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Intricate lens conversion project a'la Rørslett

Discussion in 'Lens Lust' started by Harry S., Mar 24, 2005.

  1. This post is primarily aimed at Bjørn Rørslett, but he suggested to discuss this topic on-forum so anybody is welcome to chime in with good ideas. I mentioned this topic several times at DPR but nobody wanted to bite.

    For those who don't know what this is all about, here's a short summary of what Bjørn describes on his website:

    Cinelenses of old 8mm or 16mm film cameras have astoundingly good optics and, some of them, extremely short focal lengths. However, that doesn't mean that they behave like fisheyes, because of a limited angle of view. Therefore, you don't have to cope with the distortions of usual 35mm WAs. The advantage of such lenses are the very short minimum focus distance and an incredible DOF. The crucial part is the very small image circle, therefore, and also to achieve infinity focus, the use of a relay lens to magnify the image to cover the sensor or film, is a must. The fact that the viewer image stands on its head is a minor disadvantage.

    Once you get this contraption working you are rewarded with breath-taking perspectives, but to get this far you have to be a die-hard DIY-er because you need a few adapters which are hard to come by.

    Here's actually, where my questions come in and where I adress Bjørn ad personam:

    I have two such lenses: a Schneider-Kreuznach 5.5mm 1.1.8 (from an 8mm cam), and a Kern-Switar 10mm 1:1.6 (from a 16mm cam).

    Bjørn, you had developed 2 solutions which I will discuss separately:

    Mark I: you used a reversed WA on a bellows to achieve the necessary magnification ratio. That sounds easy – I will probably try to achieve the same thing with extension tubes.
    But – how did you focus the relay lens on the cine lens? It is difficult enough to find an adapter from a lens thread to a filter thread (in my case M42 or M39 to 52mm. - a custom made adapter from D-or C-mount to M42 or M39 is not a problem), but this still does not enable me to focus.

    MarkII: you use a focusing stage made from a Pentax focusing ext.ring. Did you make this by yourself, in particular mounting the M39 thread to accommodate the Macro-Nikkor? Can this also be made from a focussing helicoid of an old lens?
    At the moment I still prefer the first version because for the second one I would have to sacrifice one of my Photars, which I need quite often for my macro work.

    General question: What aperture do you set on the relay lens? Wide open or at the peak performance?

    I know a company in U.K. who produces custom-made adapters for decent prices (srbfilm) but if anybody knows of additional suppliers, it would be welcome.

    I hope I have not overwhelmed you and any input will be highly appreciated.
  2. nfoto

    nfoto Guest

    "how did you focus the relay lens on the cine lens? ". Easy. The cine lens is mounted on an outer sleeve, while the relay lens moves independently inside.

    As to the Mk.II, the principle is the same, because the macro lens is mounted inside the focusing helicoid, but able to move along when the focusing extension ring is rotated so as to achieve proper focus.

    You need an ample supply of step-up/down/bayonet rings and a little ingenuity to accomplish the task, but the search for a good solution is half the fun of such projects.

    I may locate and show some shots of the details of the various assemblies as soon as I find out how to post images on this forum.
  3. Thanks for the quick reply!

    Expected something like that.

    Exactly! As for the odds and ends supply - I have plenty. I work in a museum, and characteristically, nothing is thrown away in such a place :lol:

    Looking forward to that. If your website allows direct linking, then it shouldn't pose any problem.

    Concerning your website: I remember that some people critisized the messy structure and that navigation is a headache. Well, to some extent this may be right, but on the other hand I like to visit places where I can still find some hidden corners with unexpected information I have not seen before. I like it as it is, but I am a research biologist like you (have been) and for most of us a certain degree of chaos is necessary to keep the brain active :wink:

    Thanks again
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