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Ideal optical collimation system

  1. Oct 20, 2011 #1

    I have been stuck on a project that I am working on. I am trying to collect light using optics from a FOV of 200x200mm at 200mm distance. I have two major problems:

    1. My detector is small so I need to collimate the light (my application is not imaging so I don't worry about the image), I need to reflect that FOV to a detector that is 2.5x2.5mm in size.

    2. I need to block Sun out. I am using an optical filter but these filters are bad when it comes to angle of incidence.

    Let me describe my current system. I have a cheap fresnel lens that has a 5mm FL and 10mm diameter. I use this to collect more light and send to detector and I put a filter in front of this Fresnel lens. The problem is the filter is not enough, It blocks sun ok however there is still quite a bit of sun comes in and introduces Shot noise. I like to make the light collimated so that I can pass through a very narrow band pass filter and kill the sun's impact almost all the frequencies except what I am interested.

    I have considered ideas such as tapered rod, but this has the same problem as my current system. I need optics to make light collimated and parallel. Any ideas or pointers?

  2. jcsd
  3. Oct 20, 2011 #2
    Perhaps there is a language barrier but I really don't know what you are trying to say. You are trying to image something 200x200 mm to a detector of some kind that is 2.5x2.5 mm? Or is collimated light coming through an aperture that is 200x200 mm at a 200 mm distance, and you want to reduce the beam as in a telescope? You need to reflect a field of view, than in some way does or does not contain sunlight? The angle of incidence somehow affects whether or not a filter works? Perhaps if you included a sketch it would be clearer what you are trying to do.

  4. Oct 20, 2011 #3
    I used to make telescope optics, and we used a flat mirror in front of our scopes to autocollimate them. What I gather is that you have a lens focusing light on your sensor, but you'd like to collimate it near focus so that it is a compact beam. I think the simplest way to do this is place a lens near the focus. You might get away with using a telescope eyepiece, but if not you should be able to use the basic thin lens equation to find the focal length you need.
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