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Maintenance & Repair of Lens optics


Active Member
Hello Everyone,

Last week i was quite shocked to see fungus growth on the rear element of my Sigma 18-50 F2.8 lens. It was quite small, about 2mm or so. Nevertheless i was worried as fungus does irreparable damage to lens optics.

Its actually my mistake that i did not perform preventive maintenance on my equipment after a long and extensive tour just a month back.

I would like to share two links which i referenced to help me with my problem:



Both reference Carl Zeiss who in my opinion are one of the best in optics engineering if not the best :)

The first one is a 1905 manual :) and the second is a very current link to Zeiss Germany service and support page!

Personally, i used the cigarette ash method for my current lens problem as using straight micro-fiber cloth did not work, so was the case with breathing on the lens and distilled water. (I did not have naptha handy.)

Cigarette ash worked like a charm :) lens is now as good as new and now i intend to ensure that this does not happen again!

Hope this information is useful to you in maintaining your lens optics!

Thanks and stay well.

P.s: In my search for relevant information i came across exotic techniques to clean and repair lenses...some utilizing cold cream and kerosene!!! Can anyone explain how these work to clean lenses?? Not that i am going to try them on my lenses :)
Hi Sendhil and welcome to the forum! :)

Though I am no expert on fungus problems ... I once had the problem with a 400mm Beroflex telephoto-lens that became wet in a cold cellar.
I put it to pieces then (not as complicated as with modern lenses) and simply polished the affected lens-units. That treatment was successful. I frequently use this lens with my SIGMAs now. :)

See you with nice pictures

Hello Klaus,

How did you polish the lenses? Can you detail the procedure please! I am very interested in knowing about this procedure :)

Also to add to my original post, the Schneider manual recommends saliva as a perfect cleaning fluid!!

To quote "Always available, guaranteed free of abrasive materials, oil and aggressive chemical substances"

I guess sometimes the best things in life are 'really' free :)

Thanks and stay well!
Hi Sendhil,

as mentioned ... I am no expert on the issue. Since the old Beroflex is no expensive lens to be replaced, I was courageous enough simply to use a smooth cloth wetted slightly with a bit of isopropyl.

I am not sure, whether there are better ways probably more gentle towards the lens's coating.

However fungus is said to destroy lens-coatings anyway .....?!

My result was good. The Beroflex looks clean since and works very well.

By the way ... the Beroflex' range (300mm/400mm/500mm) is an insider's tip for very cheap and high quality telephoto lenses. :)

See you with nice pictures

Thanks Klaus!

And i have noted your "insider tip" for the Beroflex lenses :) though at the moment i am working on understanding how best to use my recent M42 lens purchases!

Stay well.