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Thread: Help setting up a perfect auto framing camera rig for rectangular target

  1. #1

    Help setting up a perfect auto framing camera rig for rectangular target


    I have a situation where simply targeting the camera at a point is not sufficient:

    I have a static rectangular shaped target object (a picture frame), that I have the camera moving about the front of somewhat - perhaps up to 60 degrees either side of, and 45 degrees vertically.

    However, if I simply target the camera to the centre of that rectangular picture frame object, as the camera moves to the extremes of its positioning the framing becomes less than perfect. Although it continues to point to the true centre of the targeted object, a real camera operator would adjust the framing such that the edges of the picture frame remain somewhat equi-distand to the edges of the camera frame, which is not what pointing at a fixed target in the centre of the geometry achieves.

    I've tried at length, using trig and other tricks to produce a rig that correctly targets as the camera moves. But have had no success.

    Can anyone help?


  2. #2
    TrueArt Support
    Join Date
    Feb 2003
    Maybe target at null, and keyframe null positions?

    Or maybe make null child of original target (if it's moving also).
    And fix places that needs fixing, moving up/down null (that'll be relative to original target).

  3. #3
    Don't just target the object, as you have found you lose some control when it comes to framing. The simple solution is to parent a null to that object and target the camera to that null. Now you can adjust the camera framing by moving the null around.

  4. #4
    Super Member spherical's Avatar
    Join Date
    Dec 2004
    San Juan Island
    What Sensei and djw said. Essentially your sequence doesn't match what you expect, because a human camera operator would continually re-frame the shot as the POV changed, in order to have a pleasing frame. What trips up purely mechanical targeting is the chosen focal length of the camera lens. If it is a wide angle and you're in close, objects nearer to the lens will appear large in relation to everything else that is farther away. This inherently changes the framing of the shot. There is possibly a nodal method of approximating the same effect, but adjusting the position of the target null is the most direct way to get a pleasing result; principally because you are the cameraman and choose a pleasing angle as the scene progresses.
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  5. #5
    Registered User Slartibartfast's Avatar
    Join Date
    Jun 2012

    If you like automating stuff and have a node-fetisch, then you might enjoy this scene . Basically it does what is suggested above with a target null, but it's autopositioned. Now, I must clarify that the nodes are NOT optimised at all. I just threw it together as a proof of concept. Hope you can use it.

    Last edited by Slartibartfast; 01-26-2015 at 03:47 PM. Reason: oh... you'll need DPKit (as usual)

  6. #6
    Thanks All.

    In the end I basically drove the position of a target null as a fractional position of the camera movement in both x and y directions. Seems to be working so far.


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