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I Lens aligning various angle of incidence light striking it?

  1. Jun 30, 2016 #1
    Assume a flat one square foot vertical plate attached 6 feet up, outside on a wall.

    Dozens of yards away are various solar reflectors angled to reflect sunlight onto that plate.

    Problem is, the plate requires to be only struck straight on at a 0 degree angle of incidence.

    And, all the reflected sources are striking it at some other angle up to 45 degrees off center.

    Is there any lens or dome or reflective funnel arrangement, or something else altogether, that
    could be put in front of the plate to take all those different angled incoming sunlight sources
    and align them all, to next be exiting it to strike the plate behind it straight on at a 0 degree
    angle of incidence?

    Thank you for any thoughts or suggestions.
  2. jcsd
  3. Jun 30, 2016 #2


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    There's no combination that could make all the light strike at exactly 0 degrees, but a simple negative lens placed near the plate might reduce the angle, making it closer to normal incidence (perpendicular to the plate's surface). I don't know what power or diameter the lens would need to be though.
  4. Jun 30, 2016 #3
    Wonder if somebody has done a stacked arrangement of such lens, to progressively get average of off angles closer to zero?
  5. Jun 30, 2016 #4

    Andy Resnick

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    Only if it is a lossy system, otherwise you violate the first law of thermodynamics (conservation of etendue).
  6. Jun 30, 2016 #5
    Gotcha, thanks for your patience with me.

    I was kinda imagining an optical cone or funnel of sorts, creating a more laminar flow of light as the angles reduced with every reflection, finally approaching 0 degrees. But, each reflection along the way loses a little power, yes?
  7. Jun 30, 2016 #6
    There are such things used by people doing non-imaging optics, e.g. a Winston cone is an example on a much smaller scale than what you need, but yes there is loss at each reflection. Do the rays need to have exactly 0 degree angle of incidence?
  8. Jun 30, 2016 #7
    Thanks for Winston Cone tip, interesting.

    I'm trying to get clarification from two hot mirror manufacturers, in regards to how transmission/reflectance degrades when AOI exceeds 0 or 45. They are optimized for either one or the other and earlier inquiry to Edmunds Optical regarding their UV/IR filters had them respond with; "...the angle of incidence is critical to the performance of the filter. If the angle is off, the efficiency will not be the same as the published specifications." Waiting to hear back now if that applies also to the hot/cold mirrors and exactly how much is too much AOI.
  9. Jun 30, 2016 #8


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    Why does the light need to be at a near-zero angle of incidence?
  10. Jul 1, 2016 #9


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    The devices the OP describes, hot mirror and cold mirror, are interference filters. At off-angle incidence the optical path through the various layers is longer than the needed 1/4 or 1/2 wavelength of light that is needed for destructive or constructive interference. This shifts the wavelength of peak attenuation or transmission away from the design value. Additionally, the further the incident angle is away from the normal, the greater the reflective losses.
  11. Jul 1, 2016 #10


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    Any chance that flat plate can be replaced with a dome-shape to get normal incidence, and place any needed optics behind it?
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