Vergence and focal length Flashcards
(20 cards)
What is the significance of curvature in focusing calculations?
Curvature of the light wavefronts that hit and leave the surface/lens is important for calculations.
What is the formula for object vergence?
L = n/ℓ
Where L is the object vergence, n is the refractive index of the object medium, and ℓ is the object distance.
How is the power of a single optical surface calculated?
F_surf = (n’ – n)/r_surf
Where n’ is the refractive index of the image medium and r_surf is the radius of curvature of the optical surface.
What is the relationship between L, F_surf, and L’?
L’ = L + F_surf
L’ is the curvature of light wavefront that leaves the surface.
How do you find the image distance ℓ’ from L’?
ℓ’ = n’/L’
Where L’ is the curvature of light wavefront leaving the surface.
What is the first focal length?
The first focal length is the special object distance where light from an object will image at optical infinity.
What is the second focal length?
The second focal length is the special image distance where light from an object at optical infinity will form an image.
How are f and f’ related to the optical surface?
f and f’ are constants for a given surface.
What is the formula for the first focal length f?
f = n/-F_surf
Where F_surf is the power of the surface.
Calculate f given F_surf = +7.50D and n = 1.
f = 1/-(+7.50) = -0.133m
What is the formula for the second focal length f’?
f’ = n’/F_surf
Where F_surf is the power of the surface.
Calculate f’ given F_surf = +7.50D and n’ = 1.6.
f’ = 1.6/+7.50 = +0.213m
True or False: The first and second focal lengths are equal.
False
What sign convention applies to the first and second focal lengths?
One focal length is positive and the other is negative.
What determines the sign of the second focal length?
The second focal length has the same sign as the power of the surface.
What type of object distance is used to calculate the first focal length?
A real object in air.
Fill in the blank: The radius of curvature is denoted as _______.
r_surf
What refractive index is used for glass in the example problem?
n_glass = 1.7
What refractive index is used for plastic in the example problem?
n_plas = 1.5
What is the radius of curvature used for the concave surface example?
15mm
