Certified Paraoptometric (CPO) Practice Exam 2025

What type of lens converges parallel light?

1. Convex, Plus

2. Concave, Minus

3. Single vision

4. Multifocal

The correct answer is: Convex, Plus

The correct choice is a lens that is convex, also referred to as a plus lens. Convex lenses are designed to converge (focus) parallel rays of light toward a single focal point. This property allows them to magnify images when used in various optical devices, including magnifying glasses, cameras, and corrective eyewear for hyperopia (farsightedness). Convex lenses are thicker in the center than at the edges, which gives them the ability to bend light rays that are entering the lens parallel to its axis, bringing these rays together. This fundamental characteristic makes convex lenses essential for applications where enhancing the focus of light is necessary. In contrast, a concave (minus) lens diverges parallel light rays away from a focal point, which is utilized primarily in devices intended for myopia (nearsightedness). Single vision and multifocal lenses refer to types of prescriptions rather than the physical properties of the lenses themselves, so they do not specifically address the question about how they handle parallel light.