Spark image
Lens formula
Lens formula: 1/object distance(u) + 1/image distance(v) = 1/focal length(f)
1/u + 1/v = 1/f

This applies to all types of lens as long as the correct sign convention is used when substituting values for the distances. (Reminder: we use the ‘real is positive, virtual is negative’ sign convention here.)

n1/u + n1/v + = [n2 – n1][1/R1 + 1/R2 ] =n1/f

If n1 = 1 (i.e. the lens is in air) the formula becomes: 1/u + 1/v = 1/f

This formula could be used to calculate the refractive index (n2) of the glass of the lens.
 
 
 
© Keith Gibbs 2009