Two-Lens System (Combined Focal) calculator
Combined focal length and BFL of two thin lenses separated by d.
Category: Geometric Optics
Formula: 1/F = 1/f₁ + 1/f₂ − d/(f₁·f₂)
Inputs
| Input | Parameter | Unit | Default |
|---|---|---|---|
| f₁ | f1 | mm | 50 |
| f₂ | f2 | mm | 100 |
| Separation d | d | mm | 20 |
Result with the default inputs
- Combined F: 38.4615 mm
- Back focal len: 23.0769 mm
Open it with your own values: put each input in the address as a parameter, for example /calculators/two-lens-system-combined-focal?f1=50. A unit other than the listed one goes in <parameter>_unit.
Read more: Wikipedia: Lens, Compound lenses