Knapp's law is applied primarily for axial ametropes and states that a lens placed at the primary focal point will produce a retinal size magnification of what value?

Knapp's law is applied primarily for axial ametropes and states that a lens placed at the primary focal point will produce a retinal size magnification of what value?

• A. 0
• B. 0.5
• C. 1
• D. 2

Answer: (C)

Knapp's law describes how retinal image size behaves for axial ametropes when a correcting lens is placed at the eye’s primary focal point. In this setup, the retinal magnification is unity, meaning the image on the retina has the same linear size as the object being viewed. This occurs because placing the lens at the primary focal point makes the eye's optics project a retinal image that preserves size, so there is no extra minification or magnification. Therefore the retinal size magnification is 1.

Knapp's law describes how retinal image size behaves for axial ametropes when a correcting lens is placed at the eye’s primary focal point. In this setup, the retinal magnification is unity, meaning the image on the retina has the same linear size as the object being viewed. This occurs because placing the lens at the primary focal point makes the eye's optics project a retinal image that preserves size, so there is no extra minification or magnification. Therefore the retinal size magnification is 1.