L5 Thin Lenses

Question 1

What are the two categories of lenses

Answer 1

1. Convex (converging, +ve) - equi, Plano, bi, converging meniscus
2. Concave (diverging, -ve) - equi, Plano, bi, diverging meniscus

Question 2

What is a thin lens (4 deciding factors)

Answer 2

1. Central thickness considered small enough that it doesn’t affect the power
2. In ray tracing, thin lenses are drawn as a straight line (plane) normal to the optical axis
3. Refraction takes place at this plane
4. has two refracting surfaces (front&back)

Question 3

Define optical axis

Answer 3

Line that passes though two radii of curvature of the two refractive surfaces (front&back)

Question 4

Define vertex

Answer 4

Point(s) where lens surfaces and optical axis intersect

Question 5

Explain concept of bending a lens

Answer 5

Changing the RADII of the two refracting surfaces whilst keeping the TOTAL surface power SAME

Question 6

how to calculate thin lens power

Answer 6

F=(n’-n)(1/r1-1/r2)

where n’ is the lens index, n index in air

Question 7

explain object and image positions for lenses

Answer 7

• object space on left on lens, object within is real, image within is virtual
• image space on right of lens, image within is real, object within is virtual

Question 8

Prismatic effect on +ve thin lens

Answer 8

Base-to-base, will displace the image opposite of decentration

Question 9

Prismatic effect of -ve lens

Answer 9

Apex-to-apex, will displace the image in the same direction of decentration

Question 10

How to calculate decentration (magnitude of the prismatic deviation)

Answer 10

Multiply the displacement (cm) by the lens power (D)