Archived posting to the Leica Users Group, 2002/05/29
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Thanks, Henning. I found that formula. My calculations are related to infinity focus, so M=0. If you start closing in, you need to take into account the extension (via lens focal length) for effective f/stop and the calculations become more messy. Regards - ------------ Dante Stella On Wed, 29 May 2002, Henning Wulff wrote: > > > > >> 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 > - -- To unsubscribe, see http://mejac.palo-alto.ca.us/leica-users/unsub.html