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I know the magnification of a telescope is fo/fe. But this equation is based on the setting that we put the eyepiece a focal length away from the real image of the objective. Why does we form the final image at infinity? Can we adjust the eyepiece, so that we can have a different magnification? Can we have an even larger magnification than fo/fe?

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The eyepiece acts like a magnifying glass forming a virtual image of the intermediate image produced by the objective

If the intermediate image is placed between the focus of the eyepiece and the eyepiece itself a larger magnification is produced being a maximum when the final virtual image produced by the eyepiece is at the near point of the eye.

Such an arrangement puts a strain on the eye as compared with having the final image at infinity when the eye is relaxed.

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  • $\begingroup$ So... you could theoretically do so for a slight magnification boost with the cost being straining the eye with some additional focussing work? $\endgroup$ – TheEnvironmentalist Nov 6 '18 at 7:15

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