Two lenses A and B have focal lengths of + 20 cm and, -10 cm, respectively. (a) What is the nature of lens A and lens B ? (b) What is the power of lens A and lens B ? (c) What is the power of combination if lenses A and B are held close together ?
a)- For converging lenses, the focal length is always positive, while diverging lenses always have negative focal lengths.
so A is converging and B is diverging lens.
b) Pa = 120=0.05D
Pb = 1−10=−0.1D