Archived posting to the Leica Users Group, 2001/02/06
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]I do not want to go too far in explaining things as I quickly get out of my depth in this field :-). The critical adjustment with the M rangefinder and the 75mm lens wide open, is not the infinity adjustment but the length of the rangefinder arm. If you take off the lens and look at the rangefinder arm, the one with the roller on the end, the length of the arm is adjusted at the arm's pivot point. There is an eccentric cam that varies the effective length of the rangefinder arm. The infinity adjustment is the eccentric mounting screw for the roller. The length of the arm controls the rate at which the rangefinder mechanism rotates in relationship to the movement of the roller against the lens cam. A short arm gives a greater rate of rotation as compared to a longer arm (get a straw, spoon, etc and try it). As we are aiming for a 6mm to 8mm window when the lens is close focused, the arm has to be calibrated very carefully. The lens cam can be off slightly as well. You do not adjust the pitch of the cam thread :-), that is matched up at the factory, but just its starting point. Again, it is not that fussy at infinity compared to how close it has to be when the lens is focused close. If you have a rangefinder tolerance of +/- x and a lens tolerance of +/- y. It is easy to see where a camera with a rangefinder set at +x tolerance will have troubles hitting that 6mm to 8mm window with a lens that has a near focus tolerance of -y. If your primary lens is a 50/2.8 or a 35/2.8 you will never even notice if your rangefinder is off enough to drive you crazy with a 75/1.4. John Collier > From: "Steve LeHuray" <icommag@toad.net> > >> Wide open and focused close, the depth of field of the 75/1.4 is between 6mm >> to 8mm (just over a quarter inch). This is remarkably difficult to calibrate >> for and, what amazes me, is that it can be done. Gerry at Kindermann Canada >> sometimes has to have the whole kit so that everything can be calibrated >> correctly. >> >> John Collier > > John, > > So does that mean once calibrated you should essentially weld that 75/1.4 to > the body? And would this also apply to the 50/1.0 and 1.4? > > Steve > Annapolis > >> >>> From: Andrew Moore <dmm@bronze.lcs.mit.edu> >>> Subject: [Leica] how can the 75 Lux focus go bad? >>>>> >>> I keep hearing people's accounts of their 75 Summiluxes focusing in front >>> of or behind the intended point of focus (recently 4 people and 5 lens >>> samples). In a couple cases the lens (alone) was sent out for repair and >>> came back working. >>> >>> When these lenses go out of spec, what exactly is happening to them? >>> >>> --Andrew >>> NO ARCHIVE >>> >>> >> >