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Henry · Posted: Mon Feb 29, 2016 3:03 pm Post subject:

Yes, Dan, I was beginning to suspect the same. One thing for sure: the 203 Optar will not work with the Kalart. But the OP did say f5.6 203mm, which should have tipped me off at once that it was the Tele, since the 203 Optar is f.7.7 (IIRC).

Dan Fromm · Joined: 14 May 2001 Posts: 2144 Location: New Jersey

MultiFormat Shooter · Joined: 26 Jan 2016 Posts: 17

Dan Fromm · Joined: 14 May 2001 Posts: 2144 Location: New Jersey

No, from the Kalart RF's point of view focal length is focal length.

The only difference between a tele lens and a lens of normal construction of the same focal length, from the camera's point of view, is where the front standard sits on the bed when the lens is focused to infinity. From the user's point of view, a tele lens will require less extension to focus to infinity so will be a more comfortable fit on the camera.

William Hallett · Joined: 07 Jan 2012 Posts: 101

A Kalart responds to the displacement of the bed from the infinity position. It is not affected by infinity stop placement, because it is actuated by the cam attached to the back of the bed. A telephoto lens moves the same distance to focus on a given object distance as does a regular lens of the same focal length, even though it sits much closer to the film plane. Therefore, if the Kalart won't work with a regular 203 mm lens, it also shouldn't work with a 203 telephoto.
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WilliamH

Henry · Posted: Thu Mar 03, 2016 5:34 pm Post subject:

Then that settles it. My 203 Optar f7.7 (non-Tele) focuses infinity at the far outer end of the bed, way beyond the reach of the Kalart arm. And even if the Kalart did work, I'd always focus with the loupe on the ground glass.

William Hallett · Joined: 07 Jan 2012 Posts: 101

If your 203 can be focussed at infinity with the track all the way back into the case (i.e. the normal position for infinity), then the arm of the Kalart will still be in contact with the cam. The question is how much track movement the Kalart will allow before the cam loses contact with the arm. On my 2x3 Pacemaker Speed this distance is about 15 mm with the Kalart set up for the usual 101 mm lens. That should in theory be enough travel to focus a 203 down to about 10 ft. However, I don't know whether this amount of travel is still available when the Kalart's internal adjustments are changed for a different focal length lens, and I don't know whether the Kalart is actually intended to function properly through all of that 15 mm travel. (For a 101 mm lens, 10 mm travel takes you to the end of the focussing scale at 4 ft, and that may indicate the actual useful range.)
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WilliamH

Henry · Posted: Fri Mar 04, 2016 2:41 pm Post subject:

Sorry, I had it backwards in my previous post. It is indeed infinity focus when bellows draw is short, not long. Oops...