For sunglasses, not only the original lens quality needs to be high, but the way the lens is processed also affects the final frame quality.
That’s why the lens processing must be carefully checked.
1. Size and Fit Requirements
(1) Size Requirements
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The A and B measurements must match the drawing. The usual tolerance is ±0.2mm.
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Lens thickness must match the production order. The usual tolerance is +0.2mm / -0.1mm. Both lenses in one pair should be the same thickness, with a max difference of ±0.1mm.
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Lens curve tolerance: ±0.25D.
(2) Fit Requirements
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The lens curve must match the frame curve. Tolerance: ±0.25D.
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After cutting, the lens should fit into the frame with the right tightness—not too loose, not too tight.
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For nylon sunglasses, the U-groove must be in the center. The edges should not be too rough, and the lens should fit the frame just right.
2. Surface Appearance Inspection Standards
(1) Lens Area Division and Defect Limits for Finished Sunglass Lenses
① Area Division:
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Area A is a 30mm circle around the pupil center (based on PD = 64mm).
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Area B is a 10mm ring around Area A.
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All other parts are Area C. (See Figure 4-6 for the area diagram.)
② In Area A, only one small defect like a black dot, tear drop, or light leak is allowed, and it must be no larger than 0.1mm. No scratches, peeling, or color loss are allowed.
③ Area A and Area B cannot both have two or more types of defects at the same time.
④ The total number of defects in Area A and B on one side must not be more than 3.
⑤ Scratches, cracks, deformations, color fading, stains, mixed colors, pits, roughness, orange peel texture, waves, or strong marks are not allowed in Area A and B. The lens surface must be clean and smooth, with no dust, fibers, particles, stains, oil, or sweat.
(2) Unacceptable Standards
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The center area cannot have one clear scratch longer than 10mm.
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The non-center area cannot have three clear scratches longer than 10mm.
(3) Acceptable Standards
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The center area can have one faint scratch shorter than 10mm.
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The non-center area can have up to three faint scratches shorter than 10mm, but they should not all be in one spot.