microview Posted December 24, 2012 Share #1 Posted December 24, 2012 Advertisement (gone after registration) Speaking the other day to a Leica aficionado, I mentioned that with both my 35 and 50mm screw-mount lenses on Voigtlander adapters for the M9, when the lens is locked in position the depth scale markings are angled away from a perpendicular axis, a degree or so towards the viewfinder window. He seemed to think everyone knew that (!) but I wonder why they are made like that? Obviously if one slackened the lens to have it at the 12 o'clock position the focus would be slightly adrift. Link to post Share on other sites More sharing options...
Advertisement Posted December 24, 2012 Posted December 24, 2012 Hi microview, Take a look here LTM adapter – I wonder why. I'm sure you'll find what you were looking for!
elgenper Posted December 24, 2012 Share #2 Posted December 24, 2012 For some reason, all lenses did mount in that position on all pre-M bodies (i.e. with screw mounts), so the adapters are made that way, too. A different position would indeed impair the RF coupling, and not seating the lens or adapter properly might even lead to dropping it off the camera. Link to post Share on other sites More sharing options...
250swb Posted December 24, 2012 Share #3 Posted December 24, 2012 Two reasons why the LTM lenses are meant to mount at an angle. The first is that on the LTM bodies mounting an accessory finder could obscure the focus scale, so the lens was mounted off centre so you could see around the finder from above. The second, which applies to M bodies as well, is that the focus throw of the lens begins and ends so your finger doesn't end up in the viewfinder at the closest focus distance. There are Voigtlander adapters that mount the lens square, but true LTM adapters mount it off-centre as the original was supposed to be, and often criticised on camera forums as being bad Chinese engineering on the cheaper but often perfectly accurate 'Ebay Specials'. Steve Link to post Share on other sites More sharing options...
jaapv Posted December 24, 2012 Share #4 Posted December 24, 2012 Other brand lenses like Canon mount that way as well. Link to post Share on other sites More sharing options...
Erik Gunst Lund Posted December 24, 2012 Share #5 Posted December 24, 2012 The mount on the Voigtlander LTM lenses can be rotated. Remove the M-LTM adapter. Loosen and remove the screws that hold the mount, turn the mount and remount the screws. Remount the M-LTM adapter. It's as easy as that... Link to post Share on other sites More sharing options...
!Nomad64 Posted December 25, 2012 Share #6 Posted December 25, 2012 Afraid it's not so simple. You turn the mount and the cam will attack at another angle thus focusing will go berserk. Cheers, Bruno Link to post Share on other sites More sharing options...
Erik Gunst Lund Posted December 25, 2012 Share #7 Posted December 25, 2012 Advertisement (gone after registration) Afraid it's not so simple. You turn the mount and the cam will attack at another angle thus focusing will go berserk. Cheers' date=' Bruno[/quote'] All Voigtlander lenses I have seen has a flat focus cam, so no change at all! I have only seen a slanted focus cam on Leica C lenses. Which Voigtlander lenses have you seen with slanted focus cams? Link to post Share on other sites More sharing options...
!Nomad64 Posted December 25, 2012 Share #8 Posted December 25, 2012 If the focus cam profiles were flat the rangefinder couldn't possibly work. The only flat cams are those mounted on older LTM rangefinder-uncoupled lenses such as the Skopar 21 & 25. Cheers, Bruno Link to post Share on other sites More sharing options...
Erik Gunst Lund Posted December 25, 2012 Share #9 Posted December 25, 2012 No I'm not referring to uncoupled lenses... Take any Voigtlander LTM lens and focus it while it's unmounted, you will see the focus cam rotate and move in and out in axial direction. Inside the lenses are several threaded selves making this movement possible, thats how all rangefinder lenses are made including Leica-M lenses, except for most 50mm which has the correct movement, but that is another story... You apparently have to see it before you believe it... When you remove the threaded mount from the lens after removing the three screws, you will see that there are several sets of threaded holes for attaching the threaded LTM mount at different angles. This has no influence on the focus distance of the lens, but when you remove the mount you will see an other flange locked by three other screws and that is for adjusting the focus distance of the lens, leave those as is, unless you are skilled in the art... Link to post Share on other sites More sharing options...
elgenper Posted December 25, 2012 Share #10 Posted December 25, 2012 Somewhere I have an old and erudite mathematical description of the RF adjustments. Can´t find it, but I recall that a flat cam will work exactly for three distances, and can thus be adjusted to give as small a maximum absolute error as possible by placing these three points (done by adjusting the RF arm length). This did work well enough for the short and slow lenses of the time; to work with lenses like the Summicron 90 or the Noctilux, the cam will have to be ground to a specific curve. Obviously, a flat cam is insensitive to errors in the angular position of the lens (or rather the RF arm roller relative to the lens); a ground one is not. Link to post Share on other sites More sharing options...
!Nomad64 Posted December 26, 2012 Share #11 Posted December 26, 2012 No I'm not referring to uncoupled lenses... Take any Voigtlander LTM lens and focus it while it's unmounted, you will see the focus cam rotate and move in and out in axial direction. Inside the lenses are several threaded selves making this movement possible, thats how all rangefinder lenses are made including Leica-M lenses, except for most 50mm which has the correct movement, but that is another story... You apparently have to see it before you believe it... When you remove the threaded mount from the lens after removing the three screws, you will see that there are several sets of threaded holes for attaching the threaded LTM mount at different angles. This has no influence on the focus distance of the lens, but when you remove the mount you will see an other flange locked by three other screws and that is for adjusting the focus distance of the lens, leave those as is, unless you are skilled in the art... Aye Sir, you're right. Checked better to find that cams aren't slanted and have no need to be, as the distance is set by rotating the helicoid. Therefore the angle of attack is not influent. Cheers, Bruno Link to post Share on other sites More sharing options...
ynp Posted January 12, 2013 Share #12 Posted January 12, 2013 I have an 50-75 ltm adapter, bought with my Rolley Sonnar 40mm, and it clicks into the correct position on my M. All my other ltm-to-M adapters, Kipon and Hansa, mount the lens on the side. it is ok for longer lenses, but the work with the focussing tab/lever became very unintuitive. I want to find a 'straight' version of the 35mm adapter. Do you , experienced Leica users, know where to look ??? Thank you. Link to post Share on other sites More sharing options...
!Nomad64 Posted January 12, 2013 Share #13 Posted January 12, 2013 Try the original Leica or CV. If you badly need the 6-bit coding you may want to try your skills with a Dremel. Cheers, Bruno Link to post Share on other sites More sharing options...
John Black Posted January 20, 2013 Share #14 Posted January 20, 2013 Here is a picture showing the Canon 100mm F2 Serenar LTM rotated about 30˚ off-center: More pix of the Canon 100mm F2 Serenar, etc. here. Link to post Share on other sites More sharing options...
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