EVERYDAY CLARITY
Focal Length Calculator
What focal length follows from object and image distance? Enter the stated values to calculate this model.
Your result
Focal length
m
Result for the values shown.
Calculations run in your browser.
What to enter
| Input | Meaning and units |
|---|---|
| Signed object distance (m) | Enter signed object distance in m; use the same basis as the other measurements. |
| Signed image distance (m) | Enter signed image distance in m; use the same basis as the other measurements. |
Understanding your result
Read Focal length (m) in the units and model stated on this page. The formula f=object*image/(object+image) defines the relationship; measurement accuracy and model applicability are separate from numerical precision.
Common mistakes
- Mixing input units or changing the physical meaning of a variable without changing the model.
Check your calculation
- Use the worked example as a known reference case, then change one input at a time and check the direction and units of the response.
Calculation checks, sources and review limits
What focal length follows from object and image distance?
What focal length follows from object and image distance? Enter the stated values to calculate this model.
Common uses
- What focal length follows from object and image distance
How it works
f=object*image/(object+image)
Worked example
Enter Signed object distance: 0.3 m; Signed image distance: 0.15 m. Results: Focal length: 0.1 m.