In the minimum blank size equation M = ED + 2d + 2mm, which term represents decentration per lens?

Study for the NBEO Physiological Optics Test. Prepare with flashcards and multiple-choice questions, each question has hints and explanations. Ace your exam!

Multiple Choice

In the minimum blank size equation M = ED + 2d + 2mm, which term represents decentration per lens?

Explanation:
In this minimum blank size equation, you’re figuring out how big a blank is needed to manufacture the lens with proper margins. The term that represents decentration per lens is the variable that sits in the 2d part of the formula. The ED term stands for the effective diameter of the lens, which sets the central size you must accommodate. The 2d accounts for decentration on both lenses (or both surfaces) by adding twice the offset, and the 2mm is a fixed edging/clearance margin. So the decentration per lens is represented by d. For example, if ED is 50 mm and decentration per lens is 1 mm, M would be 50 + 2(1) + 2 = 54 mm.

In this minimum blank size equation, you’re figuring out how big a blank is needed to manufacture the lens with proper margins. The term that represents decentration per lens is the variable that sits in the 2d part of the formula. The ED term stands for the effective diameter of the lens, which sets the central size you must accommodate. The 2d accounts for decentration on both lenses (or both surfaces) by adding twice the offset, and the 2mm is a fixed edging/clearance margin. So the decentration per lens is represented by d. For example, if ED is 50 mm and decentration per lens is 1 mm, M would be 50 + 2(1) + 2 = 54 mm.

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