15 year old AI-S lens - bright spots at certain angles looking at rear element.

[gooseberry]

Have an AI-S lens, about 15 years old now, it still looks mint and the glass is clean, however, I have noticed that looking from the rear, there are some bright spots that appear only when angled at a certain way with a light source.  (see pictures) Glass looks perfectly clear otherwise, and only on this small section - is it because of a defect in the lens coating ?

[Birna Rørslett]

A beginning fungus infestation? Try wiping with window cleaning fluid on a microfibre cloth.

Over time, fungus will "eat" the coatings thus important to remove as quickly as possible.

[gooseberry]

Thanks for the reply.  Yeah, I did try wiping with some lens cleaning fluid and a microfibre cloth - no change. Looking at it more closely, it seems to be on an inner surface, because the surface of the rear lens element is perfectly clear.  I hope it is not fungus.  I suppose the only way to tell would be to take it into someone who repairs lenses and see what they say.

[Snoogly]

What lens is it? Might be an easy DIY job?

[gooseberry]

It's a 35mm f/1.4 AI-S

[Erik Lund]

Here is a link to Richardhaw's repair of that lens

https://richardhaw.com/2019/08/07/repair-nikkor-35mm-f-1-4-ai-s/

If it's restricted to the rear lens element it's not to bad a diy job

[Snoogly]

Here is a link to Richardhaw's repair of that lens

https://richardhaw.com/2019/08/07/repair-nikkor-35mm-f-1-4-ai-s/

If it's restricted to the rear lens element it's not to bad a diy job

I just came here to post the same link and say the same

[Birna Rørslett]

If these dots or specks are on the inside, the likelihood of a fungus problem is high. Still as the putative fungal growth isn't excessive, it should be eay to remove once the lens is disassembled.

[Toby]

Dots like that are not fungus, which always has filaments of some sort. Two possibilities. First, and hopefully, there is lubricant that has vaporized and condensed on the surface of one of the inner elements. The rear part of that lens has six elements in three groups. The last two elements are air spaced, but the inner group in four elements cemented together. There is a possibility that there is delamination on one of the cemented surfaces. If that is the case, it is a real pain to recement four elements and get it anywhere near right. But it looks to be on one of the two elements near the rear, and that should not be a hard fix. OTOH, if the lens looks clear looking through it and those spots are only visible at an oblique angle, it is most likely delamination happening.

[pluton]

From the closest photo, the mystery spots and the rear bezel of the lens appear to be in the same plane of focus, which suggests that the spots are on one of the two rearmost elements.  If true, that could be good news. If the rear elements don't rotate as part of the CRC system, they might be relatively easy to extract..at least the rearmost element.  The outer element appears to held in by a simple retainer which can be [presumably] be unscrewed by a common lens spanner. See https://richardhaw.com/2019/08/07/repair-nikkor-35mm-f-1-4-ai-s/. If the rear group IS part of the moving CRC system, I'd advise more caution.
Personally, I'd give this to a professional, mainly because I genuinely dislike fiddling with small/tiny parts while not having exactly the right tools or knowledge.

[Geert]

My favorite method for removing fungus is to disassemble the lens and remove the glass element that is affected. Put that element in a beaker glass containing a solution of 50/50 ammonia and hydrogen peroxide. Wipe clean with cotton cloth, lens wipes, soft paper, a soft brush... anything that will not scratch the glass. Then rinse thoroughly with demineralized water. Leave to dry. Before reassembling, put the treated lens element plus the exposed inside of the rest of the lens under a strong UV-lamp for 30 mins or an hour or so, to kill off any remaining fungus traces or spores.

I did this many years ago on a Nikon 105mm f2.8 AF-DC that had some fungus inside. The fungus was gone completely and it never came back. Still the sharpest lens i have.

[gooseberry]

hi all, late reply as I took this to a nikon lens repair specialist over a month ago to check it out.  They finally had a chance to look at the lens.  It was not fungus but optical glue separation. To repair would require parts.

[bressong]

hi all, late reply as I took this to a nikon lens repair specialist over a month ago to check it out.  They finally had a chance to look at the lens.  It was not fungus but optical glue separation. To repair would require parts.

sounds like the right answer

it needs a big surgery then