camera no lens inverted, real image film or screen

Camera

No lens

Inverted, real image

Film or screen

Camera

Camera

Distance between the lens and the film can be adjusted.

Camera lenses usually have more than one element.

Control the amount of light that reaches the film:

(a)Adjust the amount of time the shutter stays open (referred to as the shutter speed)

(b) Change the aperture diameter D.

Shutter and Aperture

f - numberf - number = Focal length / Aperture diameter = f / D

Larger f – number

Smaller aperture Less intensity (Intensity ~ D2 )

SLR Camera

1 – Lens elements 5 – Focusing screen 2 - Reflex mirror at 45-degree angle 6 - Condenser lens 3 - Focal plane shutter 7 - Pentaprism 4 - 35 mm film or sensor 8 - Eyepiece

Digital CameraInstead of film : An array of photocells on a semiconductor chip CCD (charge-coupled device)

Slide Projector

Inverted, real image

Digital Projectors: LCD array instead of slide.

The Eye

n = 1.437

Normal eye: Far point: ∞ Near point: Depends on age

Defects of Vision

Nearsightedness (Myopia):A person can clearly see objects that are near, but objects that are far appear blurred.Far point is less than infinity.

Caused by a refractive problem of the cornea or lens, or the eyeball is too long.

The corrective divergent lens forms a virtual image inside the eye’s far point .

Farsightedness (Hyperopia):A person can clearly see objects that are far away, but objects that are near appear blurred. Near point is farther than near point of the normal eye.

Caused by malfunction in the cornea or lens, or the eyeball is too short.

The corrective convergent lens forms a virtual image at or beyond the eye’s near point.

Defects of Vision

Astigmatism:The cornea is unevenly shaped, and bends and scatters light in different directions, which causes objects to look distorted and appear blurry.

Refractive Power = 1/f (meters) diopter