OP - Introduction to Wavefront Aberrometry & Image Quality Metrics 1 - Week 4

Question 1

Define vergence of a wavefront.

Answer 1

It is equal to the inverse of the distance from the wavefront to its origin, apparent origin, or destination.
Units in D.

Question 2

Define vergence of an object.

Answer 2

When an object is placed in front of an observer, it has a vergence that is equal to 1/distance to the eye.

Question 3

Relate refractive error and vergence.

Answer 3

Your refractive error is -1x the vergence of the wavefront that emerges from a point source on your retina.

Question 4

Define Fraunhofer/far-field diffraction, and give examples of what it looks like.

Answer 4

When collimated light passes through an aperture, the light distribution doesnt take the shape of the aperture, but because it self-interferes a diffraction pattern occurs.
Airy disks are one example.

Question 5

Define the strehl ratio.
What is the strehl ratio of a normal-sized pupil that has been corrected for defocus/astigmatism?
What about for a 1mm pupil? What is the image quality like?

Answer 5

It is a measure of the quality of the image formation.
A perfect unaberrated system has a value of 1.
For a 5mm pupil it is 5%
For a 1mm pupil, it is close to 1, but the image quality is poor due to refraction.