Concave Lens: −15 cm Focal Length, Object at 30 cm
A concave (diverging) lens with f = −15 cm and object at 30 cm produces a virtual image at −10 cm (same side as object).
How to use this tool
- Enter focal length f, object distance dₒ and image distance dᵢ in the fields above.
- Results update instantly as you type — or click Calculate.
- Read your image distance dᵢ and the full breakdown beneath it.
Concave lenses always produce virtual, upright, diminished images regardless of object position — this preset shows a typical case.
Frequently asked questions
- What is the sign convention?
- Using the standard convention: distances are positive on the same side as the outgoing light (real image), negative on the same side as the incoming light (virtual image). Converging lenses have f > 0; diverging lenses f < 0.
- What happens when the object is at the focal point?
- The image distance becomes infinite (parallel outgoing rays) — no focused image forms.