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CESDewar
GorillAstronomer
Reged: 01/16/05
Posts: 2069
Loc: Morganton, GA, USA
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I have a pair of 8x42 Celestron Regal LX's which I purchsed used some time ago (so no warranty service available). There's a really noticeable flaw in the coating on one objective - enough to cause very obvious flaring when observing a bright object like the Moon or Jupiter. it's a small rectangular region about 2x3mm and I was quite surprised at what a difference it made to have lost the coating in that small area.
Is it even feasible to recoat an objective? Or is this just a flaw that will relegate these binoculars for limited use or a firesale?
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ronharper
Pooh-Bah
Reged: 02/14/06
Posts: 1276
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CES,
You can find coating services on the web, but the problem with a job like that is getting the old coating off. The whole surface has to be coated, you can't just put the coating in one desired spot. It has to be abraded, which ruins the smooth surface and optical finish of the surface. Unlike with metallic reflective coatings, there is no chemical process to remove the glasslike antireflective coating without eating the glass too. It is almost never worth the trouble of custom-refiguring the surface. This would surely cost more than the worth of the binocular.
You might try to mask off the spot with a bit of opaque tape. The resulting diffraction effect might or might not be less disturbing than what you are seeing.
Ron
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Mark9473
Post Laureate
Reged: 07/21/05
Posts: 3211
Loc: 51°N 4°E
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If the coating is lost on the outward-facing side of the objective lens, isn't all that's supposed to happen that a bit more light get's reflected back toward the source? How does this result in flaring?
Probably a silly question, but I'm curious nonetheless.
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Mark
Leica 8x20; Vixen 8x42; Swift 8.5x44, 10x50 and 20x80; TS 7x50; Orion 15x63; Docter 15x60
WO Megrez II 80 FD + Baader 90° T2 Amici
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CESDewar
GorillAstronomer
Reged: 01/16/05
Posts: 2069
Loc: Morganton, GA, USA
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Quote:
You might try to mask off the spot with a bit of opaque tape.
Yes, I had thought about that, but I was also wondering if there was something that I could "paint" onto the surface that might be less obstructive than trying to put a dot with a magic marker or use some opaque tape.
What exactly is the coating that they put on the objective made of? Don't think I've read anywhere exactly what "coatings" are....
As for the question about why it would cause flaring - it is on the outside objective, but it's very definitely the cause of the flaring as I did try putting some tape over it (which removed the flaring, but caused an observable anomaly in the view - perhaps because it was too big).
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ronharper
Pooh-Bah
Reged: 02/14/06
Posts: 1276
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CES,
Here is a description that leans a little bit towards nerd territory, but how else can you say it?
The glassy substances like MgFl2 are good because they are close enough to the ideal index of refraction to do a lot a reflection suppression, rugged, and easily evaporated in a vacuum chamber.
There is nothing you could paint on there that would even come close to the required 130nm thickness in the right refractive index, it is unfortunately just way past "old world craftmanship".
I'm with Mark though, in that I don't get it how a small missing spot of coating could make such a noticeable effect. So, since we're sort of in lala land anyhow, who knows? Clear nail polish?
Ron
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DJB
Carpal Tunnel
Reged: 02/23/05
Posts: 1589
Loc: Lisle NY
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Hi all,
Yes, I would just ignore the small spot--one probably could not see a before or after test effect.
Older coatings, circa 1960s, were usually made up of one to three coatings.
The modern coatings can consist of 11+ (16 I'm sure of) layers of very special and very thin, but controlled, applications of various elements. These are known to only the mfgs., who will never reveal their processes.
Again, not to worry about a small aberration, unless you wish to make it perfect and view the objective's surface rather than observing the sky. Just teasing here.
Best regards,
Dave.
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KennyJ
Reged: 04/27/03
Posts: 12901
Loc: Lancashire UK
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I'm not sure what differences in substances , application techniques or relative levels of secrecy are involved , but I've spent one day every year for the past eleven years carrying out essential safety work in a factory where anti - scratch , anti - glare and tinted coatings are applied to eye - glass lenses , before them being sent elsewhere , at some stage during the transportation of which , the products somehow magically undergo a change of name to become products with " established household name respectability ".
During every visit , several moments spent sneakily glancing sideways at white coated personnel and the processes taking place have not revealed much I would consider to be worthy of the classification " rocket science " or " top secret " .
A few times I've quietly asked various operatives about the process involved , but apart from one of them ( about five years ago ) none of them have seemed particularly knowledgable or interested in what they are doing or why , it is just a ( very routine , very repetitive , very boring , poorly paid ) job to them .
Indeed , every year when I go there I see a new team of operatives working in those areas and there seems to be a distinct shift in more recent years toward non - English speaking operatives ( perhaps these employees have been chosen for being less likely to share the trade secrets with visitors such as myself ? ) .
I get the impression it is the kind of " specialised " job that could be taught to anyone with a modicum of intelligence and practical ability , within a few minutes .
Kenny
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If everyone is thinking the same thing , no-one is thinking - General George S.Patton
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milt
professor emeritus
Reged: 09/13/04
Posts: 555
Loc: Arizona
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Quote:
isn't all that's supposed to happen that a bit more light get's reflected back toward the source? How does this result in flaring? Probably a silly question, but I'm curious nonetheless.
Not a silly question - I wouldn't have said this resulted in flaring either.
Here is a recent Roland Christen post on the difficulty of coating removal:
http://tech.groups.yahoo.com/group/ap-ug/message/46101
I would just live with it.
Milt
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GlennLeDrew
Pooh-Bah
Reged: 06/18/08
Posts: 1275
Loc: Ottawa, Ontario, Canada
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When I aspherized my 50mm bino objectives, the coatings on the worked, front surfaces naturally got polished away. It took about 10 to maybe 15 minutes to totally disappear. The *very slight* loss of light is absolutely not missed.
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Home-made 11X50 right angle bino, 8.1 deg. FOV
Modified 26X100 bino, 3.5 deg. FOV
Home-made Mk II RA bino, using interchangeable objectives and eyepieces
My Gallery
Mediocre minds discuss people. Good minds discuss events. Great minds discuss ideas.
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DJB
Carpal Tunnel
Reged: 02/23/05
Posts: 1589
Loc: Lisle NY
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Hey Kenny,
Thanks for that great input.
I, too, understand that the "techies" probably do not completely understand exactly why they are doing what they HAVE to do!
Somewhere, sometime, the optical people had to have developed all coatings in the lab and then released the specs and procs. to the coating facility. Thanks.
Best regards,
Dave.
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