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Eye vs Teloscope

  1. Jun 22, 2011 #1
    Hey guys, just wondering what limits how far an eye can see...

    I understand how an eye works. Light comes though the lens and focus on the retina, which goes to brain for interpretation, etc.

    And I understand the workings of different types of teloscopes. In different ways they gather lots of light and focus it through the eyepiece. I think essentially they collect more light for the viewer.

    But is that all that is different?

    If our eye was as wide as the front lens of a teloscope, would our eyesight be equivalent to a teloscope?
  2. jcsd
  3. Jun 22, 2011 #2
    The eye can see to the edge of the universe if there's a bright enough light.

    The difference between the eye and telecope is three things.

    1) sensitivity aka light gathering power.
    The scope has two advantages. Big aperture and time integration. It can gather more light and can bring in light over hours to fill in even dimmer images.
    2) Magnification. Saturn looks like a dot to the eye. The scope sees rings and moons. That's the most striking difference.
    3) Spectrum. Instruments on the scope can see things the eye can't like UV, IR, radio or even Xrays.

    If the eye was as big it could do 2 and some of 1 but not 3.
  4. Jun 22, 2011 #3
    To answer the specific question of how "far" the eye can see. There is no limit.

    What is the minimum amplitude of radiation that the eye can detect is a different question.
  5. Jun 22, 2011 #4
    Is it worth noting that time (i.e. having enough of it for the light to cover the distance) is a limit?
  6. Jun 22, 2011 #5
    Asking how far can you see is like asking how far can your car can travel. How much gas do I have? How much time I have?
  7. Jun 23, 2011 #6


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    There is another very important factor about a telescope. The diameter is much greater than your eye and so is the 'resolving power'. That is to say, you can see much more detail because of the larger aperture. The extra resolution is at least as important as the extra light-gathering of a big diameter lens.
  8. Jun 23, 2011 #7
    It is a matter of energy conservation and symmetry of space.

    The total energy from the light emitting source is spread over the surface of sphere of radius r = distance from the object. A larger lens is tapping into a larger portion of this sphere.
  9. Jun 24, 2011 #8

    Claude Bile

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    The question is flawed insofar as one must specify the resolution at which one intends to observe said objects in order to receive a reasonable answer.

    To observe a photon from a distant quasar with the naked eye is possible (not that you would know that you had observed it); observing it with any significant resolution is impossible without an outstanding optical system.

  10. Jun 24, 2011 #9


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    I think there is no way of determining the source of just one photon because any optical system relies on diffraction (that is ANY optical system) to form an image. Diffraction involves a (large) number of photons for an intensity distribution to reveal the direction of the source. You would have no way of distinguishing just one photon coming in from the side from one arriving on axis.
  11. Jun 24, 2011 #10


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    I think that was his point sophie. That you CAN detect photons from very distant sources, but that one single photon or even a few cannot form an image. You "wouldn't know you say it".
  12. Jun 24, 2011 #11


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    My point was that there is no "outstanding optical system" that could tell you. All you would know was that a photon had arrived from somewhere. It takes several of them to give any idea at all about their source (if it is a single source even).
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