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Asked in GSEB Board July 2022 · Telescopes
Given: fₒ=100 cm, fₑ=1 cm, normal adjustment.
Idea: for the final image to be at infinity, the objective's real image must fall exactly on the eyepiece's first focal plane.
That image lies fₒ behind the objective, and the eyepiece must then stand fₑ beyond it.
L=fₒ+fₑ=100+1=101 cm
So the tube is just over a metre long and magnifies (100)/1=100 times — the length buys the magnification.
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