Curious lens damage

[leonardturner]

Inspired by the recent posting by another member, I pulled out my elderly 63 mm El Nikkor recently, only to find the front surface apparently quite dirty. When efforts to clean it failed, I took a closer look and found the interesting pattern shown here.






An even closer look revealed that the damage was not on the surface as originally thought, but apparently between elements close to the front surface. Examination with a 10 X objective produced these images made with diffused LED through the back of the lens, full frame first image, cropped version in second:




And these made with diffused strobe at an acute angle to the lens front:





I take this to be fungal from its appearance, perhaps on an internal glass to air element (does fungus ever grow between glued elements? I don't know). Incidentally, there seems to be a massive amount of CR in the last cropped image (MRL00102 Nikon on a Raynox) as well as a lot of flare (coma?) Is this real or an artifact from the overly lit elements in the image--again, I don't know. Interesting.

[rjlittlefield]

Incidentally, there seems to be a massive amount of CR in the last cropped image (MRL00102 Nikon on a Raynox) as well as a lot of flare (coma?) Is this real or an artifact from the overly lit elements in the image

My guess would be that it's from looking through a glass element to image the subject. 10X NA 0.25 is not very tolerant of looking through dense medium, and even less so if the medium is non-planar or you're the slightest bit off perpendicular.

--Rik

[ray_parkhurst]

Yep, that's fungus. It's likely that fungal spores either fell on the surface of the lens element during assembly (if the surface you're viewing is in an air gap between lenses) or fell into the balsam and got evenly distributed during mixing (if the surface you're viewing is cemented). It looks like only a single species of fungus is present, so the contamination probably happened in a relatively clean environment.

edited to add:

I generally see more fungus between cemented elements than air gaps. The balsam is fungus food. In air gaps, there is not much food, though fungus will grow on dust particles if present. This is a good reason to keep your lenses as dust-free as possible, and as dry as possible. Fungus needs food and moisture to grow.

Looking at your lens again, I would bet it's an air gap, and the centers of each colony were fungus-infected pieces of dust that landed there during assembly.

[leonardturner]

My thanks to you both. This really helps my understanding, and I appreciate your comments.

Leonard Turner

[Asha]

Leonard, even with dust and fungus, the lens still might be quite useable. If the lens design does not have an internal image near the defect, and/or if the defects are near one of the pupils, the effect will be difficult-to-impossible to see on captured images.

ETA: there could be an increase of stray light due to the defects, but it would be difficult to say how much without simply trying the lens and see if it is a satisfactorily low amount when devices to minimize stray light are also used.

[jjphoto]

Yes. Fungus.

It also significantly devalues a lens, regardless of it's affect on performance.

[leonardturner]

Thanks jiphoto and Asha. Devaluation if of little import since I only paid some $35 for it some time back and had no plans to sell it (and certainly would not offer it in its present unhappy state). Asha, I was aware that the lens might still be usable, but your comments gave me the impetus to try it on this Saturday afternoon. Both of these images are full frame (Nikon 810); the fossil shark's tooth measures about 1 cm from tip to root. The postage stamp was shot with more bellows extension, about 3X. Both look reasonably good. Doubt I'll ever shoot with it again, but this was an interesting trial.

[Asha]

Leonard--nice! Thanks for following up

[Lou Jost]

Nicely contrasty! Fungus often drops the contrast due to scattering light into the dark areas. Your blacks look quite dark. I bet if you avoid strong backlit scenes the lens will be just fine.