Increasing diameter results in a ____ focus.

Increasing diameter results in a ____ focus.

• A. Shallower
• B. Wider beam
• C. Deeper
• D. Same

Answer: (C)

Increasing the diameter of the focusing element boosts the system’s numerical aperture, allowing the rays to converge more tightly and with less diffraction spread. This tighter convergence means the energy remains concentrated over a longer distance along the optical axis, so the focal region extends deeper into the medium. In other words, a larger diameter makes the focus reach deeper rather than shallower or staying the same. The other options describe shallower focus, a change in beam width at the focus, or no change at all, which don’t align with how a bigger aperture alters focus depth.

Increasing the diameter of the focusing element boosts the system’s numerical aperture, allowing the rays to converge more tightly and with less diffraction spread. This tighter convergence means the energy remains concentrated over a longer distance along the optical axis, so the focal region extends deeper into the medium. In other words, a larger diameter makes the focus reach deeper rather than shallower or staying the same. The other options describe shallower focus, a change in beam width at the focus, or no change at all, which don’t align with how a bigger aperture alters focus depth.