A mild bit of controversy over the weekend in the Nikon world with a December 7 blurb about cleaning your lenses on Nikon USA's support page. The original text went like this:
"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."
The is posting was updated on December 10, 2012, with the underlined text removed, but not before it made the rounds with Nikon Rumors and PetaPixel.... and drawing the predictable ire of the comments sections on both websites. The more suspicious out there tended to see this as a ploy to scare people into buying lens fluid, whereas your breath is ostensibly free. Darn those evil corporations!
Depending on how you react to the printed word, your first reaction might have been to resolve to duly hold the camera away from your mouth at all times henceforth, or it may have been to immediately scoff at the poor soul who put this wording up on Nikon USA's site. Since they eventually modified it, I'll let you figure out which reaction would have been the appropriate one to take... Still, this raises two questions for the curious: is your breath acidic and would it in any way be harmful to the coatings on your lenses?
To answer the first one, you would have to account for the physiological reasons about how your breath could become acidified in the first place. I can think of two, so we'll get the less plausible one out of the way: If you are suffering from acid reflux, some of your stomach acid can conceivably make it's way out of your esophagus and into your throat, where it mixes with your exhaled breath and becomes microscopic droplets in the air stream. Since I'm sure Nikon USA was thinking about healthy people when they wrote this, we'll move on to reason number two.
As you are probably aware from high school biology, humans breath in oxygen and breath out carbon dioxide as metabolic waste. Carbon dioxide is fairly soluble in water and your lungs have the surface area of a mid-sized apartment where the blood vessels in the alveoli come in direct contact with the atmosphere. Since your body is mostly water and the lungs constitute a very large surface area, your exhaled breath is saturated with water vapour, and since it is mingled with the C02 diffusing out of your bloodstream, some of it will dissolve the C02 to form carbonic acid which is acid. Actually, it's only mildly acidic, but we'll gloss over this for a moment.
Now for a bit of human physiology (and a hazy trip down memory lane for me... PHYL 301 is a complete blur now). Your blood carries C02 in dissolved form (CO2 + H2O H2CO3) through the action of the enzyme carbonic anhydrase, which is one of the fastest acting enzymes in the human body. This is unlike oxygen which is carried on the hemoglobin molecule and not dissolved in the blood plasma. When it reaches the lungs, the carbon dioxide returns to gaseous form and exits your body. It might be possible that the water vapour exiting your lungs stills carries some dissolved carbon dioxide, or that that CO2 leaving the alveoli can redissolve in the water vapour before it exits your mouth but.... Have you ever noticed that you can pour a glass of soda (or beer if you are so inclined) and the carbonation won't immediately rush out of the drink, but that when you take a sip the liquid immediately bubbles in your mouth? That's carbonic anhydrase again: it's present in your saliva, and as your exhaled breath moves through your mouth, the enzyme is (probably) un-dissolving the last of the carbon dioxide into the non-acidic gaseous form.
However, the proof is in the pudding, which brings us to this medical paper: http://www.ncbi.nlm.nih.gov/pubmed/21600044. Although it is not specifically a paper about breathing on camera lenses (that would be too much to ask), the authors did measure the pH of the breath of various test subjects and came to the following conclusions
- Healthy Person: pH 7.5
- Smoker: pH 7.24
- COPD Patient: pH 7.21
So you can see why Nikon USA pulled the wording on their article... they were unintentionally implying that breathing on your lenses to clean them is worse than taking your camera out in the rain! I'm sure a few adventure photographers had a laugh when they read Nikon's recommendation. That said, I'm going to give Nikon the benefit of the doubt here. If you are huffing on your lenses to clean them with the loose edge of your shirt, that's probably bad. If you live in Canada like I do and your shirt is the obligatory red flannel lumberjack, then that's doubly bad. The other thing about the condensation from your breath is that it doesn't dissolve oils, hence the recommendation to use lens cleaning fluid which is usually a mild alcohol dilution that will dissolve oils and other non-polar materials. This is also where a good microfiber cloth comes in, as it has the microscopic surface area to lift the debris away from the lens, and will absorb oils.
Just one final thought about a bit of advice that I got from a pro when I was a teenager obsessed with keeping my camera spotless... don't worry too much about it, just go and shoot. Your camera was made to be used.