Chapter 5: Spherical Lenses Flashcards
Define the first principle focus
The first principal focus, F1, is the point of origin of rays which, after refraction by the lens, are parallel to the principal axis. The distance F1N is the first focal length f1.
Define the second principle focus.
Incident light parallel to the principal axis is converged to or diverged from the second principal focus, F2. The distance F2N is the second focal length, f2. By the sign convention (see p. 31) f2 has a positive sign for the convex lens, and a negative sign for the concave lens.
Lenses are designated a plus or minus sign based on which focal points, 1 or 2?
2
Therefore, for concave lenses, they are designated as minus lens
For convex lenses they are designated a plus.
What is the thin lens formula
1/v- 1/u = 1/f2
V = image distance from principle plane
U = object distance from principle plane
F2 = second focal length.
If you know 2 of the values, you can calculate the 3rd. Can also be used to work out magnification (v/u).
Describe image formed from a convex mirror when object is placed outside of principle focus.
Describe image formed by object at the principle focus of an convex lens
see image below
Describe image formed by object inside the principle focus of an convex mirror
Describe image formed by object outside the principle focus of an concave lens
The image formed by a thin concave lens is the same regardless of the position of the object relative to the focal point
How to draw ray diagram
1 line from top of an object through the nodal point undeviated
1 line from top of an object, deviated to F2
How do you calculate the diopteric power of a lense
1/ f2
So for convex lens it is positive
For concave lens it is negative
F2 is measured in cm
How to calculate linear magnification of spherical lens
How do you calculate the apparent size of an image?
This is why the moon looks to be the same size as a coin when held up infront of your eye
In angular magnification, what is unity?
How do you calculate the magnification of a lens
M= F/4
Where F = power in dioptres
What is prismatic decentration?
When light hits the periphery of a lense, it gets refracted more than ones at the centre. This is a cause of spherical aberration. This can cause jack in the box scotoma.
