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Astronomical Refracting Telescopes produce an image at infinity - which makes no sens Watch

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    When a normal lens receives light from an object at its focal point, there is said to be no image formed, as the rays emerge parallel and only converge at infinity.

    I do not understand why this rule does not seem to apply for astronomical refracting telescopes, as the eyepiece lens should operate under the same rules, and therefore surely not create any image. (In a refracting telescope the the objective lens focuses light from a star to a point, creating a real, inverted diminished image. This image is at the focal point of the eyepiece lens which then creates a magnified virtual image apparently at infinity)

    Why is an image only formed in one of these cases?
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    (Original post by edudog)
    When a normal lens receives light from an object at its focal point, there is said to be no image formed, as the rays emerge parallel and only converge at infinity.

    I do not understand why this rule does not seem to apply for astronomical refracting telescopes, as the eyepiece lens should operate under the same rules, and therefore surely not create any image. (In a refracting telescope the the objective lens focuses light from a star to a point, creating a real, inverted diminished image. This image is at the focal point of the eyepiece lens which then creates a magnified virtual image apparently at infinity)

    Why is an image only formed in one of these cases?
    You answered your own question:

    Light from a star is to all intents and purposes received as parallel rays which are then converged to an image. However, the actual detail the lens can resolve is determined by the diameter of the lens and the wavelength of the light received.

    Light received from an object already at the focal point are not parallel rays entering the lens but emerge parallel from the lens and therefore the image appears to be at infinity.
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    (Original post by uberteknik)
    You answered your own question:

    Light from a star is to all intents and purposes received as parallel rays which are then converged to an image. However, the actual detail the lens can resolve is determined by the diameter of the lens and the wavelength of the light received.

    Light received from an object already at the focal point are not parallel rays entering the lens but emerge parallel from the lens and therefore the image appears to be at infinity.
    But a similar thing happens with telescopes:
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    As you see here, the rays also emerge parallel for a telescope, so surely this would produce the same effect as what you described?
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    (Original post by edudog)
    But a similar thing happens with telescopes:[img]data:image/png;base64,iVBORw0KGgoAAAANSUhEU gAAAToAAACgCAMAAACrFlD/AAAA8FBMVEX////r6+u+vr6enp7i4uIAAAD/AADIyMj/np709PS1tbX/mpr/nJz//Pzu7u7/+fn/o6Obm5v/sLD/oaH/8vL/rKz/2tr/uLj/ra3/xcX/0ND/4+P/7++np6f39/f/5ubS0tLd3d3/wsL/u7v/1NSurq7Ozs7/k5NtbW2SkpKJiYlkZGT/jY1VVVUtLS2AgID/YGD/dnZ4eHg5OTlaWlr/hYX/LS0bGxv/SUlMTEz/OzvmfHz/Ghryi4v/XV3Yb2+9eXm+kpLE09PgxsajAAD/enrUlpb/bGz/RkYWFhbUYmJBQUG+bm6+p6fRfHyhW1uo 6i96AAARMElEQVR4nO1dCZuiSLYNdhDZ FFA2xTUTsyqzqjKra3k9NfNmXk91vXoz 8///zYsQNyCQCEBNuz1ff10pYoDHGzfuFhcA/nS4v/QNXC1YQbr0LVwrHgVBufQ9XCc6giA8Xf omrhOKnuj6pW/iWsFd+gauFzfqauNGXW1cijp+eaELt4f WqPOHPs3pD2/buvDFQEndRBqVvWW4qjMnHYcRhAXdlV8 fKKn78MgeeVdzu7JDNM6DcP22ODF1Izj DuPgn86niPKMrT+3K0RbR0+LaDUpS6pQ PD9KLIDz/TKqd3nGv64UV54w6hBfOYHHP1/kYFfR7i+xEYql77DwI4EeSsB9Izg5mqn +UPaUWdcLk9LN8ZU3ITiSmjn3+9LC45w SB9BPBm/dHZC+l7pjixGAhEP1upciJLIMVYeGRgD r0STIimBiA5+Tnsy7w63E5huRT2vDj11 nJoouoYy3K6acIpes7EWLugBU9YrEi/IFk6UcjEVHHfBBisHp4fqun04zcnNWc7 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    As you see here, the rays also emerge parallel for a telescope, so surely this would produce the same effect as what you described?
    That's exactly what I described.
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    (Original post by uberteknik)
    That's exactly what I described.
    But it seems that for both scenarios (one being the eyepiece lens for the telescope, the other being the isolated lens with an object at its focal point), the light rays that exit the lens are parallel to one another, yet in only one case a virtual image is formed
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    (Original post by edudog)
    But it seems that for both scenarios (one being the eyepiece lens for the telescope, the other being the isolated lens with an object at its focal point), the light rays that exit the lens are parallel to one another, yet in only one case a virtual image is formed
    This may make it clearer (pun intended).

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    (Original post by uberteknik)
    This may make it clearer (pun intended).

    I understand this, and this is pretty much what the objective lens is doing. It's the activity of the eyepiece lens that confuses me though, because the image is at f of the eyepiece lens and therefore the image produced is at infinity with parallel rays. Surely parallel rays means no image is produced at all though because the rays never converge?
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    (Original post by uberteknik)
    This may make it clearer (pun intended).

    Any Ideas?
 
 
 
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