APERTURE D = F/f where d is the aperture of the objective F is the focal length of the objective f is the f-number (f/) of the objective MAGNIFICATION: BY FIELDS M = Alpha/Theta where M is the magnification Alpha is the apparent field Theta is the true field Apparent Field: the closest separation eye can see is 4', more practically 8-25', 1-2' for good eyes. The Zeta Ursae Majoris double (Mizar/Alcor) is 11.75'; Epsilon Lyrae is 3'. True Field (in ?) = 0.25 * time * cos of the declination (in ') = 15 * time * cos of the declination where time is the time to cross the ocular field in minutes A star therefore moves westward at the following rates: 15? /h (1.25?/5 min) at 0? declination 13? /h (1.08?/5 min) at 30? declination 7.5?/h (0.63?/5 min) at 60? declination. MAGNIFICATION: BY FOCAL LENGTHS M = F/f where M is the magnification F is the focal length of the objective f is the focal length of the ocular At prime focus (ground glass), magnification is 1x for each 25 mm of F MAGNIFICATION: BY DIAMETER AND EXIT PUPIL M = D/d where M is the magnification D is the diameter of the objective d is the exit pupil (5-6 mm is best; 7 mm may not produce a sharp outer image)
28) When an astronomical telescope is focused on a distant star, the distance of the eye piece from the objective is 60 cm. When focused on a distant flag post the eye piece must be drawn at 0.1cm. If the focal length of the eye piece is 5cm; what will be the distance of the pole from the objective? Assume that the eye is focused for infinity?
Answer is:
300 m
Explanation:
Related Optics MCQ with Answers
Answer is:
3 cm
Explanation:
Magnification produced by a lens m is given by v/u
Answer is:
in doing so, the focal length of the eye lens is effectively decreased
Explanation:
A far-sighted man who has lost his spectacles reads a book by looking through a small hole in the sheet of paper. Then in doing so, the focal length of the eye lens is effectively decreased
Answer is:
? = 2 R
Explanation:
A plano-convex lens is made of glass of refractive index 1.5.The focal length ? of the lens and radius of curvature R of its curved face are related as f = 2R
Answer is:
41397
Explanation:
The diopter is the unit of measure for the refractive?power?of a?lens. The?power?of alens?is defined as the reciprocal of its focal length in meters, or D = 1/f, where D is the?power?in diopters and f is the focal length in meters.?Lens?surface?power?can be found with the index of refraction and radius of curvature.