luigi bertolotti Posted February 20, 2007 Share #21 Posted February 20, 2007 Advertisement (gone after registration) I've never seen it in print either, Luigi, but I worked for Leica when the CL appeared and these are the numbers I was given. It's a simple matter: Since the M lenses have a flat cam, arranging the cam-tracking roller to be in the center of the lens opening wasn't part of the camera specification. Most of the time, the focus-tracking roller is centered, but not always. Since the CL lenses have a sloped cam, the focus-tracking roller on all CL bodies is centered; that way the CL cam tracker will meet the focus cam at the point for which it is adjusted. The problem arises when you mount a CL lens with sloping cam on an M body whose rangefinder cam tracking roller is off center. The M body works fine with flat-cam lenses and meets specification; and the C lens works as it's designed to do with the CL. But the off-center cam roller in the body now meets a sloping cam in the lens and focus is off. (This isn't a rangefinder adjustment issue since the M body specifications never required a centered focus tracking cam roller.) Two of my three M bodies have off-center focus trackers. Other people (e.g. CameraQuest) seem not to have run across the phenomenon. I don't know what the actual percentage of M bodies produced with off-center focus cam rollers is, but I was told at the time that it was "about 25%." I think the same figure was still cited at least at the time of the M6, but perhaps at some later time, Leica decided to start requiring that the cam tracker be centered in the M bodies. If we can find one M8 with non-centered focus cam tracker, we will know that the old design standards still hold even with the radically changed rangefinder. Thanks for asking. I hope I haven't made it seem complex. It is literally a matter that you can recognize at a glance once you understand what's involved. --HC THANKS A LOT, HOWARD ! You really have clarified to me the matter : I had never imagined, without your explanation, that the exact positioning of the cam tracker was not a specification of M bodies assemblies. I perfectly understand the issue: for my pleasure, I tried to make a 3D CAD model of the VF/RF assembly of M4...oh, I would like a lot to have the original dimensioned drawings...I had to invent a number of dimensions... Link to post Share on other sites More sharing options...
Advertisement Posted February 20, 2007 Posted February 20, 2007 Hi luigi bertolotti, Take a look here 40mm M.Rokkor on M8. I'm sure you'll find what you were looking for!
ho_co Posted February 22, 2007 Share #22 Posted February 22, 2007 THANKS A LOT, HOWARD !You really have clarified to me the matter : I had never imagined, without your explanation, that the exact positioning of the cam tracker was not a specification of M bodies assemblies. Exactly. I imagine that's one reason it was never put into print. M bodies were bench-built, to a great degree by feel, even to the location of the cam tracker. I perfectly understand the issue: for my pleasure, I tried to make a 3D CAD model of the VF/RF assembly of M4...oh, I would like a lot to have the original dimensioned drawings...I had to invent a number of dimensions... Luigi-- Can't help you there. It's a beautiful thing to hold in one's hand, isn't it? But in fact, this enters into an even stranger area: Wetzlar was of course ready to end M production when the M5 did not sell, but Leica Canada told them, "Hey, send us the dies and drawings for the M4 and we'll put it back into production." That much is well known. But from what I understand, Wetzlar didn't send Midland a lot of details because they didn't have them. The workers simply knew what hardness grade metal had to be used, or what the trick was to assemble two parts, even what the dimensions were of those parts. The Midland workers had to re-invent them. That's why the earliest Canada attempts at reintroducing the M4 didn't feel quite the same as the German product. So I can feel for you in trying to figure out what the dimensions and tolerances must be! Even Germany couldn't have *told* you what the numbers were in many cases, but would have been able to *show* you. It's one of those strange miracles that have made Leica unique! --HC. Link to post Share on other sites More sharing options...
ho_co Posted February 22, 2007 Share #23 Posted February 22, 2007 Would you mind to explain what you mean by "off-center" cam roller? LCT-- Sorry; in trying to make things explicit I sometimes make things seem overly complex. Look at the camera from the front. Remove the lens. Now you see the bayonet and the shutter cavity. Imagine a line perpendicular to the top plate bisecting the circular lens mount. In most but not all cases, the center of an M body's cam tracking roller will fall on that vertical bisector. About 25% of the time (from what I'm told), the cam tracker will not fall on that center line. That's what I mean by "off-center." --HC Link to post Share on other sites More sharing options...
roberth Posted February 22, 2007 Author Share #24 Posted February 22, 2007 If you don't want to get into filing your lens, one trick is to not quite fully click the bayonet mount into position. This will also display the 35mm framelines. It also indicates just how little grinding is required on the lug to modify the lens. Rex considering how tight my lenses are on the M8 not having them fully clicked in is feasable. I'll give it a shot. Link to post Share on other sites More sharing options...
lct Posted February 22, 2007 Share #25 Posted February 22, 2007 ...In most but not all cases, the center of an M body's cam tracking roller will fall on that vertical bisector.About 25% of the time (from what I'm told), the cam tracker will not fall on that center line... Thank you Howard but i don't understand why this would have a different effect with flat-cam or sloping-cam lenses. The cam tracker moves up and down when focussing so my feeling was that the only diffence between M and CL lenses is this move is faster with the latters due to their sloping cam. Am i missing something? Link to post Share on other sites More sharing options...
ho_co Posted February 23, 2007 Share #26 Posted February 23, 2007 LCT-- On a sloping cam, the center part of the cam is aligned to give accurate focus. Move the tracker a couple milimeters one way or the other and you're reading a different part of the cam and therefore a different focus. On a flat cam, the whole of the cam relays the same focus information; moving the tracker a few milimeters either way will make no difference. I think you're confusing this with the pitch of the focusing helicoid, which determines how the rotational movement of the focusing mount is translated into the forward-back movement of the lens within its mount. The flat or sloping focusing cam is the cam that passes the focus distance from the lens to the cam tracker part of the rangefinder. As I recall, one way the CL lenses were kept so small was to combine the focusing mount of the lens with the focusing cam itself. That made it necessary to use a sloped cam, but that may also be the source of the confusion here. DEMONSTRATION: If you have a CL lens (sloped cam), try this: Put it on the body, focus to infinity, look through the rangefinder to verify that you are at infinity. Now leave the lens set to infinity but unlatch it and rotate it, say, 5 mm, as if you were removing it from the body. Now check the focus distance the rangefinder shows; since the focus cam is in a different place relative to the cam tracker, and since the cam itself slopes, the indicated distance will have changed. Do the same with a flat-cam lens and there will be no indicated change of focus. Hope this helps. --HC Link to post Share on other sites More sharing options...
lct Posted February 23, 2007 Share #27 Posted February 23, 2007 Advertisement (gone after registration) ...On a sloping cam, the center part of the cam is aligned to give accurate focus.... Looks like it's less and less clear to me, sorry Howard. Isn't this the sloping cam here? Link to post Share on other sites More sharing options...
ho_co Posted February 23, 2007 Share #28 Posted February 23, 2007 LCT-- Take the lens off the body and set the body aside. Set the lens down on its front end with the cutout toward you through which the focus tracking roller rides the focus cam. Do the same with a non-CL lens. Now look at the parts where the chrome bayonet ring is cut away for rangefinder tracking. In the CL lens you will find a sloped brass surface there; in the M lens you will find a flat surface there. (BTW--you do a nice job of shooting the interior of the camera. What kind of macro setup do you use--lens, flash etc?) --HC Link to post Share on other sites More sharing options...
lct Posted February 23, 2007 Share #29 Posted February 23, 2007 ...On a sloping cam, the center part of the cam is aligned to give accurate focus... ...look at the parts where the chrome bayonet ring is cut away for rangefinder tracking. In the CL lens you will find a sloped brass surface there; in the M lens you will find a flat surface there I know this my friend but look at my pic above if you don't mind. You agree that what we see there is the sloping cam of the lens (a Summicron-C 40/2) don't you ? If so, you agree also that this cam turns when one focus the lens, right? Then could you explain your first quote above? I don't understand how the center part of the cam may be aligned to give accurate focus. Thanks. Link to post Share on other sites More sharing options...
lct Posted February 23, 2007 Share #30 Posted February 23, 2007 ...What kind of macro setup do you use--lens, flash etc?. Sony DSC-V1 in macro mode & built-in flash. Link to post Share on other sites More sharing options...
ho_co Posted February 23, 2007 Share #31 Posted February 23, 2007 You agree that what we see there is the sloping cam of the lens (a Summicron-C 40/2) don't you ? Unknown. When you move the focusing tab on the lens, does the part of this helicoid that you have marked with red arrowhead come under the cam tracking roller? I seem to recall that the C lenses had a very short focus throw, and this part of the helical wouldn't reach the cam tracker. In that case, this section is obviously not part of the focusing cam. ... this cam turns when one focus the lens, right? This portion of the helicoid rotates when one focuses the lens. I don't understand how the center part of the cam may be aligned to give accurate focus. Perhaps I've confused you. I should have said that the cam tracking roller must be centered for CL lenses, and that the C lens cam is positioned to expect that the distance be read by a tracker centered in the lens opening. Imagine a 4 cm line at 45°, running from lower left to upper right. Imagine a sensor above that line, designed to read information by contacting that line. Imagine that the sensor is currently resting on the center of the line. If you move the line leftward, the height of the sensor will rise. If you move the line rightward, the sensor will drop. This is the case even though the line has been moved sideways and not up or down. In this scenario, when the line is in its original centered position with relation to the sensor, it is supposed to be supplying accurate information. When it is moved left or right, the line no longer supplies accurate information. Now imagine a 4 cm horizontal line, again with a centered sensor. Now with this flat line, moving the line left or right will leave the sensor position unchanged. With this "flat cam," the relative location of cam and cam tracker makes no difference. Focus distance is transferred by the front-to-back motion of the cam only. --HC Link to post Share on other sites More sharing options...
lct Posted February 26, 2007 Share #32 Posted February 26, 2007 The roller cam moves up and down when one focus the lens anyway. It does so with all lenses, no matter is they have a sloped or flat cam. Simply, with C lenses, it does so more quickly or, if you prefer, on a shorter distance because of the slope of the lens cam. In that there is no visible difference between the roller cam of the Leica CL and those of my M cameras (M3, M4-2, M6J) and even of Epson's as clear as i can see. All those bodies give good results with my 3 (!) copies of the Summicron-C 40, despite its sloping cam. Funnily enough the only lenses with which i've got focusing issues have a flat cam, including the M-Rokkor 40/2 for Minolta CLE. Hence my doubts my friend. Thank you for this interesting discussion though. Link to post Share on other sites More sharing options...
ho_co Posted February 27, 2007 Share #33 Posted February 27, 2007 The roller cam moves up and down when one focus the lens anyway. It does so with all lenses, no matter is they have a sloped or flat cam. Simply, with C lenses, it does so more quickly or, if you prefer, on a shorter distance because of the slope of the lens cam. You are correct. That is one of the reasons that Leica chose to use a sloping cam on the C lenses. But as I see it, this has nothing to do with the topic. In that there is no visible difference between the roller cam of the Leica CL and those of my M cameras (M3, M4-2, M6J) and even of Epson's as clear as i can see. I take your word for it. In fact, I would not anticipate that anyone who wanted a product to work with Leica M Lenses would change the design of the focus tracking roller. All those bodies give good results with my 3 (!) copies of the Summicron-C 40, despite its sloping cam. Since your three bodies comprise less than 25% of M bodies made, this statement corroborates my point. How many copies of the Summicron-C you've tried doesn't really matter, because if a body works with one sloped-cam lens, it will work with another. The discussion has to do with M bodies which do not work with C lenses due to an off-center cam tracking roller. Funnily enough the only lenses with which i've got focusing issues have a flat cam, including the M-Rokkor 40/2 for Minolta CLE. That's ironic! But unfortunately, for that you need a repairman. Hence my doubts my friend. To my mind, nothing you have said here has any bearing on the issue I was addressing. LCT-- You have asked: What is an off-center cam roller? What difference does it make whether a cam roller is centered or not? Isn't this the sloping cam? How can the center part of a cam be aligned to give accurate focus? I have answered all these questions to the best of my ability. My original proposition was that some M bodies will not accurately focus a C lens due to not having a centered tracking roller, which is presupposed by the sloped-cam design. If you still have questions in that regard, I am certain that someone else on the forum can explain it better than I. Best wishes! Respectfully, --HC Link to post Share on other sites More sharing options...
Alberti Posted October 15, 2010 Share #34 Posted October 15, 2010 Hi Howard, I bought a Minolta M-Rokkor 40mm last week at the Maison du Leica in Paris. I tested the lens by taking a picture at closest (80 cm) and medium (3m) distance and evaluated the results on my PC: tack sharp. The lens does have a flat focus cam, just like my Leica lenses. attached foto's of the lens cams: first 40mm M-Rokkor then the 50 mm Summicron. From the reflection you can see these are both flat surfaces. - There might be a difference in earlier (CL?) and later (CLE?) versions; my sn# is 2103053. albert Welcome, dear visitor! As registered member you'd see an image here… Simply register for free here – We are always happy to welcome new members! Link to post Share on other sites Simply register for free here – We are always happy to welcome new members! ' data-webShareUrl='https://www.l-camera-forum.com/topic/16365-40mm-mrokkor-on-m8/?do=findComment&comment=1472620'>More sharing options...
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