Lens Magnification Calculator
Enter any two of focal length, object distance and image distance to solve the thin lens equation. The calculator finds the third value and the magnification.
How to use the lens magnification calculator
- Enter any two of focal length, object distance and image distance in cm.
- Leave the value you want to solve for blank.
- Read the solved distance and the magnification.
Examples
Object beyond the focal point
f = 10 cm, object = 15 cm
image = 30 cm, magnification = -2
Object inside the focal point
f = 10 cm, object = 5 cm
image = -10 cm (virtual), magnification = 2
Frequently asked questions
What is the thin lens equation?
It relates focal length and distances as 1/f = 1/do + 1/di, where do is the object distance, di is the image distance and f is the focal length.
How is magnification calculated?
Linear magnification is m = -di / do. A negative value means an inverted real image; a positive value means an upright virtual image.
What does a negative image distance mean?
A negative image distance marks a virtual image on the same side as the object, as when an object sits inside the focal length of a converging lens.
What sign convention does this use?
Distances in front of the lens and converging focal lengths are positive. Virtual images give a negative image distance and a positive magnification.
Why does an object at the focal point fail?
When the object distance equals the focal length, the rays leave parallel and the image forms at infinity, so no finite image distance exists.
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