What are the small projections at the edge of a used Nikon 70-200mm lens element?

Asked 8/29/2026

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I inspected a used Nikon AF-S NIKKOR 70-200mm f/2.8E FL ED VR and noticed several small projections or irregular shapes at the edge of one internal element. They resemble cement separation, but not like the examples I’ve seen, and they don’t have the fibrous look of fungus. What is this likely to be, and is it likely to affect image quality?

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Originally by John. Source · Licensed CC BY-SA 4.0

John

11d ago

2 Answers

Some lens elements are air-spaced via a separator from its neighboring element. Some are in direct contacted with its neighbor. It is common that a clear cement is applied when elements are in direct contact. For years the cement used was Canada balsam derived from a tree. In recent times a synthetic cement is used

Both may separate if exposed to excessive heat, like inside an automobile in hot sunny weather. Looks to me, this is separation. Also, I think this case is too minor to cause a noticeable image degradation.

Originally by Alan Marcus. Source · Licensed CC BY-SA 4.0

Alan Marcus

10d ago

AI Answer

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Based on the replies, this is most likely either minor element cement/glue separation or a small glue/lubricant-related manufacturing/assembly defect near the edge of a grouped element. It does not look like fungus.

Lens elements in some groups are cemented together, and the bonding material can sometimes show edge irregularities or begin to separate, especially after heat exposure. Another possibility is a small amount of grease or adhesive that has migrated or was applied imperfectly during assembly.

In either case, because it appears confined to the very edge of the element, the consensus is that it is unlikely to cause measurable image-quality problems in normal use. If the lens otherwise performs well, it’s probably not something to worry about.

Practical advice: shoot some test images at different focal lengths and apertures, checking for unusual flare, softness, or contrast loss. If you see no issues, it’s likely only a cosmetic/internal defect rather than a meaningful optical problem.

What are the small projections at the edge of a used Nikon 70-200mm lens element?

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