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Basically I'm trying understand the limitations of using the pin-hole model for a camera.

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  • $\begingroup$ The focal points are on the image plane. If they are not, then you won't get a well focused image. A pin hole is not a focal point. $\endgroup$
    – CuriousOne
    Aug 7 '16 at 18:30
  • $\begingroup$ Thank you for the response, I see the error in my thought process. I'm doing computer vision and I'm trying to determine the angle to an object being imaged, from the image plane. $\endgroup$
    – user126638
    Aug 7 '16 at 18:49
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In thin-lens optics, one often assumes that the center of the lens (whose faces by symmetry are locally perpendicular to the line of sight) does not refract light from distant objects, so one can ray-trace from the source to the image plane a straight line through that central point. It requires more calculation to ray-trace rays that hit the lens off-center, and it is only by doing that off-center ray tracing that one can determine the focus (focal point, and focal plane) of the lens.

For a pinhole "lens", it's all about the central point, of course. So there is no off-center light to be traced, no determination of a focal length (to the central focal point, for an image at infinity) or other focusing properties.

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