Shape factor x Power factor calculates the ___________________ for a thick lens.

• A. Spectacle magnification
• B. Prismatic magnification
• C. Image magnification
• D. Optical magnification

Answer: (A)

Spectacle magnification is determined by how a thick lens alters the size of the image you see, not just how strong the lens is. The lens’s shape and thickness affect how light rays are bent inside the lens, changing the lateral size of the image you would see if the lens were absent. This is the shape factor. At the same time, the lens’s overall optical power determines how much angular magnification the eye perceives. For thick lenses, the net magnification is essentially the product of these two influences—the shape factor and the power factor—giving the final spectacle magnification. Prismatic magnification comes from prism effects due to decentration or tilt, not from the combined shape and power effects that define spectacle magnification, and terms like image magnification or optical magnification are not the standard descriptors used for this specific thick-lens behavior.