Heavy breathing in Nikon land

My old 135mm f/2.8  AI-S lens: still working, despite being breathed on

There has been much harrumphing on the forums this week in the wake of some technical advice from Nikon about cleaning lenses that was unearthed and posted on Petapixel. The advice was quickly reposted on several other blogs and forums, including Nikon Rumours, Photography Bay and DPreview. It runs ran as follows*:

How do I clean the camera lens?

The best way to clean a lens is to use a piece of lint free lens cleaning tissue and a small amount of Lens Cleaning solution. Do not use anything containing abrasives or  solvents, only use Lens Cleaning Solution.
First we recommend taking a small blower brush to blow off or brush away loose dust or debris.
Next, place a drop or two of cleaner on the tissue (never directly onto the lens) and then wipe the lens in a circular motion, beginning in the center and working your way outward, removing any marks or smear.
If the above supplies are not available a clean, dry, soft, lint free cloth can be used to clean the lens. Do not breathe on the lens to fog it for cleaning. There are harmful acids in breath that can damage lens coatings. Just use the blower bulb, then brush, and wipe the lens in a circular spiral from the center outward.
The same method can be used to clean the viewfinder eyepiece of Nikon cameras.

Read more on NikonRumors.com: http://nikonrumors.com/2012/12/07/nikon-support-do-not-breathe-on-your-lens-to-clean-it-your-breath-contains-harmful-acids-that-could-damage-the-lens-coating.aspx/#ixzz2EmKDsDB2
This leaves me in a bit of a conundrum. First of all, I've been using the "breathe on lens and wipe it carefully with soft lens cloth" technique for cleaning lenses for longer than I can remember, and certainly for more than two decades. When I first bought an SLR, I started to use lens cleaning fluid – much as recommended in this advice – and found it tended to leave smearing. In fact, the cure was often worse than the condition. I quickly went over to gently breathing on the lens, and using the condensate with gentle wiping: this has been much more satisfactory, and is my standard method to this day.

The second point is that far from being acid, I've always been led to believe that exhaled breath is actually slightly alkaline. (In case you've forgotten, pH 7.0 is neutral, lower numbers are acid, and higher numbers are alkaline. Wikipedia explains it clearly.)  A quick PubMed search confirmed this. Almost all breath from healthy people is slightly alkaline. There are some disease conditions in which the breath becomes acid (e.g. some infectious and inflammatory diseases), but most healthy people don't have acid breath.

One caution though is that before measuring the pH, samples are usually flushed with argon to blow off any dissolved carbon dioxide. So, in principle, there could be some variable amounts of carbonic acid in anybody's breath.

The thing is though, that dissolved carbon dioxide is a characteristic of any normal watery sample. So if your lens ever gets any condensation on it (e.g. bringing it back into the house after a walk on a cold morning), it could in principle be exposed to carbonic acid. Worse still would be rainwater, which usually has a pH somewhere between 5.0 and 5.6, but may get down as low as 2.0 ("acid rain").

Traditionally, lens coatings have been based on components such as magnesium fluoride and silica. These are pretty inert compounds, and it takes something like nitric acid (a strong acid) to dissolve magnesium fluoride. Carbonic acid (pKa ~ 6.4) is a weak acid. Now, I have no idea what Nikon use in their latest Nano-Crystal coating, but I would be amazed if it was any less inert than these kind of compounds.

So what to do? In general, I always try to go with the manufacturer's recommendations for any product. They're the ones who have spent time and money developing the best methods. But just for once, in this instance I am going to carry on doing what I've done for decades. It's probably true that a professional photographer with a medical condition that gives acidic breath, who needs to clean a lens several times a day, may progressively degrade it with the heavy breathing method. However, my experience over decades has been that moderate amounts of exhaled condensate are sufficiently safe for me to carry on as usual. Nevertheless - breathe on your lens at your own risk!



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*Update 11 Dec 2012, evening: the underlined bold advice on the support page has now disappeared. The acid prohibition has now gone! I wonder why?