Newtonians and Sea Air?

I live near the ocean, (about 1000 feet from the beach, not immersed in salt spray) and, so far, have done my observing with refractors. One concern that contributed to my refractor choice was that the marine environment might quickly dull the coating on a Newtonian primary. I'm not sure where I got this idea. Does anyone have first-hand knowledge?

Steve

from the moment of its conseption oxidation is taking place, and of course the salts in the air will speed up this process, just look at the metal objects in your invironment no look closely, corosion is there, the coating on a mirror is metal and vulnnerable. that is one of the resons i sold my 8" reflector and got a 6" long focus refractor. not to mention i have to go 40 minutes up the hill to get above the fog. john

I don't know about knowledge (didn't someone once say something like, "100 anecdotes still isn't data?"), but I live on an island, too, and have what I believe to be salt damage. When the mirror was new I went with the common practice of not cleaning the mirror too often, and keeping it covered. After a few months I noticed what I thought were mildew spots. They were about 1/8" -1/4" diameter and looked almost exactly like miniature sunspots. Another e-mail acquaintance who lives on an island described his spots as miniature Julia Set Fractal patterns. I have since come to the conclusion, after looking at them through a magnifying lens, that it isn't mildew, but corrosion from salt that is eating the coating from the back having entered through a pinhole. My coating is Beral, but our club's scope is coated aluminum and shows almost exactly the same pattern of spots. Before I saw it on the club's scope I was thinking that the SiO overcoat would protect and that I should eventually get mine recoated. But apparently even the overcoat can have pinholes for salt to intrude through. The spots don't wash off or even get better with washing - they are permanently etched.

My solution was to just clean the mirror more often, like just about once a month. I know that it's frowned upon in general, but since I've been doing that the spotting has stopped. I figure that as long as I'm careful I won't do much damage to the mirror, and it definitely can't be as bad. Just another anecdote ;-) but I hope it helps.

Doug Tanaka