Quote Originally Posted by keithwms View Post
Ed, water is just about the very worst thing you can use on any lens. First of all, the lens surface will be hydrophobic, so water will not spread evenly, and moreover the [inevitable] contaminants in the water will immediately precipitate out onto the lens. Also, some of the AR coatings make this issue even more important. Finally, the most deleterious substance on your lens would be oil, against which water will do no good at all. If you must use water then you must also add surfactant or you will probably make matters worse.
... And the first raindrop falling on your hydrophobic lens (not protected by a UV ... or... barrier) will render it ... what? Useless? Let me redirect you to what I wrote - the important part is DON'T!! if at all possible.

Since I am already being a contrarian in this post, permit me to also disagree with your assessment that a damaged Leicablad lens is the saddest sight in all of photography.
Go ahead - disagree!! You are perfectly entitled to do so.

To me the saddest sight in all of photography is a fantastic lens with a UV filter on it. IMHO a person who is willing to pay the bucks for fantastic lens should also be willing to take the risk of letting the lens do what it can, in all its naked splendour.... as the lens engineers (and indeed, God Himself) intended for it to be used.
??? - WHO intended what??? I'll agree that the Optical Engineers were involved - I've known and worked with a few.
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Uh ... Permit me to say that it somewhat presumptuous to assume the intent of the Great Creator. Possibly, in some grotto, on some Chapel ceiling ... we might discover a painting of the GREAT ZOT ripping a filter from a lens amid flashes of lightning and thunderous peals of thunder - so far I know of none even remotely applicable. Until I do, I'll limit any discussion to the engineers.

While I'm at it - I have never encountered ANY optical engineer with such a negative evaluation of filters. Period. As long as the geometry of the filter is reasonably sound there is/ can be - VERY little effect on the ray tracing and finally, image. Way back, I was presented with the idea that the thickness of a filter had a negative effect on image quality. As an experiment, I set up a lens on the optical bench, observed its characteristics - and introduced what would be an unreasonably thick filter, in the form of a double surfaced fused quartz optical flat. Fused quartz, with a HIGH refractive index, complete with "seeds" (small), and -- ~ 40 - 50mm thick. End result? No ... NO significant degradation of image quality.

Now ... Water is not appropriate for removing oils. True.
In trying to remember, I can't think of any instance where I have encountered oil contamination, Must be that my (demon) UV filters are woring well.

But then - there are those who would advocate the use of Drano and a grinding wheel...

We did have one techni ... uh, well not quite ... who decided to clean a lot of 20 specially coated (20 layers) lenses... his choice of cleaning media was a common pencil eraser.

He never got a second chance.

BTW ... Surfactant? Wouldn't that decrease the surface tension and increase the possibilty of accidental incursion ito the innards of the lens?