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Optical Lens Thickness Formula:
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The optical lens thickness calculation determines the total thickness of a lens considering both the base thickness and the additional thickness contributed by prism correction. This is important for proper lens fitting and cosmetic appearance.
The calculator uses the optical lens thickness formula:
Where:
Explanation: The formula accounts for both the base thickness required for the prescription and the additional thickness needed to create the prismatic effect.
Details: Accurate thickness calculation ensures proper lens fitting in frames, prevents edge defects, and helps predict the cosmetic appearance of the glasses. It's particularly important for high-power prescriptions and prism corrections.
Tips: Enter base thickness in mm, prism power in diopters, and the refractive index of the lens material. Common refractive indices are 1.5 (CR-39), 1.6 (polycarbonate), and 1.67 or 1.74 (high-index).
Q1: Why does prism increase lens thickness?
A: Prism is created by making one side of the lens thicker than the other. The amount of thickness needed depends on the prism power and material's refractive index.
Q2: What's a typical base thickness?
A: Standard plastic lenses typically have 1.0-2.0 mm base thickness, while high-index lenses may be thinner (0.7-1.5 mm).
Q3: How does refractive index affect thickness?
A: Higher refractive index materials require less thickness for the same prism power, allowing for thinner lenses.
Q4: What's the maximum prism that can be ground into a lens?
A: This depends on the lens size, material, and base curve. Typically 6-8Δ can be ground into most lenses without excessive thickness.
Q5: How is thickness distributed in a prism lens?
A: For base-out prism, thickness is added to the temporal side; base-in adds to the nasal side; base-up adds to the top; base-down adds to the bottom.