In a plus lens where would the optical center be located?

• A. At the apex
• B. At the center of the lens
• C. At the edge
• D. Where both bases meet

Answer: (D)

The main idea is that the optical center is the point in a lens where a light ray passing through along the axis goes straight through without bending. For a plus (converging) lens, this point sits at the middle of the lens along the optical axis—the spot where the two curved surfaces’ central regions align in a cross‑section, effectively where the two bases meet. This is the location that governs undeviated passage of rays coming parallel to the axis, which is why it’s described as the point where the lens’s two bases meet. The apex or edge aren’t where a central ray passes untouched, so they aren’t the optical center. The center of the lens is close to the actual optical center in simple diagrams, but the defining idea is that the undeviated passage occurs at that central meeting point.