Chapter 25

Optical Instruments1. The eye2. The magnifying glass

The Eye - Parts

Cornea Aqueous Humor – The pupil The crystalline

lens The iris

The Eye – Operation

The cornea-lens system Rods and Cones Accommodation

The Eye – Focusing The eye can focus on a distant

object The eye can focus on near objects The near point The far point

Farsightedness

Nearsightedness

Presbyopia, Astigmatism and Diopters Presbyopia Astigmatism Diopters

Example What focal length must a

corrective lens have to enable the eye to see clearly an object 25.0 cm away if the near point is 50 cm away? What is the power of this lens?

Example A particular nearsighted person

cannot see objects clearly when they are beyond 25 cm (the far point of the eye). What focal length should the prescribed lens have to correct this problem? What is the power of this lens?

Simple Magnifier What is it? How does it work? What is angular

magnification? How do I calculate it? What is the near

point of the eye? Single and Multiple

lens

Example - Simple Magnifier

1. A magnifying glass has a focal length of 15cm. If the near point of the eye is 25 cm from the eye , what is the angular magnification of the glass.

Compound Microscope

A compound microscope consists of two lenses

Gives greater magnification than a single lens

The objective lens has a short focal length, ƒo<1 cm

The ocular lens (eyepiece) has a focal length, ƒe, of a few cm

The Camera The single-lens

photographic camera is an optical instrument

Components Light-tight box Converging lens

Produces a real image

Film behind the lens Receives the image