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Distant objects imaging

  1. Jan 30, 2009 #1
    A telescope takes an image of a distant terrestrial object,lets say a tree, and amplifies and broadens it; however i ask myself if is not posible to build with some combination of lenses an apparatus where you will see an image of the distant object as IF YOU WERE NEAR OR CLOSE TO IT, this app would be different from a telescope i think ;does such artifact exists or can be built?
     
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  3. Jan 30, 2009 #2

    mgb_phys

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    Isn't that what a telescope does?
     
  4. Jan 30, 2009 #3

    russ_watters

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    The only difference I can think of between being closer and using a telescope is perspective, and if that's what you are getting at, no, it isn't possible to manipulate perspective with lenses.
     
  5. Jan 30, 2009 #4
    I am not really sure of your question.

    A telescope really does not 'amplify' a distant object. It take the apparent area and expands it over the area you are viewing.
    This is why as you increase the 'magnification' the object seems to become dimmer.

    You can not add more light or detail into a distant object than already exists. As for perspective. as all ready pointed out it can not be manipulate with a lens.

    Perhaps you could be more explicative in you question. :-)
     
  6. Jan 30, 2009 #5

    marcus

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    Suppose you would remove the restriction that it be done entirely with lenses and allow digital optics, or virtual reality goggles.

    The idea might be to make it seem as if the planet Jupiter, or the Whirlpool Galaxy filled an entire wall at an airport or other public building. And you could walk around and view it from different perspectives.

    Is this not what you had in mind? If not, could you say more explicitly?
     
  7. Jan 31, 2009 #6
    well,let me change the question to: ¿how can you differentiate an image from a distant object ( ex a tree) taked with a telescope, and an image of the same tree taked with a normal camera but taked from a near distance , in such a way that the tree image size in both cases is the same?
     
  8. Jan 31, 2009 #7
    OK , I think I understand now. Someone may correct me on this, but I think the difference would be in the resolution.

    If I point my scope at a terrestrial object and capture a picture under magnification I am narrowing down the field of view. In doing this I loose information. The resolution of the picture decreases proportional to the magnification.

    However, if I am near the same object and take a photo, more of the actual area of the picture is resolved. Good old three dimensional space.

    An analogous instance would be if you took a picture of lets say of a news paper at 3 meters. The picture would be a relative good representation of the news paper. How if at 3 meters I took the photo through the scope, the resolution wold be substantially less because of the field of view.
    In fact if the magnification was enough I may resolve the photo into the individual ‘dots’

    Also, if the field of view is decreased the available light is also ‘spread out’.

    This is why dim objects are much better viewed through a large apatura instruments rather that using high magnification.

    The same rule applies to your visual of a tree being at the point or through magnification.
     
  9. Jan 31, 2009 #8

    mgb_phys

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    For a two dimensional scene there is no difference.
    If you stand 1m from an object and take a picture with a scene 1m*1m, then step back to 10m and with a longer focal length take a picture of the same 1m*1m at the object then (assuming no intervening atmospheric effects) there is no difference.

    In a 3 dimensional scene (with depth) then the perspective and depth of field (how much in front and behind the object are in focus) do depend on the focal length (ie magnification) of the lens. You use this effect in photography to allow you to isolate an object from a confusing background.
     
  10. Feb 1, 2009 #9
    Quick question here. I could be interrupting this wrong (would by no means be the first time).

    If I stand 1 meter from an object and take picture, then step back 10 meters and take the same picture. The two picture would look relatively the same. However, I am under the impression the 10 meter picture would contain less resolution. Simply because the use of a longer focal length has in essence expanded the space I was photographing in the first place thus reducing the resolution.

    My knowledge of photographic optics are somewhat limited so this is not an argumentative point. Just a bit more explanation would be appreciated.

    Thanks
    Ron
     
  11. Feb 1, 2009 #10

    russ_watters

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    Assuming the lens was what limited the resolution (as opposed to the film/ccd), a zoom lens that is zoomed-out at 1 meter and set to magnify 10x at 10m would, in fact, produce a lower resolution image. The resolution (angular) of a lens is a function of its aperature.
     
  12. Feb 1, 2009 #11


    The lens (and quality of) will always be the limiting factor angular or other wise., whether 20 - 35 mm, or 20 -200 mm or X - X mm, even a 'T' ring adapting to the scope, irrespective of the focal length.

    The aperture is always an integral factor in resolution;( don't want to get into a 'bunch' of math here).

    To coin a phrase " Bigger is better' as aperture goes.
    There is no argument here.
    Basic physics in optics.

    Merci, I much appreciate your comment russ_watters.
     
  13. Feb 2, 2009 #12
    Surely what japam is looking for is a stereo camera. He's only talking of terrestrial objects
     
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