L14: Telescopes

what can be used as low visions aids for near vision

magnifiers

calculation for linear magnification

image size/object size

name the 3 ways magnification is achieved

relative size magnification, relative distance magnification, and angular magnification

what is relative size magnification

increase the size of the object by non optical means

what is relative distance magnifcation

move the object closer to the eye

what is angular magnification

increase the visual angle subtended by the object at the eye by optical means

maximum magnification

magnifier positioned so the object lens eye sustem produces an image at the least distance of vision

formula for image formed at the least distance of vision

-q= (-l +d)

formula for nominal magnification

F/4

ormula for maximum magnification

1+F/4

how to increase field of view

1. keep distance between object and lens constant and move eye closer to lens

2. hold object inside the principal focus of magnifying lens

describe galilean telescope

+ve objective lens and -ve eyepiece seperated by sum of focal length

advntages of gailen telescope

1. produces upright image

   1. compact and lightweight

disadavntage of gailen telescope

1. low magnifcation

2. restricted field of view