P>So, if the focal length is say 100mm, and the front element of your lens is 25mm, then the f-number is 4. The term <B><I>f-stop</I></B>, should only be used, if your lens has an adjustable diaphragm to<B><I> stop down</I></B> the amount of light which is transmitted through the lens. <P>Regards, Horst Schmidt <BR> <BLOCKQUOTE TYPE=CITE>_</BLOCKQUOTE> </HTML> - --------------849EC4A3833A5505B204537A--