jev Posted February 16, 2018 Share #1 Posted February 16, 2018 (edited) Advertisement (gone after registration) Hi I am probably missing something I have Leica CL with M Adapter since I shoot mostly with my M lenses, I also had some additional adapter from Rollei QBM to M Recently I bought Carl Zeiss Planar 50mm f/1.4 HFT Lens for Rollei QBM (made in West Germany) wonderful lens in itself, now when I mounted it on Leica CL everything works well, infinity and so on. But there is something strange instead for focusing at 0.45 meters it focuses may be at half of that distance or less, so to to some extend it bevies behaves like a macro/close focus lens Can someone please explain what is going on ? I definitely do not mind but I am just very curious Sample photo attached shot into the mirror Sincerely Eugene 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! Edited February 16, 2018 by jev Quote 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/281891-strange-lens-behavior/?do=findComment&comment=3462922'>More sharing options...
Advertisement Posted February 16, 2018 Posted February 16, 2018 Hi jev, Take a look here strange lens behavior. I'm sure you'll find what you were looking for!
Jared Posted February 16, 2018 Share #2 Posted February 16, 2018 It's because you are using a mirror. With a mirror the focus marked is going to be twice the distance to the mirror itself. Try it with a physical object and I suspect you will find the 0.45m is correct--that's about the distance you would need at minimum focus. Quote Link to post Share on other sites More sharing options...
jev Posted February 16, 2018 Author Share #3 Posted February 16, 2018 Not not really First shot is done at minimum distance with Noctilux Second one minimum distance on Planar I understand that there are differences in minimum focusing, but not that extend 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! Quote 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/281891-strange-lens-behavior/?do=findComment&comment=3462958'>More sharing options...
Jared Posted February 16, 2018 Share #4 Posted February 16, 2018 I think you have just proven that the minimum differences are that significant. The minimum focus distance on the Noctilux is about one meter, yes? And the minimum focus distance is a little under half a meter for the Planar? That means your subjects should appear a little over twice as large in the Zeiss lens. If I just measure the inches across on my monitor of the M9 in the two samples, the image with the Zeiss Planar is about nine inches in width. With the Noctilux it's about 3.75" in width. That's roughly 2.4x smaller than with the Zeiss. If they were really both exactly 50mm in focal length and their minimum focus distance were marked exactly correctly it should have been a factor of 2.2 rather than a factor of 2.4, so it's off by about ten percent. That leaves a couple of possible explanations--assuming my rough screen measurements are vaguely accurate. The actual explanation may be a combination of these. First, it is possible that the actual focal length of either lens is different by a few millimeters from the marked focal length. Nobody sells a 52mm lens, for example, because it isn't a round number, but there are plenty of 50mm lenses that actually are 52mm in focal length. Perhaps the Zeiss is a bit longer than marked. That wouldn't be weird. Or perhaps the Noctilux is a bit shorter. You could do an internet search to see if anyone has calculated the actual focal length of each. The second explanation--and this is probably the larger piece--is the bellows effect. As you focus lenses closer and closer the focal length actually increases. Normally this matters to photographers because you need to compensate for the f/stop. You see this a lot with macro lenses. Lots of cameras will actually show the f/stop changing as you focus closer and closer. It's because the focal length is changing, not because the diameter of the opening is changing. Since the Zeiss focuses closer, it's going to have more of a bellows effect than the Leica. That could easily add up to 5mm of additional focal length at 0.45m which is all you would need to explain the discrepancy. Mostly, though, the lenses are behaving as you would expect. The Zeiss really should be creating images that are about 2.2x larger than the Leica lens, and it's only at 2.4. Bellows and/or focal length discrepancies can easily account for the difference between 2.2 and 2.4. 2 Quote Link to post Share on other sites More sharing options...
jev Posted February 16, 2018 Author Share #5 Posted February 16, 2018 (edited) Jared, Thank you for explanation, now it makes sense I guess it's additional bonus of having full frame & CL is a bit of macro capability on CL BTW I measured the distance for minimum focus with Planar on CL its about 27cm, so i guess lenses really vary a lot from what is written on the barrel Eugene Edited February 16, 2018 by jev Quote Link to post Share on other sites More sharing options...
Jared Posted February 17, 2018 Share #6 Posted February 17, 2018 They do vary quite a bit, but 27cm seems pretty dramatic. You sure you were measuring correctly? It should be from the focal plane of the camera, not from the front of the lens. Focal plane of a CL is about 2cm inside the camera from the flange. You could measure from the front of one of the two top dials and you'd be moderately close (well within a centimeter). Quote Link to post Share on other sites More sharing options...
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