* It is very well known to most of the students, that astronomical telescope produces final image inverted with respect to the original object. So overall magnifying power is of negative sign.
*To overcome this defect, two telescopes have been proposed , one called terrestial telescope and second one Galelian telescope. The terrestrial uses another converging lens placed between the objective and eyepiece . This lens simply inverts the intermediate image without numerically modifying magnifying power.Introduction of this third converging lens increases the length of the instrument by 4 F where F is the focal length of the third lend introduced between the objective and eyepiece. This third lens is so adjusted that the image formed by the objective lies at the 2F point of the third lens to be introduced.
*To overcome this defect, two telescopes have been proposed , one called terrestial telescope and second one Galelian telescope. The terrestrial uses another converging lens placed between the objective and eyepiece . This lens simply inverts the intermediate image without numerically modifying magnifying power.Introduction of this third converging lens increases the length of the instrument by 4 F where F is the focal length of the third lend introduced between the objective and eyepiece. This third lens is so adjusted that the image formed by the objective lies at the 2F point of the third lens to be introduced.
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