^Combination of lenses
Two or more lenses are combined to
- Increase magnification.
- Make final image erect.
- Reduce certain aberrations.
If two thin lenses of focal lengths f1 and f2 are separated by a distance d then the effective focal length and power of the combination is given by:
2. P = P1 + P2 – d P1 P2
3. m = m1 x m2 x m3 x – – – – – – – – –
Let us prove the above relations.
* A Zoom lens is based on this result such that f can be varied 0 to ∞ by changing d.