What is the term for the geometric center of a lens?

The term "geometric center" refers to the exact midpoint of the lens, which serves as a crucial reference point in optics. Although this term is accurate and often used interchangeably with certain other terms, the most commonly accepted term for the specific point that is considered the geometric center of a lens in optics is the "optical center".

The optical center is defined as the point within a lens where light rays traveling parallel to the optical axis can pass through without being affected by refraction. This central point is critical for ensuring that the lens performs its intended function effectively, allowing for distortion-free vision and accurate prescription fulfillment.

The distinction between these terms often presents confusion. While the geometric center provides a basic spatial reference, the optical center is more vital when discussing the behavior of light through the lens — particularly in terms of alignment with the optical axis. Understanding this nuanced difference is key for both practical and theoretical applications in optics and lens design.