Thin Lens Focal Length Calculator
Calculate focal length, object distance, or image distance using the thin lens equation
About this calculator
The Thin Lens Focal Length Calculator uses the fundamental thin lens equation (1/f = 1/do + 1/di) to solve for any unknown variable when two values are provided. This tool is essential for physics students, optical engineers, and photographers working with lens systems. It helps determine focal length for lens identification, calculate object distances for proper positioning, or find image distances for screen placement and camera focusing applications.
How to use
Enter any two known values from focal length, object distance, and image distance into the calculator. The tool will automatically compute the missing third value using the thin lens equation. Use positive values for real distances and negative values for virtual images or diverging lenses according to sign conventions.
Frequently asked questions
What is the thin lens equation?
The thin lens equation is 1/f = 1/do + 1/di, where f is focal length, do is object distance, and di is image distance.
When do I use negative values?
Use negative focal length for diverging lenses, negative object distance for virtual objects, and negative image distance for virtual images.
What units should I use?
Use consistent units throughout (all in cm, mm, or meters). The calculator maintains the same units for all measurements entered.