1. Fundamental of Optical Engineering Lecture 3

2.  Aberration happens when the rays do not converge to a point where it should be. We may distinguish the aberrations into 6 categories: ◦ Spherical aberration ◦ Coma ◦ Oblique astigmatism ◦ Curvature of field ◦ Distortion ◦ Chromatic aberration

3.  Rays near axis come to focus at a different distance than marginal rays.  In other words, rays that pass through a lens further away from the optical axis come to a focus closer to the lens than paraxial rays.

5.  This spherical aberration can not be completely corrected with a simple lens.  Complete elimination of this aberration can be done by using a compound lens.

6.  This happens due to various wavelengths in light rays.  The index of refraction varies as a function of wavelength.  A single lens has different focal lengths for different colors.

7.  Chromatic aberration can be corrected by using two lenses in contact, one made of crown and the other of flint.

8.  A plane mirror reflects the light without focusing it.  The virtual image formed by a plane mirror is located at the same distance behind the mirror as the object is in front of it.

10.  Assume θ << 1

11.  For h = 10 cm., R = 2m. Find f.

12.  Incident beam travels left to right, reflected light travels right to left.  Distance is measured from plane of mirror.  Object is on the left of a mirror, then object distance s < 0.  Image to the left of a mirror, then object distance s’>0 (virtual image). Image to the right of a mirror, then image distance s’< 0 (real image).

13.  For converging mirror, focal length f > 0.  For diverging mirror, focal length f < 0.

16.  Think of the last time you viewed yourself in a mirror. (a)Assuming that the mirror surface is perfectly flat, what are its radius of curvature and its focal length? (b)Is the image formed by the mirror real or virtual?

17.  The simplest type of camera is the pinhole camera.  The sharpness of the image depends on the diameter of the hole.  If it is too large, the image is blurred.  Thus, as the pinhole is small, the image improves in clarity until a certain pinhole size.

18.  The advantage of a pinhole camera apart from its simplicity is that all objects are in focus on the screen.  The depth of field of the camera is unlimited.  The disadvantage of pinhole camera is that it admits limited light, so that it is not suitable in freezing the action of moving objects.  Some put a converging lens to improve the brightness and sharpness of the image.

19.  The aperture, which admits light to the film, is variable and coordinated with the exposure time (shutter speed).  The light power incident at the image plane is expressed as

20.  A lens of f = 4 cm is stopped down to an aperture of 0.5 cm (D). What is the relative aperture or f-number?

21.  From the figure above, the depth of field is (s 2 – s 1 ) that may be expressed as

22.  We clearly see that although the interval is symmetric about s 0 ’ in image space, the depth of field interval is not symmetric about s 0. Large DSmall D More light collected. (slower film, fast action) Better depth of field. Better spatial resolution

23. Source: Wikipedia

24.  There are 3 well-known defects in vision due to errors of refraction of the eyes. ◦ Near-sightedness (Myopia): Longer distance from cornea to retina than usual. ◦ Far-sightedness (Hyperopia): Shorter distance from cornea to retina than normal. ◦ Astigmatism: Unequal (asymmetric curvatures) in the corneal surface.

25. Note: The distance for best viewing for adult is 25 cm.

26.  GTLE:

27.  A near-sighted person has a far point of 100 cm and a near point of 15 cm. (a)What f of the lens should be to move the far point to infinity? (b)With this correction lens, can this person read a book at the normal near point (25 cm from the eye)?

28.  The magnifying glass is used for better spatial resolution in image.  On the other words, it helps us to see smaller objects or to be able to distinguish finer features.

30.  What does “20x lens” mean?

31.  The magnification of small objects is achieved by the use of two postitive lenses: objective lens and an eyepiece.

32.  The magnification is approximated by  The standard tube length is 16 cm.  By viewing with the microscope, the image formation may be drawn as