Which statement about lens blank thickness is true?

• A. The blank size has no effect on final thickness
• B. A larger plus lens blank will leave the final lens thicker
• C. A smaller plus lens blank will result in a thinner final lens
• D. A smaller plus lens blank reduces weight

Answer: (C)

In lens making, the starting thickness of the blank sets the maximum thickness the finished lens can have. For a plus lens, which needs more material at the center to achieve its positive power, the center thickness is particularly constrained by how thick the blank is to begin with. If you start with a smaller blank, there isn’t enough material left to reach as thick a center, so the final lens ends up thinner overall. This is why a smaller plus lens blank tends to produce a thinner final lens.

Blank size certainly matters for final thickness; it’s not accurate to say it has no effect. A larger blank can accommodate more material at the center, potentially yielding a thicker lens, though other design and safety constraints can influence the actual outcome. A smaller blank may also reduce weight, but the central point here is how the starting thickness limits the final thickness.