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MotionLab
Where a lens actually forms an image — the formula behind cameras, telescopes, and eyeglasses.
This calculator uses a simplified version — real optics problems track positive/negative signs carefully to distinguish real images (light actually converges there) from virtual images (light only appears to come from there, like in a magnifying glass held close to an object).
When an object is placed closer to the lens than its focal length, the thin lens equation produces a negative image distance — physically, this means the lens can't form a real image and instead produces a virtual, magnified one, as with a magnifying glass.
Image distance (cm)
15
1/f = 1/dₒ + 1/dᵢ
What you entered
1/dᵢ = 1/f − 1/dₒ
1/10 − 1/30= 15 (image distance)Result
Image distance (cm): 15
A lens with focal length 10cm and an object at 30cm forms an image at 15cm.