Define the term Conjugate Foci.

Conjugate foci:

1. Focus is the point onto which collimated light parallel to the axis is focused.
2. Conjugate foci for a lens are defined as the set of points on the principal axis where the positions of the object and the image can be interchanged.
3. The conjugate foci can be described as the pair of two such points placed on the principal axis of any lens that, the object placed at the point, the image should be formed at a perfectly interchangeable point.
4.