Human Eye Lens: Object at 25 cm (Near Point)
Modeling the human eye with a relaxed focal length of ~17 mm and an object at 25 cm helps illustrate near-point vision.
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.
The near point of a healthy young eye is about 25 cm; this preset illustrates the lens equation for that viewing distance.
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.