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Find the magnification of a Keplerian te...

Find the magnification of a Keplerian telescope adjusted to infinity if the mounting of the objective has s diamter `D` and the image of that mounting formed by the telescope's ocular has a diameter `d`.

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In the Keplerian telescope, in normal adjustment, the distance between the objective and eyepiece is `f_(0) + f_(e)`. The image of the mounting produced by the eyepiece is formed at a distance `v` to the right where
`(1)/(s') - (1)/(s) = (1)/(f_(e))`
But `s =- (f_(0) + f_(e))`,
so `(1)/(s') = (1)/(f_(e)) - (1)/(f_(0) + f_(e)) = (f_(0))/(f_(e) (f_(0) + f_(e)))`
The linear magnification produced by the eyepiece of the mounting is, in magnitude,
`|beta| = |(s')/(s)| = (f_(e))/(f_(0))`
This equals `(d)/(D)` according to the problem so
`T = (f_(e))/(f_(e)) = (D)/(d)`.
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