Ophthalmic Optics Flashcards
7 cards from real ABO NOCE Basic Opticianry practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Ophthalmic Optics flashcards as text
What is the focal length of a +2.50 D lens?
Answer: 40 cm
Focal length (in meters) = 1 / power, so 1 / 2.50 = 0.40 m = 40 cm.
Chromatic aberration in lenses is caused by:
Answer: Different wavelengths of light being refracted at different angles
Different wavelengths (colors) of light have different refractive indices in a material, causing them to focus at slightly different points — this is chromatic aberration.
Which lens form has the least peripheral distortion for most prescriptions?
Answer: Best form (corrected curve)
Best form (corrected curve or best-form) lenses are designed with specific base curves that minimize oblique astigmatism and peripheral distortion.
The critical angle for total internal reflection depends on:
Answer: The refractive indices of both media at the interface
The critical angle is determined by sin(θc) = n2/n1, so it depends on the refractive indices of both the dense and less-dense media at the interface.
Oblique astigmatism in ophthalmic lenses is an example of which type of lens aberration?
Answer: Monochromatic (Seidel) aberration
Oblique astigmatism is one of the five classic Seidel (monochromatic) aberrations that affect the quality of images formed by lenses.
A high Abbe value (V-number) in a lens material indicates:
Answer: Less chromatic aberration
A high Abbe value means the material disperses different wavelengths of light less, resulting in less chromatic aberration and better optical clarity.
What happens to the optical path of light when it passes through the optical center of a lens?
Answer: It passes through without deviation
Light passing through the optical center of a lens is not deviated (no prismatic effect), regardless of lens power.