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I did a homework problem in which I was to show that a refracting telescope, modelled as a sequence of two thin lenses separated by a distance equal to the sum of their focal lengths, is capable of producing angular magnification. In my course we have been solving these questions in geometric optics by modelling a paraxial ray as a vector consisting of its perpendicular distance from the optical axis at a given point, and the angle between it and the optical axis: [itex] (y, \theta) [/itex].

The effect of the optical system on this ray was then ascertained by deriving the ray matrix for the telescope, which was simply a cascade of two thin lens ray matrices and one free space propagation matrix. My solution did indeed show that the telescope produced angular magnification. The homework solutions went on to state that angular magnification is, "the most relevant magnification in the imaging of distant objects." My question is simply, why is this true, why is the magnification of [itex] \theta [/itex] important, more so than magnification of y?

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# Ray Optics: Angular Magnification

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