Magnifying Power Of Astronomical Telescope Normal Adjustment

Magnifying Power Of Astronomical Telescope Normal Adjustment — the NEET Physics formula with its derivation, variables, validity constraints and worked solver.

Magnifying Power of Astronomical Telescope (Normal Adjustment) This formula applies to a refracting astronomical telescope when adjusted for normal vision, meaning the final image is formed at infinity. This configuration is used for relaxed eye viewing. Angular magnification M is defined as the ratio of the angle subtended by the image at the eye (beta) to the angle subtended by the object at the unaided eye (alpha). Since the object is at infinity, the objective lens forms an image at its second focal point, at a distance f o. For normal adjustment, the eyepiece is positioned such that this intermediate image lies at its first focal point, forming the final image at infinity. Using geometry and small angle approximation, alpha approx tan(alpha) = h/f o and beta approx tan(beta) = h/(-f e). Dividing beta by alpha yields M = -f o/f e. The object must be effectively at infinity. The lenses are assumed to be thin lenses. The paraxial approximation (small angles) is valid. Students often forget the negative sign, which is crucial as it signifies that the final image is inverted. Confusing the condition of 'normal adjustment' (image at infinity) with the condition for maximum magnification (image at near point D). Assuming the objective focal length should be small (like in a microscope), whereas in a telescope, f o is large.