Archived posting to the Leica Users Group, 2002/05/29
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]> > >> Can someone point me to a formula for calculating depth of focus for a >> given focal length and aperture? This is NOT depth of field, but rather >> the focus zone on and around the film plane. >> >> Thanks >> ------------ >> Dante Stella >> >> > >Dante, > >I think there is a formula for that in Jonathan Eastland's 'The Leica M >Compendium' > >sl If you are using the lens at low magnifications (ie, not macro) then the depth of focus (t) is t=2CN where C is the circle of confusion and N is the f-number. Depth of focus is independent of lens focal length, and is only aperture dependent. In general, t=2CN/(1+m), where m is the magnification. This is due to the fact that to focus closer, the lens has to be moved away from the film plane, causing the cone of light to narrow, which is the same as stopping a lens down. So actually the first formula is always correct, as long as you use the effective f-number, taking into account lens extension. - -- * Henning J. Wulff /|\ Wulff Photography & Design /###\ mailto:henningw@archiphoto.com |[ ]| http://www.archiphoto.com - -- To unsubscribe, see http://mejac.palo-alto.ca.us/leica-users/unsub.html