Archived posting to the Leica Users Group, 2003/02/14
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Henning Why don't the doubters realize, that with a short focal length lens, any error in the back focus becomes a greater proportion of it's movement from infinity to (say) 1 meter. Jerry Henning Wulff wrote: > At 9:30 AM -0800 2/14/03, Jacques Bilinski & Barbara Bradbury wrote: > > > I'm sure this has been covered but why would you test a lenses/bodys focus > >> using a wide angle @ infinity? Wouldn't you want to use a tele @ the > >minimum > >> focusing distance ??????????????????????????????????????????? > >> > > > >You want to do the test at infinity rather than a close focus distance in > >order to test the lens/body compatibility independantly of the rangefinder > >adjustments. Rangefinders in RF cameras easily get out of adjustment if the > >camera is banged, and this won't play a part in the test if you do it at > >infinity. > > > >You want the widest aperature lens you have in order to minimise the depth > >of focus (i.e. depth of field inside the camera at the film plane). > > > >Focal length doesn't matter, contarary to what is often written on this > >list. Best lens for this test is a Noctlux. > > Focal length can make the test easier because if the flange - film > distance is 1mm too large, the lens will be focussed at a shorter > distance; with a wide angle lens this distance will be significantly > closer to the camera than with a longer focal length lens, and thus > the discrepancy will show up. As I mentioned before, if the > discrepancy between the Hexar and the Leica bodies is as large as > some have said, a 35 lens would focus at about 6m instead of > infinity. A Summilux wide open would show this discrepancy easily. A > Noctilux would focus at about 12m with the same film - flange > discrepancy; that is why it is easier to see with a wideangle lens. > > -- > * 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