Archived posting to the Leica Users Group, 2003/01/14
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Rei, I think you should be doing this from the film prospective, as the "o" does not move...but the L turns. The distance from "o" to "L" does not change, but since the film is planar with L, there is a slight deflection... He is claiming 5.3cm, which is more than 2 inches. The film is only 1.5" wide, and therefore the maximum movement that could occur at 90 degrees is .75". So, a small angular movement of 10 degrees will hardly make for a 2" displacement in the film position. Austin > -----Original Message----- > From: owner-leica-users@mejac.palo-alto.ca.us > [mailto:owner-leica-users@mejac.palo-alto.ca.us]On Behalf Of Rei > Shinozuka > Sent: Tuesday, January 14, 2003 1:52 PM > To: leica-users@mejac.palo-alto.ca.us > Subject: Re: [Leica] Useful link for focus adjustment > > > let me try. > > i think this is the idea. object "O" in center of plane of focus for > lens "L", distance OL is 100cm. > > -------O------- > \ | / > \ | / > \ | / > L > > > now rotate L counterclockwise (or O clockwise around L) > distance OL is still 100cm. now create a plane intersecting > point O perpendicular to the lens axis, and define point X as the > intersection of that plane and the lens axis. distance XL is > less than OL. if view angle of lens were 90 degrees, than the > distance XL would be about 71 cm (100/sqrt(2)). > > if we assume that lens L renders a sharp plane of focus > perpendicular to its axis, then X and O are on the same > plane of focus. therefore to get O at the edge of the frame > in focus, you need to set focus to 71 cm, despite the fact > that the object is 100cm away from the lens. > > --------------- > --\-----X----O-- > \ | / > \ | / > L > > forgive the sloppiness, i have not done trig or geometry > in the latter half of my life, and i was never a particularly > able practitioner. :-) > > -rei > > > On Tue, Jan 14, 2003 at 10:14:30AM -0800, Herb Kanner wrote: > > > > I absolutely don't understand Martin Tai's geometry. He claims that > > if the subjects eye is 100 cm from the camera as indicated by the > > scale on the lens barrel and is in the center of the image, that if > > the camera is rotated so that the eye is now at the edge of the > > frame, it's distance will have been reduced to 94.7 cm. This looks > > like utter nonsense. Can anyone prove it to be correct? > > > > Herb > > > > ------------------------------------------- > > Original Message: > > > > For those who haven't seen it, I can recommend Martin Tai's Leica M & Rs > > recompose focus guide. Great for understanding how to be able to compose > > shots that are not head on while maintaining precise focus even at full > > aparture, this was a bit hit and miss for me before even with SLRs > > (although easier). > > > > http://www.accessv.com/~martntai/public_html/Leicafile/recompose.html > > -- > Rei Shinozuka shino@panix.com > Ridgewood, New Jersey > > -- > 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