Do Cirkut cameras rotate around the aperture of the lens?

Discussion in 'Panoramic Cameras and Accessories' started by BetterSense, Sep 30, 2009.

  1. BetterSense

    BetterSense Member

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    I'm building such a moving-film-slot-type panoramic camera out of a 35mm camera. I figure I can then print the negatives with my 4x5 enlarger. I was going to have the camera rotate with the aperture at the center of the rotation. It seemed the obvious way to do the calculations, but looking at currently existing cameras, it doesn't look like they do. It kind of looks like the cirkut cameras, both the aperture and the film plane trace out circles. In my design, the aperture would be stationary and the film would move around it.

    Also, what is a good lens focal length for this type of camera? I only have a 50mm lens for this camera. I think the vertical angle-of-view should be pretty good actually. Are lenses for these cameras of the "long", "normal", or "wide" family?
     
  2. jamie young

    jamie young Member

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    cirkuts don't move around the aperture. They do usually take into account the position of the nodal point. I don't know the science of it though. With longer lenses the rotation point is pretty far off the aperture point on a cirkut
     
  3. Bruce Watson

    Bruce Watson Member

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    Yes, one would think they would rotate around the rear nodal point for the lens in question.
     
  4. BetterSense

    BetterSense Member

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    What is this "nodal point"?
     
  5. polyglot

    polyglot Member

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    Not knowing much about a Cirkut except that it's a panning camera, I'm assuming that the lens rotates in space and there's a film transport that runs at the same time to expose a slit continuously... which means the lens would need to rotate about its FRONT nodal point so as to not change perspective throughout the scene. Same principle as used when stitching photos - you rotate about the front nodal point so as not to introduce parallax errors. The rear nodal point is relevant only with respect to the details of the film transport.

    Definition of Nodal Points.
     
  6. Mike1234

    Mike1234 Inactive

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    BetterSense, the nodal point is where all the light converges at the smallest point... where the rays cross over each other near the center of the lens. The aperture is usually centered there.
     
  7. godi

    godi Member

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  8. BetterSense

    BetterSense Member

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    Regardless of what it's called, I think I now understand that I should position the camera with respect to the pivot such that there is no perspective change when it rotates. With an SLR, this should be easy to determine by experimentation. It looks like my design will be stuck with a normal 50mm lens.
     
  9. Mike1234

    Mike1234 Inactive

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    You can often find the diagrams of lenses online. It's fine if you get pretty close.
     
  10. BradS

    BradS Member

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    ...and if you're not close, you get more interesting photos!
     
  11. clay nz

    clay nz Member

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    In theory any rotating camera should rotate around the lens nodal point but Cirkuts prove the rule can be ignored and produce acceptable results.

    Clayton
     
  12. godi

    godi Member

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  13. c.d.ewen

    c.d.ewen Subscriber

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  14. Bruce Watson

    Bruce Watson Member

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    I stand corrected. Entrance pupil it is.
     
  15. Janos

    Janos Member

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    Where the light enters the lens, at the front element, is the front nodal point. Where it exits, is the rear nodal point. The centre, where the light crosses at a central point, where the aperture should be, is also a nodal point- could be called the cardinal point. I think you want to pan the camera around the cardinal point. I'm sure there are some which have been designed to do this, but I'm pretty sure that's not the case with the old Horizont which I had once. Irrelevant on this sort of camera anyway, as the image won't require stitching, unless you are operating 3 cameras back to back, as they once did at the peak of Mt. Everest, with three panon wideluxes. It was a clear day too. I don't know where you can find this image, sorry.