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Thread: Distance measurement

  1. #51
    Senior Member thrice's Avatar
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    Re: Distance measurement

    Am I missing something, isn't the nodal point on any central shutter lens (all lenses on tech cameras other than the FPS) the location of the shutter/aperture?
    I simply use a ruler and line it up with the axis of rotation on my pano head.

    On topic, any laser rangefinders safe to use for close distance portraits? The disto D5 is meant to be 'eye-safe' but that strikes me as a relative term.

  2. #52
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    Re: Distance measurement

    Quote Originally Posted by thrice View Post
    Am I missing something, isn't the nodal point on any central shutter lens (all lenses on tech cameras other than the FPS) the location of the shutter/aperture?
    That is a very good assumption and for a symmetrical design it would be good place to bet on. For a telephoto or reverse telephoto (retro focus), not always.

  3. #53
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    Re: Distance measurement

    Uh, I thought the distance on the focusing ring was from the image plane, not the lens front nodal plane?

    Ie DoF formulas are for the front nodal plane, and the Alpa HPF ring is for the image plane. So when you want to focus spot on you should align the disto with the sensor.

    Concerning the DoF calculator - for longer distances it will be no problem to ignore that the DoF formulas is for front nodal plane rather than the image plane, and for close/macro distances the typical DoF formulas has other errors too and DoF will be so extremely short so it makes not much sense to use it. The distance scale for close focusing works fine though, from the image plane.

  4. #54
    Subscriber Member tashley's Avatar
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    Re: Distance measurement

    Thank you guys. That's what I needed to know.

  5. #55
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    Re: Distance measurement

    Quote Originally Posted by thrice View Post
    Am I missing something, isn't the nodal point on any central shutter lens (all lenses on tech cameras other than the FPS) the location of the shutter/aperture?
    Unfortunately , I could not find corresponding information for any RODENSTOCK or SCHNEIDER lens .
    On this following sheet the pupil position is measured from the film (sensor) plane .
    http://www.hasselblad.de/media/6008/cfi150.pdf
    All the HASSELBLAD V-SYSTEM lenses (except F and FE lenses) have a central shutter but the distance is always measured from the film (sensor) plane and it is not always the position of the shutter .
    Attachment 73307
    In some other CZ documentation , for other lenses , that measurment is given from the front lens.
    Regards . Jürgen .
    -----------------------------------------------------------------------------------

  6. #56
    Subscriber Member tashley's Avatar
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    Re: Distance measurement

    Thanks Jotloob - I will experiment.

    In the meantime I am taking one for the team: here is a table which took me for ever and ever to cut and paste and which gives all the Rodie/Alpa HPF distance markings down to 0.5m so other users of the system with a disto can cut out and keep! The process of getting the data out of Alpa's PDF was a nightmare due to weird formatting issues...

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    Re: Distance measurement

    Quote Originally Posted by torger View Post
    Uh, I thought the distance on the focusing ring was from the image plane, not the lens front nodal plane?
    that's what i thought too

    i always measure the distance from the sensor plane. never heard about measuring from the nodal point...
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  8. #58
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    Re: Distance measurement

    ok, just read in jae moons thread "talking technical on tech cameras" again.
    really couldn't remember most of it

    nodal point and sensor plane are mentioned, but i'm afraid i'm not really getting the point. my understanding of optics is just not good enough...

    but one sentence saved me from frustration:
    jae moon: "It is an industry convention that the object distance is between the sensor plane (not the nodal point) and the object."

    and therefore hpf rings or arca helical are made to do the right thing for you.
    just measure the distance from sensor plane - don't worry about nodal point

    am i getting it right?
    www.thomasebruster.com
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  9. #59
    Subscriber Member tashley's Avatar
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    Re: Distance measurement

    My initial tests seem to indicate that that works - which is all I need to know!

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