Sunday, December 30, 2012

 

Mirror Cleaning Madness


Do you frequent the Cloudy Nights bulletin boards, muchachos? If you do, you've probably noticed Unk dispensing mirror cleaning advice. That advice, for those of you who don't do the CN forums, usually consists of one word:  "Don't." Oh, I amplify on that a wee bit, telling the questioner that every time you clean a first surface mirror you run the risk of doing more harm than good. That's what Unk was taught as a novice astronomer, and it is still somewhat true, but if pressed the Rodster will now admit cleaning a telescope mirror is not always an idea that springs from the depths of Hell.

One thing that's changed in the last half century is that most telescope mirrors now have pretty good overcoatings. I don't mean to say you can get out a Brillo Pad and give your primary a good scrub to remove that misbegotten spot of squirrel poop. But at least you don't have to worry as much about destroying your mirror's coating or leaving a bunch of "sleeks" (small scratches) as you did in the day when it wasn't unusual for a mirror's reflecting surface to be formed by a thin and fragile chemical deposition of silver that had no protective coating at all. Sometimes, following unexpected disasters like the depredations of Mr. Squirrel, you just gotta clean a Newtonian reflector's mirror.

Cleaning is maybe also more needed these days because, unlike when Rod was a little feller, we are much more prone to do all-night observing runs (3 a.m. in the case of your aged Uncle) than we were back in the hallowed Day. A few hours in a tree-shielded backyard meant it was unlikely the primary would attract dew. Today, go all night on an open star party field with the scope left out till dawn and the primary will probably wind up a soggy mess. Why does dew make mirror cleaning more needful? Air pollution, campers.

It ain't like we didn't have air pollution in the 1960s and 1970s—the air is undoubtedly cleaner now—it's that dew, which can be loaded with airborne pollutants, didn't often get on the mirror for the above reasons. The picture up top shows Old Betsy's mirror after a few nights at the Deep South Regional Star Gaze. When it dried, the dew bath left behind nasty streaks aplenty. Did these streaks affect images? No. Not to any noticeable extent. If it were just a matter of the mirror not looking clean and pretty I wouldn't have cared pea turkey. The reason I cleaned Betsy's primary was that I was worried about damage to the coating from unknown contaminants. It's possible dew includes a ration of pollen as well, which is abrasive, and not much of a Good Thing.

Yes, today's mirrors are comparatively well protected, but those overcoatings are porous on the microscopic level, and if the stuff the dew leaves behind on the mirror is nasty enough it might eventually do damage, especially after it is soaks in following repeated wettings by more dew. Is this a huge concern? Probably not, but I paid a significant number of buckeroos for my super-duper coating from Spectrum Coatings (recommended), and I want to preserve it for a while. So, I cleaned my mirror and I am going to show you how to clean yours in relative safety.

Eventually. Before we get to that, let's do one other thing—Uncle Rod's Year in Review. That, like the Christmas Eve blog, is a tradition 'round here. I thought about skipping it this year and getting straight to the distilled water and Kleenex, but it won't take long to clean Unk's 12-inch mirror and there is something to be said for tradition.

January 2012

January opened, as I mentioned last time, on a sad note with the loss of our old buddy George Byron. Miss Dorothy and I soldiered on, of course. What else can we, the living, do? Anyhow, the big event of the month astro-wise was our traditional after-Christmas trip down to the Chiefland Astronomy Village. That followed immediately on Unk's return from an excellent speaking engagement in Portland, Oregon, and was especially notable because we'd replaced the old Stellacam 2 black and white deep space video camera with a fantastic Mallincam Xtreme.

Unk had got the camera a couple of months previous, but, naturally, the weather gods had seen to it that I hadn't been able to do much with it till we got to the CAV. In other words, Unk didn't know a cotton-picking thing about running the Mallincam. My images a year later are miles better, but from the first I was blown away by what this little camera could do. I mean, the dadgummed Horsehead in living color? In 28 seconds? Get out!

February 2012

The February blogs included everything from Unk getting his 12-inch Dobbie, Old Betsy, out of mothballs (high time) to one of his patented nostalgia trips; this time to ALCON 2003. The standout, though, was the entry on the last two nights of Unk and Miss D's January Chiefland adventure That trip was memorable for a couple of things in addition to the new Xtreme. We discovered the beautiful Manatee Springs State Park, and—the real biggie—Unk was beginning to see the light at the end of the long, long Herschel Project tunnel.

March 2012

March dang sure came in like a lion with clouds and generally icky weather. For that reason, the month's blogs were composed of more of Unk's patented navel gazing nostalgia. One I particularly liked was the piece I did to mark the passing of Norman Edmund, a huge figure in the amateur astronomy of the 60s and 70s.

April 2012

The bad weather and Unk's trips down memory lane continued, with me tending to agree with Mr Eliot that April is indeed the cruelest month. Did get some semi-clear skies, though, and I ticked-off some of the relatively few remaining Herschel objects, if not as many as I would have liked.  Night 32 of The Project, the second run of the month, was plagued both by gear problems and that consarned skunk ape and his pals, The Little Gray Dudes from Zeta Reticuli 2.

May 2012

May was a busy month, with me and Miss D. journeying to one of our fave vacation destinations, Rocket City, Huntsville Alabama. Chipped away at the remaining Herschels that month too, whittling away the stragglers, which were mostly little Coma – Virgo galaxies. The coolest thing for Unk, howsomeever, was finally getting off his rear and putting his Ultima C8 back together. Sorta, anyway.

June 2012

With The Project nearing its end, Unk was rewarded with a real good night that included not just another supernova to add to his collection of images of exploding stars, but a supernova in a Herschel object. "Synchronicity," I calls it. It was also the first outing for the little (tiny) Orion digital video recorder that replaced the humongous home DVD recorder and the monstrous inverter I formerly used for recording video. Other than that, the most notable event in June was our observation of the Venus transit from Fairhope Pier. We saw it, yeah, if only barely.

July 2012

July was quite the month. Unk had a fantastic birthday and he knocked off the last of the Herschels in Chiefland just in time for the publication of his big Herschel Project article in Sky and Telescope magazine. Not unexpectedly, I was at first ecstatic to declare victory over the aitches, but was soon feeling let down. Oh, there would still be fuzzies to re-image and sketch, but the thrill was undeniably gone. The cure? A new project that you will likely hear about next month. 

Anyhoo, it was a good trip despite rain and high temperatures. Unk not only got the last of those consarned galaxies, I got the pictures, terrestrial and celestial, I needed to go with another S&T piece I was working on. Only bummer? For the first time in years Dorothy wasn't with me; she was up in DC visiting daughter Beth. The best thing about this year's CAV trips was not the Mallincam Xtreme, wonderful though it was; it was having D. with me.

August 2012

August was something of a lay-off month for Unk astro-wise. Due to the demands of his daytime engineering gig, he had to, sadly, bow out of his usual trip to West Virginia to speak at the Almost Heaven Star Party. The skies in The Swamp didn't encourage much of anything when it came to observing, and Unk was in the doldrums with the end of the H Project. The August blogs were a motley crew, that's for sure. One I do like, still, is "Southern Nights," the story of summer deep sky observing with a small telescope down in The Swamp in the 1960s.

September 2012

 September came and saw me and D. back on the road to the Chiefland Astronomy Village, but this was to be a different sort of CAV expedition. No cameras. No big SCTs. Just a good old C8 and our Atlas mount. I wanted to do a little Herschel object sketching (if The Project ever does turn into a book, I'll need those) and test the Atlas' new firmware. This run also allowed me to (finally) get under dark skies with my enormous Zhumell binoculars and the mount D. and I built for them. Conclusion? I am not obsessed by giant binoculars, but I had a great time with them Down Chiefland Way and saw quite a few deep sky wonders in an entirely new way.

October 2012

The October blogs were, once again, a diverse lot, with the winner probably being the story of Unk's never-ending quest to take the perfect (within his modest expectations) image of M13. Otherwise? A little on the current states of ham radio and amateur astronomy, and, in recognition of the coming of fall star party season, a primer on the "how you gonna act" part of star partying.

November 2012

The big, big event for November was The Deep South Regional Star Gaze. It was an especially huge deal this year, since Uncle Rod had to miss his Home Star Party in 2011 due to the freaking day job (that may never be a problem again...more on that in a month or three). DSRSG XXX was not perfect, what star party is? But it was dang close to it. There were other blog articles on other stuff in November, of course, but November really was DSRSG.

December 2012

In addition to the yearly Christmas Eve blog you-all just read, December featured the revival of a small observing project of mine, "Unk's Messier Album," wherein I observe the objects in old Chuck M's catalog and compare what I see with what John Mallas saw and recorded in his landmark book, The Messier Album. There was also an account of our trip to the U.S. Space and Rocket Center for our Thanksgiving getaway. All in all, a good if mostly quiet month to put the cap on yet another year of The Little Old Blog from Chaos Manor South.

Now, finally, on to the purported subject of this blog entry, cleaning your pea-picking mirror. Before we get started, I will say it one last time:  Despite modern mirrors being protected by overcoatings, you are well advised to leave your mirror alone if it doesn't need cleaning. Stains and streaks left by dew are one thing; motes of dust are another. Dust will not harm your images. It will always be there. Any mirror will look horrible if you examine it under the oblique light of a bright flashlight. Unless there is a specific reason for cleaning, as in Unk's primary's repeated dew baths at DSRSG, confine yourself to, at most, a once-a-year mirror washing. In other words:  LEAVE IT ALONE.

After those scare words, the actual process of cleaning a mirror is going to be disappointingly anticlimactic. First step, natch, is removing the mirror from the telescope. If you have a truss-type Newtonian, that usually involves nothing more than releasing/removing some safety clips and carefully lifting the mirror off the sling and out of the rocker box. Solid tube telescope? Usually, it will be held in place by three clips. Loosen or remove them and carefully lift the mirror out of its cell.  You'll probably have to remove both mirror and cell from tube first, natch. Whatever kind of scope you've got, it might not be a bad idea to mark the mirror's rotational orientation on the cell and on the mirror's side to make collimation quicker, at least, after cleaning.

What if, like more than a few imported telescopes, your mirror is glued into its cell by silicone stuff? You have two choices:  clean the mirror in the cell or break the silicone loose (using a wire to cut it is usually the best way to get the mirror out). I prefer to clean the mirror in the cell if possible. Some imported truss tube scope mirrors are glued into their cells, and these cells cannot easily be removed from the tube. What then?
It is perfectly acceptable to clean the mirror in situ in the mirror box. A spray bottle of distilled water can make the process a little less messy, but it is not a big deal. When you are done, just dry the rocker box. Dob guru Dave Kriege cleans mirrors this way, I believe. Frankly, this is probably the easiest and safest way to clean a large mirror, even if it can be easily removed from the scope.

Mirror out of telescope, the main thing is DON'T DROP IT AND DON'T BUMP IT ON ANYTHING. Trot it into the kitchen where you've laid out your supplies. Said supplies are a gallon of distilled water, a box of Kleenex (original Kleenex, white, no lotion or scent), paper towels, detergent, and a bath towel.
The perfect place to clean a mirror of 12 – 16-inches aperture or less is in one-half of a double kitchen sink. Big dog? If you are going to remove it to clean it, I guess a bathtub would work, but, as above, cleaning in the scope is probably the way to go. Anyhow, spread a towel out in the sink bottom/side leaving the drain free, and rest your mirror against the towel padding the side of the sink, arranging it so it is not likely to slip (the towel with help prevent that) at an angle great enough for water to drain off its face freely.

OK, time to clean. Begin with a tap water rinse. I like to use the sink sprayer. Give the mirror a real good wash-down with the spray, being careful not to touch its surface. If your problem is just a year's accumulation of dust, this is likely all you will have to do, but if it's got remnants of dried dew like Unk's mirror did, you'll have to kick things up a notch. Do that with a cleaning solution. You will find all kinds of formulas on the Internet, but what I use is good, old Dawn dish-washing (hand dish-washing, that is) detergent. Make up a nice sudsy solution in a quart or so of water. It won't take much Dawn, but you don't have to obsess about getting too much soap in the solution since we will rinse the mirror very well .

Time for the scary part, scrubbing the mirror. Actually, you don't scrub, you swab, with Kleenex dampened with the Dawn solution. Some folks will tell you to use USP cotton balls, but I think Kleenex is better. It is softer and easier to get. Pour cleaning solution across the mirror surface and, APPLYING NO PRESSURE, JUST DRAGGING THE KLEENEX ACROSS THE MIRROR'S FACE, swab it from center outward, rotating the tissue as you go and changing tissues frequently.

When you are done, observe the mirror's surface critically. Does it look good and clean? If not, grab more Kleenex. Stubborn spot? If you have one and it doesn't disappear after a couple of cleanings with maybe light pressure with the Kleenex, my inclination is "leave it alone." It is less likely to cause trouble than you might by really bearing down on it with a tissue.

When the mirror is cleaned to your satisfaction, begin final rinse number one. Use tap water just as with the initial rinse. Keep going until you are certain the last of the soap has gone down the drain. You could actually stop here, but in most places tap water has enough minerals in it to cause spotting when it dries. That's where the distilled water comes in and is why you MUST use distilled, not bottled, water. Use plenty of distilled water, maybe even the whole gallon; you want to be sure you rinse away any minerals or salts from the tap water bath. When you are done, it's time to dry.

I sometimes prop the mirror up on a counter to dry, but usually I leave it in the sink (after I've replaced the towel padding with a dry towel). The sink is probably safest. You don't want the mirror to fall over, and in the sink it will be out of the way of folks who might cause grief—like kids or cats. The mirror will dry quickly in most climates if it's at an angle steep enough that water tends to slide off its surface. In our humidity, I usually give it a little help, wicking the big drops off its surface with the corner of a paper towel—without touching the mirror's surface, of course.

While waiting for the mirror to dry, clean/dust the interior of the mirror box and perform other adjustments or housekeeping as required. When the primary is water-drop free, carefully move your pride and joy from sink to scope, place mirror in cell, fasten everything down as 'twas before, and check the collimation. Tweak that and you are done. Thank god.

And that is it. Fun is fun, but done is done. Cleaning a mirror is not hard and it is not scary. I go out of my way to underline the caveats because some folks just can't leave well enough alone or keep from going too far with optical cleaning. You would have to hear him tell it to get the full effect, but my old friend Doc Clay Sherrod tells the story of a dude with a brand new LX-200 who notices a speck of dust on the mirror. The denouement is that the scope winds up under water in the bathtub. I know none of y'all would let the great god Murphy lead you so far astray, but I still want to be on record, when it comes to optical cleaning, as saying TAKE IT EASY ON YOUR BEAUTIFUL MIRROR.

Other than that, muchachos, all that remains for me to say this time is Happy New Year 2013. Hope you have a good one. Unk and Miss Dorothy? I believe it is going to be a great one, if a year that will ring in some changes 'round the Old Manse. Stay tuned.

Next Time:  More CRAZY computers...


Comments:
Happy New Year! Thank you for the great stories, and please keep doing so!
 
Always enjoy your blog. One question... Let's say you do mess up and scratch something. Can it all be fixed with a re-coating?
 
It will take many, many scratches before performance will be affected. If the scratch is not so deep that it goes into the mirror's glass, yes, recoating will fix it.
 
Happy New Year! And thanks for all the astro insight and comic relief you provide here and elsewhere. Two questions (1) Where do use the paper towel you mention? Some of the pictures above actually looks like you dabbing water off the mirror with a piece. (2) does the collimating washer shaped dot on the mirror tend to move or come loose, and then what? Thanks from a fellow Navy civilian (a Rickover guy) and NOVAC member (hope to see you at the AHSP this year).
 
Hi Jim:

I use the corner of a paper towel to "wick" droplets off the surface of the drying mirror without touching the paper towel to its surface...

I use a self-adhesive paper reinforcer. If it comes loose, just replace it. Don't know the exact center? Cut a circle of paper the size of your mirror, fold into quarters, put a hole through the center of the "crosshairs" that will form from the folds, and mark with a soft pencil or water based marker. ;-)
 
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