The front curve and thickness of the lens will affect both magnification of images
seen through the lens as well as the size of images
reflected off the front surface of the lens.
For a given power, as either the center thickness or front curve of the lens increases, magnification through the lens increases, and vice versa.
The relative amount of spectacle magnification
M due to the front curve and center thickness of the lens is given approximately by:
where
F1 is the front curve,
t is the center thickness in centimeters, and
n is the refractive index.
The convex front surface of the lens also acts like a convex mirror, which will make
reflected images appear smaller.
Flattening the front curve will increase the size of reflected images, although this should not trouble the wearer as much as changes in the magnification of images seen through the lens.
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