How to use the two thin lenses equivalent focal length calculator
Find the combined focal length of two thin lenses separated by a distance. Enter first lens focal length, second lens focal length, separation between lenses in the fields above; the equivalent focal length is computed instantly and plotted on the chart so you can see how the answer changes.
Common searches this calculator answers include “two lens system focal length”, “combined lens focal length”, “lens separation”, “calculate two thin lenses equivalent focal length”, “find equivalent focal length”.
Formula
Variables
- f1 — First lens focal length (cm)
- f2 — Second lens focal length (cm)
- d — Separation between lenses (cm)
Worked example
With first lens focal length = 10 cm, second lens focal length = -20 cm, separation between lenses = 5 cm, the calculator gives equivalent focal length ≈ 13.33333 cm.
Frequently asked questions
What is the two thin lenses equivalent focal length calculator used for?
Find the combined focal length of two thin lenses separated by a distance. It helps with questions such as “two lens system focal length”, “combined lens focal length”, “lens separation”.
What is the formula for the two thin lenses equivalent focal length calculation?
Equivalent focal length (cm) = 1 / (1 / f1+1 / f2-d / (f1 × f2)). Here f1 is first lens focal length (cm), f2 is second lens focal length (cm), d is separation between lenses (cm).
What inputs do I need for the two thin lenses equivalent focal length calculator?
You need first lens focal length in cm, second lens focal length in cm, separation between lenses in cm. Each field is pre-filled with a typical example so you can see how the result responds as you edit the numbers.
How do I use the two thin lenses equivalent focal length calculator?
Type values into the input fields. Results and the chart update instantly. Use Reset to restore the example values, Copy results to paste them elsewhere, or Share to copy a link that preserves your inputs.
Is the two thin lenses equivalent focal length result exact?
Calculations use standard formulas and double-precision arithmetic, then display about seven significant figures. Real-world measurements carry uncertainty, so treat results as estimates unless your inputs are exact.