Cooke speed Panchros: Fungus cleaning

[omar robles]

Hello Group:

My buddy is selling me a 32mm COOKE SPEED PANCHROS. The problem is he said it has some fungus on it.  He thinks he can clean it but isn't sure. His fear is damaging the coating on the cooke lens.  Is this a job that a average person can do or does it require a specialist? Does hydrogen peroxide or vinegar work?

 

 

[Dom Jaeger]

If your friend is not very experienced with working on lenses, and the lens is in any way valuable, then get it properly cleaned by a professional.

Lens service is not something you can generally DIY unless you don't care about the lens and you want to learn. But I wouldn't be practicing on a Speed Panchro worth thousands. Start with junk lenses that cost nothing. 

Depending on the age of the lens, the coatings may be soft and easily damaged. The lock rings may be hard to undo, making it easy to slip and scratch the glass.  To properly access every element you usually need to dismantle the optical block from the focus mechanics, which is not a job the average person should undertake. There may be cemented doublets with haze or fungus in the join, which will not be cleanable without splitting, which is definitely not a DIY job. 

 

[Mark Dunn]

If it's on the front or back surface- it's easy to tell- you could try isopropyl alcohol. I cleaned a 'Scope adapter this way once. You may be lucky if it's the right sort of fungus, and used sparingly you won't cause any damage to the lens or yourself- IPA is much nicer than peroxide.

Edited June 15, 2023 by Mark Dunn

[Robert Hart]

My sense is to respect the lenses and have the work done by professionals who know what they are doing. Before I knew their intrinsic worth, I de-fungussed  two Speed Panchro Series II lenses. They had been assessed as uneconomic to repair and were a gift. The 50mm was fairly straightforward but one of the internal optics had a little penetration into the glass. The front coating cleaned up well enough.

The 75mm was a basket case with small but noticeable scratches on the front element from careless cleaning and one of the internal elements had penetrating fungus erosion of the glass itself. I made a sort of conforming mould and polished the eroded glass with cerium oxide. By more dumb luck than good judgement it worked. On reflection and from reading I have done since, it was something of a minor miracle that I did not destroy the figure of the element.

Both lenses ended up flarey, the 75mm more so. Outfits like P+S Technik apparently polish and recoat the glass of the lenses they modernise. This is of course a costly exercise.