Fungus question

[Gogster]

I've been offered a Canon 300mm f2.8 IS USM for a very good price. The seller has informed me and I've inspected the lens and it does indeed have a miniscule bit of fungus on one of the elements. I have done some searching on the internet and it's a bloomin minefield.

I'm looking for genuine knowledge in this field, rather than anecdotal please, can anyone tell me:

1. Can these weather sealed lenses be cleaned effectively?
2. Does cleaning damage the coatings?
3. Once cleaned, is that the fungus gone forever or will it always be susceptible to fungus and it may come back?

Thanks in anticipation.

 

[PhilH04]

1. Can these weather sealed lenses be cleaned effectively?

Yes..

2. Does cleaning damage the coatings?

That I am not 100% sure on, but I would imagine the cleaning itself wouldn't, @StewartR may know more on this subject than I.

3. Once cleaned, is that the fungus gone forever or will it always be susceptible to fungus and it may come back?

It will all depend on storage etc. Weather sealed does not mean airtight...

The caveat here as I am sure you are aware is for any cleaning to be done by a good technician.

The other is how bad it is, there is a fairly good chance that there will be no effect on the image quality and preventing any further growth is all that may be needed.

 

[Mr Badger]

Fungus can sometimes permanently 'etch' the coatings of lenses and the surface of glass, so it may not be possible to remove all traces of the effects of lens fungus.

I know fungal spores are reputedly floating around in the air all the time in most parts of the world, and they require the right conditions in which to grow, but there are many types of fungus not just the type that can grow on camera lens elements. So I wouldn't want to encourage lens fungus spores into my home, camera bag, camera internals, etc. I may be worrying unnecessarily here, but sometimes I think it's better to avoid the cause of worry if this is a reasonable option! Therefore I wouldn't knowingly buy and use an interchangeable lens with fungal growth on it, that way it can't cross-contaminate my kit with spores. They may already have a dusting on them as part of the natural environment, but I don't want to increase the probability if I can reasonably help it.