1. SPHERICAL MIRROR EQUATIONS
AND SIGN CONVENTION
Concave Mirror Illustrated
Light In Side
do > 0 Real Object
do < 0 Virtual Object F V
Optic Axis C
Light Out Side
di > 0 Real Image
C This Side, R > 0
di < 0 Virtual Image
C This Side, R < 0
Definitions: C – Center of Curvature
R – Radius of Curvature
F – Focal Point (Same Side as C)
V – Vertex
Equations: Paraxial Approximation

2. THIN LENS EQUATIONS AND SIGN CONVENTION Surface 1 Surface 2
Light In Side
do > 0 Real Object
di < 0 Virtual Image
C1 This Side, R1 < 0
C2 This Side, R2 < 0
Light Out Side
do < 0 Virtual Object
di > 0 Real Image
C1 This Side, R1 > 0
C2 This Side, R2 > 0
– Index of Refraction
When in Air
Definitions: C1 – Center of Curvature, Surface 1
C2 – Center of Curvature, Surface 2
Illustrated Lens is Double Convex Converging
With C1 on the Light Out Side and C2 on the Light In Side
Equations:

3. REFRACTION AT SPHERICAL INTERFACE BETWEEN TWO OPTICAL MATERIALS
Light In Side
do > 0 Real Object
di < 0 Virtual Image
C This Side, R < 0
na – Index of
Refraction
Light Out Side
do < 0 Virtual Object
di > 0 Real Image
C This Side, R > 0
nb – Index of
Refraction
Illustrated Interface Has C, Center of Curvature,
On The Light Out Side, Thus R > 0
A Flat Interface Has R = ∞