That is why it is a "Preset" lens. You preset the aperture you want to use, with the one ring. Then you can open the lens for brighter focusing, then slide it into stopdown, to your preset aperture. Nice that you can do it while looking through the camera, very quick. That's about it.
Brilliant! Makes complete sense. Thank you, Nokton.
fbf - For the standard mount Viso lenses (i.e. lenses like the 135mm or the 90mm that can be used either as Viso lenses or as standard lenses attached directly to a Leica body,) you need the focusing helical and the lens mount adapter. The focusing helical is the semi-confusing part, but this is a good website for beginning for puzzling it out.
http://elshaw.tripod.com/Visoflex/Visoflex.html
I suggest printing out the little diagram towards the bottom entitled "Combinations w/the Visoflex III". That's pretty helpful.
For the other type of lens, the short-mount Viso lenses, you just need the lens mount adapter. The 200mm Telyt is a short mount lens.
Cameraquest has a pretty decent break-down on which lenses are which.
http://www.cameraquest.com/viso4.htm
And there is a difference between LTM Viso lenses and M-Mount Viso lenses. Both have the typical mounts as per their names, but they won't mount directly to a camera body due to flanges, and if they could be mounted, wouldn't focus properly due to the missing chunk of the Visoflex body.
Kinda nuts, but the image quality is pretty durn good. Of course, you could just go out and get a Leicaflex and some lenses for the same or better results, but that would require actual money.
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