1. The Optics of the Camera Obscura or
Why pinhole cameras are not cutting-edge

2. Electromagnetic
Radiation
Light
Photons

3. These three are the same…
Light
pure energy
Electromagnetic Waves
energy-carrying waves emitted by vibrating electrons
Photons
particles of light

6. EM Radiation Travels as a Wave
c = 3 x 108 m/s

7. The Visible Spectrum
Light waves extend in wavelength from about 400 to 700 nanometers.

8. Transparent Materials
Transparent - the term applied to materials through which light can pass in straight lines.

9. Opaque Materials
Opaque - the term applied to materials that absorb light.

10. Are clouds transparent or opaque to visible light?
Answer: opaque
Are clouds transparent or opaque to ultraviolet light?
Answer: almost transparent

11. Special Things About a Light Wave
• It does not need a medium through which to travel
• It travels with its highest velocity in a vacuum
• Its highest velocity is the speed of light, c,
equal to 300,000 km/sec
• The frequency (or wavelength) of the wave determines
whether we call it radio, infrared, visible, ultraviolet,
X-ray or gamma-ray.

12. Camera Obscura
"When images of illuminated objects ... penetrate through a small hole into a very dark room ... you will see [on the opposite wall] these objects in their proper form and color, reduced in size ... in a reversed position, owing to the intersection of the rays". Da Vinci
Slide credit: David Jacobs

13. Jetty at Margate England, 1898.
(Jack and Beverly Wilgus)
Slide credit: David Jacobs

14. Pinhole Cameras Pinhole camera - box with a small hole in it
Image is upside down, but not mirrored left-to-right
Question: Why does a mirror reverse left-to-right but not top-to-bottom?
The point to make here is that each point on the image plane sees light from only
one direction, the one that passes through the pinhole.

15. Pinhole and the Perspective Projection
Is an image being formed
on the screen?
YES! But, not a “clear” one.
(x,y)
screen
scene
image plane
effective focal length, f’
optical
axis y x z
pinhole

16. Magnification y z x d f’ optical axis Pinhole d’ planar sceneB d f’
optical
axis z A
Pinhole A’ d’ x
planar scene
image plane B’
From perspective projection:
Magnification:

17. Properties of Projection
Points project to points
Lines project to lines
Planes project to the whole or half image
Angles are not preserved
Degenerate cases
Line through focal point projects to a point.
Plane through focal point projects to line

18. Distant Objects are Smaller
Size is inversely proportional to distance.
Note that B’ and C’ labels should be switched.

19. Problems with Pinholes
Pinhole size (aperture) must be “very small” to obtain a clear image.
However, as pinhole size is made smaller, less light is received by image plane.
If pinhole is comparable to wavelength of incoming light, DIFFRACTION
effects blur the image!
Sharpest image is obtained when:
pinhole diameter
Example: If f’ = 50mm,
= 600nm (red),
d = 0.36mm

20. The Reason for Lenses