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#1 tag1260

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Posted 19 November 2012 - 09:33 PM

I am thinking the mirror in my newly acquired 12" dob may need re-coated. Anyone able to tell from this pic if it shows degradation? It looks really dusty and although I know a light down the tube isn't a good indication, I've had it out and it looks worse than this picture shows. It looks as though the previous owner my have tried to clean it, as there are what looks to be swirl marks like someone would use to clean a window. The grainy look in the pic isn't just the pic but the way the mirror looks.

Thanks

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#2 frito

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Posted 19 November 2012 - 09:36 PM

doesn't look great but i can see the camera flash in that photo. take the mirror cell out and take a photo of its reflected image without a flash lighting up the surface.

otherwise i'd say take it out and see how it performs. a really dirty mirror will degrade the amount of light it can see but otherwise will impact very little in how it works.

#3 frito

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Posted 19 November 2012 - 09:36 PM

dup post

#4 SeattleScott

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Posted 19 November 2012 - 10:34 PM

Could always clean it to get that dust off and see what it looks like after that. If you leave the dust on there it can degrade the mirror coatings faster. (Of course overcleaning will degrade coatings too so there is a balance.)

I looked through an 8" SCT with a visibly oxidized mirror many times and it was surprising how well it performed, other than the Ring not having a ring shape.

#5 GOLGO13

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Posted 19 November 2012 - 10:43 PM

Looks to me like it needs recoating. Suggest either searching for some threads in the reflector forum on re-coating dealers (I remember one a few months ago)...or ask again.

You certainly could clean it since it's not going to hurt much more, but I see spots on there that look like the mirror is chipping off.

#6 Phil Sherman

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Posted 19 November 2012 - 11:33 PM

Your mirror looks to be in good shape when compared to one I "fixed" for a friend. His was so bad that there was little reflected in it because it was covered with mold because it had been poorly stored for well over 25 years. After a good cleaning, there was a single bad spot left in the coating, around 6mm in diameter.

I'd read up on mirror cleaning techniques and take a stab at it before sending it out for recoating. Another question to be answered before recoating is the quality of the mirror's figuring. As already recommended, try it out before doing anything. A star test under decent seeing conditions will give you lots of information about the quality of the mirror.

Phil

#7 killdabuddha

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Posted 19 November 2012 - 11:36 PM

Are you sure that isn't the character for "joy?" The maker woulda signed it that way from the outside in, so you gotta look at it upside down. Before you recoat, what's the harm in a re-figure? Everyone does it.

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#8 Bill Weir

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Posted 20 November 2012 - 01:08 AM

Do this http://www.youtube.c...h?v=9Y8xFnXFVGQ then report back.

Bill

#9 tag1260

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Posted 20 November 2012 - 09:29 AM

Thanks for all the replies. I tried cleaning it last night and it looks the same. Doesn't appear to have taken anything off. Someone above mentioned it looked as though there was chips of coating missing. That's just the picture as the coating looks complete but just as though it has dust "imbedded"" for lack of a better description. By the way, this is an Antares 12" which is a GSO scope. So I don't think there is a maker's mark on the mirror.

What does re-figured mean and what would something like that cost for a 12" mirror? And who does this? I've already gotten pricing on re-coating and it doesn't seem unreasonable at all but is there anything I should know before sending it off?

#10 GOLGO13

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Posted 20 November 2012 - 09:36 AM

I wonder if there are more agressive cleaning methods for a situation like this. What cleaning method did you use? I had to be a little more forceful with my mirror lately...also had gunk that didn't come off easy.

#11 tag1260

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Posted 20 November 2012 - 09:45 AM

I just did the dish soap and sterile cotton drag method. I looked around the net and see a method doing the same but with acetone. Didn't try it as I don't know if it "could" damage the coating more than it already may be. Tried to get a better picture of the mirror but that just doesn't seem to be possible for some reason. The coating just looks dull and full of dust. When I shine a light from behind, I do have a couple pinholes but nothing to be concerned about there, I don't think.

#12 Dave74

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Posted 20 November 2012 - 09:47 AM

Have you looked at the sky with it?

#13 tag1260

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Posted 20 November 2012 - 09:49 AM

Yes I have.

http://www.cloudynig...5527000/page...

#14 GOLGO13

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Posted 20 November 2012 - 09:52 AM

At think point I'd say before you send it in try one of the more agressive methods of cleaning...and if that doesn't work the recoating will :)

#15 Dave74

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Posted 20 November 2012 - 09:56 AM

Oh. Sorry I missed it. I guess it's a matter of if it's worth being re-coated, right? If you're getting good views through it now, maybe the re-coating won't improve that all that much. And it won't be worth it if it ends up costing more than what you paid for the scope. But if it's relatively cheap, go for it. I'm interested to hear how much it costs.

#16 dpwoos

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Posted 20 November 2012 - 10:01 AM

Are you unhappy with how the scope is performing? If so, you should post your specific issues. If not, then why do you care what the mirror looks like? It is likely that you are overreacting. Not to say that it is impossible that the mirror needs recoating, but rather that it isn't likely.

I suggest that you visit your local astro club, where you will be able to compare what you have to what others have. As an example, my 10" mirror looks pretty dirty and yet I get absolutely fantastic views.

#17 csrlice12

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Posted 20 November 2012 - 10:09 AM

Dave brought up a good question. What is the average cost of having a mirror recoated, and, is there a listing of businesses that do this. Also, can the commercial mirror be reconfigured (improved) and what is the average cost of that?

#18 tag1260

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Posted 20 November 2012 - 10:17 AM

I got prices on a 12" from various websites of between $100 to $200 depending on the coater and the coating used. Add about $60 to that for shipping both ways ($30 each way w/ insurance by USPS.)

Now I don't see a cost to re-figure a mirror anywhere.

#19 Bill Weir

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Posted 20 November 2012 - 11:27 AM

Now I don't see a cost to re-figure a mirror anywhere.


Because that will be dependant on how much work the person doing the refiguring has to do. This is also not taking into account of what that person charges for their time. Different glass pushers have different prices. You will need to actually contact them and they won't be able to give you a real price until they see/test the mirror.

Bill

#20 tag1260

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Posted 20 November 2012 - 11:36 AM

OK. I'm kinda dumb on this stuff. What exactly is figuring?

#21 killdabuddha

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Posted 20 November 2012 - 12:29 PM

Dear tag,

Didn't mean to concern you at all. It's just that folks often come into mirrors--even new--without knowin their quality. And since yer sendin it in for a re-coat, they'll test the actual mirror surface for you for its smoothness and the accuracy of its parabola (the final polishing that gives our mirrors their shape and let's them do what they do so well). Re-figuring can be very affordable and add real performance, and is often only a 30-minute job and so mite be worthwhile. Sometimes it's even necessary when the original aluminum won't strip properly. Have a look here

http://www.swayzeopt...e/refigure.html

Whatever the case, when you send it to be re-coated they'll test and advise whether a re-figure is worth it, and you can proceed from there. Sorry for any anxiety I may have produced, but a 12" mirror is a good size and I'd want such to be performin optimally where possible.

And yes, of course, be lookin thru it now before you send it off. Not that you'll necessarily know that it's what you want performance-wise, but so that you can appreciate the difference before and after, cuz I think yer determined to get it re-coated anyway, which is oh so natural and what we would do, too.

#22 Jon Isaacs

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Posted 20 November 2012 - 12:32 PM

Are you unhappy with how the scope is performing? If so, you should post your specific issues. If not, then why do you care what the mirror looks like? It is likely that you are overreacting. Not to say that it is impossible that the mirror needs recoating, but rather that it isn't likely.

I suggest that you visit your local astro club, where you will be able to compare what you have to what others have. As an example, my 10" mirror looks pretty dirty and yet I get absolutely fantastic views.


:waytogo:

Jon

#23 csrlice12

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Posted 20 November 2012 - 12:34 PM

Making sure that the mirror is smooth (no groves, or rippled surface) and within the tolerence level for that particular mirror size/shape (this will vary depending on the mirrors size and shape, parabolic/spherical). Most commercial mirrors can be "reconfigured", that is, the mirror blank can be "reground" (actually, its more like tweeking/fine tuning).

#24 frito

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Posted 20 November 2012 - 01:07 PM

i'd keep looking for someone who does coating cheaper. there is a local guy in the SF Bay area that only charges 60 dollars to coat 10" mirrors. he does not however have the capability yet to do larger than that unfortunately. in the mean time from the sounds of your first light thread the views are still good in the scope so try to forget what you have seen and get out and put the thing to use :)

#25 uniondrone

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Posted 20 November 2012 - 01:39 PM

i'd keep looking for someone who does coating cheaper. there is a local guy in the SF Bay area that only charges 60 dollars to coat 10" mirrors. he does not however have the capability yet to do larger than that unfortunately. in the mean time from the sounds of your first light thread the views are still good in the scope so try to forget what you have seen and get out and put the thing to use :)


Optical Wave Labs is running a sale: half off of all standard and enhanced coatings. Basically it's $48 for a 12" mirror, plus $15 for stripping the old coatings, plus S&H charges. That's a pretty great deal.

Check it out here: link






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