Lens Internal Crack (Delamination)

[Steve Bellayr]

I have a lens, an collapsible Carl Zeiss Jenna 50mm f2.0 that I picked up recently that appears to have a "crack" on the outside of an inner element. You can on only see this defect (which someone suggested it could also me a delamination) when the lens is wide open. Since I have no intention of repairing it has anyone used a lens with a crack or delamination and what were the results?

 

[sevo]

"On the outside"? Does the supposed delamination extend into the glass? If it does not, it will be the edge paint flaking off, which is a fairly minor issue.

 

[Steve Bellayr]

From your answer let me clarify. It is most probably a crack in the glass at the edge of an inner element as I do not see anything flaking off. How will it affect images?

 

[sevo]

From your answer let me clarify. It is most probably a crack in the glass at the edge of an inner element as I do not see anything flaking off. How will it affect images?

Paint peel will cause the (normally black painted) edges of some elements to appear silvery or white, or to develop white specks. It is far more common and tends to be more visible than either element separation or glass cracks (which both will usually only be visible at some angles).

Paint peel is generally harmless - it can only affect flare and can be controlled with a lens shade.

Cracks in inner elements are rare and often only discovered when the lens is taken apart. If the lens is properly mounted and all pieces stay in place it will not affect the images beyond increased flare sensitivity, but if the element has been displaced, that may change the optical properties and mess with focus and correction of the lens.

Element separation often is visible as "dirt between the elements", if it a side effect of cement rot or drying up of older Canada balsam cement. But if it was mechanically caused by strain or shock, it will often be invisible. Depending on the lens design, it will often be as irrelevant as one extra pair of uncoated internal surfaces, but in some cases a unintended microscopic glass/air/glass gap may cause significant changes in focal length or correction.