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Re: Why does light pass through a lens?

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  • Guy Glorieux
    ... I ve tried to find funny answer but I just couldn t. So here are some thoughts. 1. You d get an image with a tiny white imageless hole in the center.
    Message 1 of 21 , Jan 1, 2009
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      Ahah! So what kind of an image would you get if you drilled a pinhole in
      the center of a glass lens?

      Greg

      Oooops!   A pinholed lens?

      I've tried to find funny answer but I just couldn't.  So here are some thoughts.

      1.  You'd get an image with a tiny white imageless hole in the center.  This is because the thickness of the glass lens would prevent a pinhole image to actually form. The reason we use extremely thin brass shim in which to drill the pinhole is to ensure that the vignetting arising from the thickness of the shim is reduced to a minimum.

      2.   If you could design an extremely thin glass lens and drilled a pinhole in the center, then you would have two images that should normally perfectly overlap since the lens focal length would be identical to the focal length of the pinhole.  However, since each lens will have their own distortion features, the pinhole and the lens will not produce identically configured images. 

      3.   Evidently, the pinhole image would be washed out completely by the lens image since the effective aperture of the pinhole would be far less than that of the lens.

      Some have reversed the question:  what if you put a lens in from (back) of a pinhole?  I'll let you figure that one out, if you can...  -:)

      Happy New Year!

      Guy
    • Chris
      Some have reversed the question: what if you put a lens in from (back) of a pinhole? I ll let you figure that one out, if you can... -:) Then it is a
      Message 2 of 21 , Jan 1, 2009
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        “Some have reversed the question:  what if you put a lens in from (back) of a pinhole?  I'll let you figure that one out, if you can...  -:)”

        Then it is a normal camera with a stopped down lens.

         

        Chris

         


        From: owner- photoforum@... [mailto:owner- photoforum@... ] On Behalf Of Guy Glorieux
        Sent: 01 January 2009 17:10
        To: List for Photo/Imaging Educators - Professionals - Students
        Subject: Re: Why does light pass through a lens?

         

         

         

         

        Ahah! So what kind of an image would you get if you drilled a pinhole in
        the center of a glass lens?

        Greg

        Oooops!   A pinholed lens?

        I've tried to find funny answer but I just couldn't.  So here are some thoughts.

        1.  You'd get an image with a tiny white imageless hole in the center.  This is because the thickness of the glass lens would prevent a pinhole image to actually form. The reason we use extremely thin brass shim in which to drill the pinhole is to ensure that the vignetting arising from the thickness of the shim is reduced to a minimum.

        2.   If you could design an extremely thin glass lens and drilled a pinhole in the center, then you would have two images that should normally perfectly overlap since the lens focal length would be identical to the focal length of the pinhole.  However, since each lens will have their own distortion features, the pinhole and the lens will not produce identically configured images. 

        3.   Evidently, the pinhole image would be washed out completely by the lens image since the effective aperture of the pinhole would be far less than that of the lens.

        Some have reversed the question:  what if you put a lens in from (back) of a pinhole?  I'll let you figure that one out, if you can...  -:)

        Happy New Year!

        Guy

      • karl shah-jenner
        ... but it exists in all three common phases on earth ! ;) ... LCD s use polarizing screens, and the liquid crystals are polarized in such a way as to be
        Message 3 of 21 , Jan 1, 2009
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          Herschel writes:

          > This is like the question "Why is water liquid, and not gas, on Earth ?"

          but it exists in all three common phases on earth ! ;)


          >
          > I think the molecular properties that make a substance opaque or
          > transparent may be better understood by looking at the way liquid
          > crystal shutters and displays work. By applying an electrical charge to
          > an otherwise opaque panel we can reorganize the structure and make it
          > transmit light.


          LCD's use polarizing screens, and the liquid crystals are polarized in such a way as to be perpendicular to the polarizing screen, blocking all light.

          under normal conditions the liquid crystals transmit light whether polarised or non-polarized.. effectively they are an electronic shutter :)
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