OP - Image Formation and Ray Tracing - Week 3

Question 1

What is the minimum number of rays that need to be traced to determine the image position, not including the optical axis?

Answer 1

2.

Question 2

How are virtual images formed? Describe how they can be identified in terms of projection screen placement.

Answer 2

Consider an optical system that diverges a beam.
If the diverging beams are ray-traced, they will converge at a point different to the object location., and thus appear to be closer or further away.
A projection screen cannot be placed on the image plane to form an image.

Question 3

What is a beam that is neither convergent nor divergent considered to be?

Answer 3

Neither real nor virtual.

Or can be considered an image at infinity.

Question 4

Describe the sign conventions with the optical axis as the focus.

Answer 4

Distances above or to the right of the optical axis are positive.
Below and to the left are negative.

Question 5

When are angles positive/negative?

Answer 5

Counterclockwise to the normal - positive

Clockwise to the normal - negative

Question 6

Describe the steps of ray-tracing.

Answer 6

Use the sine rule to find the angle i
Calculate i' using snells law
Calculate angle g
calculate angle u'
Find distance l'
Find l for the next surface
Back to step 1 if another surface exists

Question 7

What are aberrations? How does paraxial optics fit into this? How does this explain the mechanisms of increased visual acuity from pinholes?

Answer 7

Lenses do not focus onto a single convergent point, instead are spread out.
Close to the optical axis however, the the rays do converge very well onto a single point - paraxial optics.
Hence why pinholes increase visual acuity, by blocking aberrations.