Date: Wed, 06 Jun 2001 21:09:52 -0600 X-Mailer-Version: 20010509 X-Recipient: azn@nemeng.com From: John Collier Subject: Re: [Leica] Rangefinder calibration Message-ID: References: Two sequential messages from the archives on rangefinder adjustment: - ---------- From: Rick Dykstra Reply-To: leica-users@mejac.palo-alto.ca.us Date: Mon, 15 May 2000 10:55:37 +1000 X-Mailer-Version: 20010509 X-Recipient: azn@nemeng.com To: leica-users Subject: [Leica] rangefinder adjustment - long Hi folks. On the topic of rangefinder adjustment ..... It's one thing to calibrate the lens to the rangefinder, but it would be nice to know that the subject is then focussed on the film plane. To check that, a focussing screen resting on the film guides is needed. More on this later. When I look through the lens mount of an upside down M6, I see three slotted screws. The following describes what I think they're for. The screw closest to the lens mount supports a roller that rides on the lens' cam as the lens is focussed. This screw appears to be eccentrically mounted on the rangefinder arm. Turning this screw would adjust the relationship between the lens' cam and the rangefinder. This looks like the screw for fine adjustments to the way the rangefinder reads the lens' cam. The second screw in from the lens mount holds the rangefinder arm onto a swivelling pin that descends from the optical unit. Between this screw's head and the rangefinder arm is an eccentric washer, that itself sits within a recess of the rangefinder arm. I see two possibilities here. If this second screw was partially tightened, then the eccentric washer, upon being rotated clockwise, would serve to hold the arm in the right place before the screw is fully tightened. On the other hand, if the rangefinder arm has a slotted hole, then the eccentric washer could be rotated to lengthen or shorten the extension of the rangefinder arm from its pivoting point. I think the former of the two possibilities is the correct one. This second screw and the eccentric washer look like they're for rough setup adjustment of the rangefinder, with the eccentric roller screw (the first screw) being for fine adjustment. The third screw in from the lens mount is also surrounded by an eccentric washer. Lying against the washer is a metal arm with a twist in, held by and pivoting from the second screw. This arm comes into contact with the third screw's eccentric washer when the rangefinder arm moves all the way forward, such as when the lens is removed. Loosening the screw and turning the washer would adjust the forward most limit of the rangefinder arm's movement, and might protect other elements within the rangefinder system from being knocked around when the lens is removed. *** So, if an M6 rangefinder does not show correct focus when the lens is focussed at the film plane, to my way of looking at those screws, its the first screw, the one with the roller, that should be adjusted. I'd leave the other two alone. A while back someone on list pulled from the archives a description of how to bend a pair of slotted screwdrivers for this adjustment job. One ends up with the screwdriver tip in line with the right angle bend and the other with its tip square on. Someone else recently mentioned that the arm should be supported when the roller screw is being adjusted. The adjustment itself - trial and error! In making an adjustment, one could either set the lens to infinity and adjust the rangefinder to suit, accessing from the back with the lens attached if feeling confident. Or, focus the lens on an object up close by viewing a focussing screen sitting against the film guides and then take the screen away, stick the screwdriver in from the back and adjust the rangefinder to suit. Leica workshops have a jig, a lens and I think a focussing screen for doing the latter. With the adjustment done for up close focussing, intermediate and infinity focussing is then assessed. If the rangefinder is out at infinity, then it would appear to be the lens that's at fault. Uh oh. How does all that sound? I'll stand by while you get to work with your screwdrivers. On your cameras! Or, send 'em to me and I'll have a go. So far, mine haven't needed adjusting, but you can see I'm looking forward to the day that they do! Rick Dykstra - ---------- From: John Collier Date: Mon, 15 May 2000 00:17:07 -0600 X-Mailer-Version: 20010509 X-Recipient: azn@nemeng.com To: Subject: Re: [Leica] rangefinder adjustment - long - longer! The three screws are almost exactly as you described. The third screw with the eccentric behind the rangefinder's arm limits the "inward" travel of the rangefinder arm and the thin "flap" off the rangefinder pivot that contacts this same third adjustment limits the "outward" travel. So we can limit the rangefinder's movement, not something that we need lose sleep over, and we can also adjust the roller's vertical position by bending the arm. These adjustments are factory set and only need readjusting after catastrophic events such as we have nightmares about. Let us disregard them. The roller is indeed on a eccentric screw and it does the fine adjustment of the rangefinder's arm rotational position. The rangefinder arm is attached to the rangefinder mechanism at the pivot end by yet another eccentric. This one has a lock screw and the eccentric is adjusted by moving the slotted tab. This adjusts the range of rotation a given lens cam movement will impart by changing the length of the arm. A shorter arm gives more rotation and a longer arm gives less rotation. One checks the rangefinder at infinity, at 10 meters and at 1 meter. One has to adjust the length of the arm so that when the roller eccentric adjustment is done to give correct indication at infinity, the other two are correct as well. It is a Zen thing. The factory and distributors do not use lenses to do this but a special jig with a mount for the camera and a target with all the various marks so you can do the above adjustments and more. The rangefinder arm is worked with a special tool that mounts on the lens bayonets and has stops for each of the three measuring points. Cool. The more I learn about this the more inclined I am to leave it alone ;-). One could easily rig up targets at fixed distances but one would have to use a ground glass to compare focus between the rangefinder and the film plane. I hope this has helped to clear things up somewhat. After a good solid whack, it is not unusual for the infinity indication to be off. Commonly people then reset the roller position to correct things. I do not know what actually gets shifted but it is reasonable to assume that range of rotational movement does not need to be changed, so we do not have to adjust the length of the arm, but that the infinity just needs to be reset by adjusting the roller. A very long winded reply to say: Yes, tweak the roller eccentric for minor in service adjustments. John Collier