Focal Length Calculator
Calculate the focal length of a lens using object and image distances
About this calculator
The Focal Length Calculator determines the focal length of a lens using the thin lens equation, which relates object distance, image distance, and focal length. This tool is essential for photographers, opticians, and physics students who need to understand lens behavior and calculate optical properties. By inputting the distances between the lens and object, and lens and image, you can quickly determine the focal length, which is crucial for camera lens selection, microscope design, and optical system optimization.
How to use
Enter the object distance (distance from lens to object) and image distance (distance from lens to formed image) in the input fields. The calculator will automatically apply the thin lens equation (1/f = 1/do + 1/di) to compute the focal length. Results are displayed instantly as you input values.
Frequently asked questions
What is focal length in photography?
Focal length is the distance between the lens and image sensor when focused at infinity, determining field of view and magnification characteristics of the lens.
How does object distance affect focal length calculation?
Object distance is measured from the lens center to the subject. Closer objects require different image distances to maintain focus, affecting the calculated focal length.
Can this calculator work for both converging and diverging lenses?
Yes, the calculator works for both lens types. Converging lenses produce positive focal lengths, while diverging lenses produce negative focal lengths in the results.