I was recently asked to be a guest on the Classic Lenses Podcast. It was a very enjoyable experience and I was asked a whole multitude of questions regarding repairs to lenses. Feel free to listen to it in all its glory here.
A subject of major interest was the dreaded fungus infection of lenses and my recommendations of how and what to treat it with. This led to a further discussion on the Photography With Classics Lenses Facebook page, about the various different cleaning products that people use. I personally use a cocktail of things (trade secret) that was mixed up many moons ago and has served me well. However I have been asked on more than one occasion about the merits of using Hydrogen Peroxide to remove fungus, so it seemed the time had come to try the stuff for myself. Someone was kind enough to provide me with a link to an Ebay listing for the very stuff they use (Hydrogen peroxide 3%) and I ordered a small amount there and then. What follows is my comparison with another easily available product (sharing some properties of my own mix) standard window cleaner with a vinegar content.
Anyone who wishes to use these or any other chemicals to clean optics please be aware of the risks involved. As such I do not take responsibility for anyone who copies me and ruins a lens (i.e don’t try this at home) If in doubt, send your lens to a professional repair person such as myself.
This shows two optics taken from a Pentax 50mm f1.7 SMC PK lens. The top surfaces have fungus on them but the under sides have already been cleaned to make it easier to see what effect cleaning has.
The left optic was cleaned with window cleaner and the right optic Hydrogen Peroxide 3%. I applied the cleaners with a cotton bud and gently massaged it over the surface. The first thing that struck me was that the Hydrogen Peroxide seemed to cling to the fungus affected areas, almost pooling over them, in contrast the window cleaner covered the surface pretty consistently. I then washed them with clean water, blew them dry with compressed air and buffed with a chamois.
In both cases the fungus is gone but there is some coating damage on both. This was not unexpected as the lens contamination was quite bad and had been there a long time. I have cleaned many of these Pentax 50mm lenses and the coating marks are consistent with what I would expect using my own cleaning products. But, I was impressed with the Hydrogen Peroxide as it appeared to actively destroy the fungus on contact.
Next I wanted to try each product on the same optic, to rule out any possible differences in coatings.
Here we can see the underside of the front optic from the same Pentax 50mm lens. Both areas of fungus are very similar so a fair test of the products.
Again, the left side is treated with window cleaner and the right Hydrogen peroxide. I only treated the infected areas, you can see the Hydrogen Peroxide clinging to the fungus while the window cleaner is already starting to evaporate (I had to rub it much more as you can see)
I then washed the optic in clean water and dried it with compressed air.
As there was still some water marks and smudges I then cleaned it with a chamois.
As you can see there are still outlines in the coating of where the fungus was. Most people would struggle to see these imperfections and once assembled even more so.
The Hydrogen Peroxide seems to be a more efficient way to remove the fungus but is very poor at oil or finger marks. The window cleaner is a much better overall cleaner that just requires a little more effort to remove the fungus. Therefore I must conclude that the best results will be had from first treating the fungus with Hydrogen Peroxide then use the window cleaner to clean/polish the optic.
Of course, this is but one stage in repairing a lens and you will still have to reassemble it in the correct order without getting finger marks or dust in between the elements etc.
Please be aware that I have not tried these products on all lenses and coatings, some may react in an undesired way with your own lens optics. If in doubt send to a professional repair company as it is very easy to destroy a lens.