Archived posting to the Leica Users Group, 2003/07/21
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]On Monday, July 21, 2003, at 03:31 PM, George Lottermoser wrote: > Quite true. It is the close focusing wide open which has recently been > disappointing me. Never a problem in the past. For a while I thought > it was my old eyes playing tricks. So I set the ruler down at > 45degrees and bolted the bodies to the studio stand and was shocked > when I looked at the negs. At closest focus on the M6 classic the 75 > and 50 luxes focused an inch behind the intention point. At closest > focus on the M6 .58 TTL they focused an inch in front of the intention > point. Likewise on the .58TTl the 35 lux asph focused almost an inch > and a half in front of the the intention point and almost spot on with > the M6 classic. So these first tests would indicate that everythings > drifted off quite a bit all three lenses and two bodies - unreliable > wide open - I’m sending the 28 along just to get it all back to > factory specs. That’s the bad news. The good news, I quess, would be > that these things are adjustable and able to be brought back to > precision. > > I have a feeling that these levels of precision will disappear in our > new digital world. Maybe I’m wrong. When folks talk about missing > focus in the AF cameras - where is the miss taking place? In the > electronics? In the intention? In the precision of the electronic and > mechanical interface? Where and how would one adjust? Well, since AF works on finding the maximum local contrast in an image, the only thing that can be going wrong is that you or the system are focussing on the wrong thing. The problem with rangefinders is that you aren't focussing the image, per se, your are manipulating a mechanical linkage and you trust the mechanism to put the lens in focus when the rf images co-incide. In an AF system you are not manipulating B in the hope of getting A right, you are directly looking at A and adjusting it. Just as in an SLR. AF is of course not remotely infallible and can be confused by low light, rapidly moving objects, lack of texture, reflections, scratches in glass... at which point you flick the little switch on the lens from AF to MF and carry on. I would say that - - For well lit subjects on medium lenses, AF is marginally faster than RF and as accurate. - - For poorly lit or low contrast subjects on medium lenses, the RF wins for me. - - For poorly lit subjects at close distance, the AF is generally more accurate unless you have really calibrated your RF as described above. - - For lenses 75mm and greater, especially wide open or in poor light, AF is better than RF but MF on an SLR is better than both of them. Those are my personal prejudices. The probably don't reflect anyone else's experience. - -- John Brownlow http://www.pinkheadedbug.com http://www.unintended-consequences.com - -- To unsubscribe, see http://mejac.palo-alto.ca.us/leica-users/unsub.html