Why do the surfaces of polished lenses sometimes exhibit “sand holes” or “pitted spots”?-Shanghai Xuanfeng Optoelectronic Technology Co., Ltd.

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Why do the surfaces of polished lenses sometimes exhibit “sand holes” or “pitted spots”?

2026-08-25

“Scratches” typically arise when the damaged layer left by the preceding process—whether rough grinding or fine grinding—is not completely removed. Possible causes include: ① The abrasive grains used in the previous step were too coarse, resulting in an excessively deep damage layer. ② Insufficient polishing time or improper selection of the polishing‑powder particle size. We rigorously control the material removal at each stage of the process to ensure that fine grinding can fully eliminate the scratches from the prior step and that adequate polishing allowance remains.

“Sand holes” typically arise when the damaged layer left by preceding processes—such as rough grinding or fine grinding—is not completely removed. Possible causes include:
① The grit size of the preceding process is too coarse, resulting in excessive damage to the surface layer.
② Insufficient polishing time or improper selection of polishing powder particle size.
We rigorously control the amount of material removed at each machining step to ensure that fine grinding completely eliminates any scratches from the previous operation, while leaving sufficient stock for polishing.

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