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Lens cleaning/restoration help for a friend in India

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I got an email from a friend in India this morning about a lens he got cheap, but with fungal damage.

Here's the email.

"Need some help in one of my recent projects as I've hit a stumbling block.

I recently acquired an air-spaced achromatic triplet to build a wide field astrograph - 155 mm dia. I got it relatively cheap as one of the lenses had some fungal damage. I spoke to a local camera repair shop and they said they could polish the surface to remove the fungal damage.

However, when I received the lens, I found the surface to be noticeably uneven. Can you please take a look at that and give me your opinion if this is something that can be further repaired or if this thing is now a waste? If something can be done, then what? Further polishing?"

The attached pictures don't show things that well, but I've attached them any way.

post-20257-0-69437600-1376851203_thumb.j post-20257-0-99084500-1376851224_thumb.j

He's after a second opinion as to whether polishing will sort it, or whether the camera shop is just looking fo money out of him!

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Firstly, it is difficult to tell from the photos precisely what, or where, the damage is. I would try the lens out first to see if the damage is having an unacceptable effect on the image. If so then some remedial work is required.

If the damage is on the outer surfaces I would approach this by first carefully cleaning the outer surfaces with a propriety cleaning fluid ( Baader Wonder Fluid gets a good report here ) or IsoPropyl Alcohol.

If the damage is on one, or more, of the internal surfaces then the lens will have to be dismantled. The lenses must be carefully marked on their edges so that they can be re-assembled in exactly the same position as they are now and that includes returning the spacers to the same positions. Make sure that the spacers are not mixed together as the separations of the three lenses might be slightly different. The surfaces can then be cleaned.

If it is not possible to clean them satisfactorily then re-polishing might be the final option. It might be worthwhile to get the opinion of a company that does the anti-reflection coatings as it might just be that replacing the coatings alone will work.

Good luck in getting this sorted.


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