Last updated on June 15th, 2023 at 04:55 pm
Lens Formula – A formula that gives the relationship between image distance (v), object distance (u), and focal length (f ) of a lens is known as the lens formula. This lens formula applies to both types of spherical lenses: convex lenses as well as concave lenses.
Lens Formula | spherical Lens equation
The lens formula can be written as :
1/v – 1/u = 1/f
where v = image distance,
u = object distance,
and f = focal length.
See solved Lens numerical problems here.
Read: sign convention for Lens
Difference between the Lens formula and the Mirror formula
Please note that the lens formula differs from the mirror formula only in the sign between
1/v and 1/u .
The mirror formula is 1/v + 1/u = 1/f whereas the lens formula is 1/v – 1/u = 1/f.
It is clear that the mirror formula has a plus sign (+) between 1/v and 1/u whereas the lens formula has a minus sign (–) between 1/v and 1/u.
The values of v and u should be substituted in the lens formula with their proper signs.