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Design Realization lecture 25
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Retro-reflector gain

Retro-reflector gain

The retro-reflection response of a screen is normally rated in terms of gain.

Gain = ratio of peak reflected light energy to the energy reflected by a Lambertian surface.

Gains may be 1000 or more.

Light source only needs 1/1000 of the light energy to illuminate the screen, as long as the viewer is close enough to the source.

Slide 22

Application: personal displays

Application: personal displays

Each user has a personal projector (e.g. a PDA with a single lens in front of it), and projects on the same retro-reflective screen.

Slide 23

Application: Artificial backgrounds

Application: Artificial backgrounds

Projector and camera along same optical axis, project scene onto actors and retro-reflective background.

Cameras sees background only on screen, not on the actors (3M received technical academy award for this in 1985).

Slide 24

Convex Lenses

Convex Lenses

A refractive disk with one or two convex spherical surfaces converges parallel light rays almost to a point.

The distance to this point is the focal length of the lens.

Slide 25

Lenses

Lenses

If light comes from a point source that is further away than the focal length, it will focus to another point on the other side.

Slide 26

Lenses

Lenses

When there are two focal points f1 , f2 (sometimes called conjugates), then they satisfy:

Slide 27

Spherical Lenses

Spherical Lenses

If the lens consists of spherical surfaces with radii r1 and r2, then the focal length satisfies 1/f = ( - 1) (1/r1 - 1/r2)

Slide 28

Spherical aberration

Spherical aberration

Spherical lenses cannot achieve perfect focus, and always have some aberration:

Slide 29

Spherical aberration

Spherical aberration

Compound lenses, comprising convex, concave or hybrid elements, are used to minimize aberration.

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