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tag1260
scholastic sledgehammer
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Reged: 10/07/12

Loc: Ohio, USA
Mirror opinions
      #5528859 - 11/19/12 09:33 PM Attachment (16 downloads)

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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frito
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Reged: 10/05/12

Loc: Fremont, CA
Re: Mirror opinions new [Re: tag1260]
      #5528868 - 11/19/12 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.

Edited by frito (11/19/12 09:37 PM)


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frito
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Reged: 10/05/12

Loc: Fremont, CA
Re: Mirror opinions new [Re: tag1260]
      #5528869 - 11/19/12 09:36 PM

dup post

Edited by frito (11/19/12 09:37 PM)


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SeattleScott
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Reged: 10/14/11

Re: Mirror opinions new [Re: frito]
      #5528994 - 11/19/12 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.


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GOLGO13
Carpal Tunnel


Reged: 11/05/05

Loc: St. Louis area
Re: Mirror opinions new [Re: tag1260]
      #5529019 - 11/19/12 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.


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Phil Sherman
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Reged: 12/07/10

Loc: Cleveland, Ohio
Re: Mirror opinions new [Re: GOLGO13]
      #5529122 - 11/19/12 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


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killdabuddha
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Reged: 08/26/11

Re: Mirror opinions new [Re: GOLGO13]
      #5529126 - 11/19/12 11:36 PM Attachment (19 downloads)

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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Bill Weir
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Loc: Metchosin (Victoria), Canada
Re: Mirror opinions new [Re: killdabuddha]
      #5529257 - 11/20/12 01:08 AM

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

Bill


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tag1260
scholastic sledgehammer
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Reged: 10/07/12

Loc: Ohio, USA
Re: Mirror opinions new [Re: Bill Weir]
      #5529654 - 11/20/12 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?


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GOLGO13
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Reged: 11/05/05

Loc: St. Louis area
Re: Mirror opinions new [Re: tag1260]
      #5529671 - 11/20/12 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.

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tag1260
scholastic sledgehammer
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Reged: 10/07/12

Loc: Ohio, USA
Re: Mirror opinions new [Re: GOLGO13]
      #5529686 - 11/20/12 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.

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Dave74
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Reged: 10/23/12

Loc: Gelatinous, MA
Re: Mirror opinions new [Re: tag1260]
      #5529690 - 11/20/12 09:47 AM

Have you looked at the sky with it?

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tag1260
scholastic sledgehammer
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Reged: 10/07/12

Loc: Ohio, USA
Re: Mirror opinions new [Re: Dave74]
      #5529694 - 11/20/12 09:49 AM

Yes I have.

http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/5527000/page...

Edited by tag1260 (11/20/12 09:49 AM)


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GOLGO13
Carpal Tunnel


Reged: 11/05/05

Loc: St. Louis area
Re: Mirror opinions new [Re: tag1260]
      #5529702 - 11/20/12 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

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Dave74
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Reged: 10/23/12

Loc: Gelatinous, MA
Re: Mirror opinions new [Re: tag1260]
      #5529709 - 11/20/12 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.

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dpwoos
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Re: Mirror opinions new [Re: tag1260]
      #5529719 - 11/20/12 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.


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csrlice12
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Reged: 05/22/12

Loc: Denver, CO
Re: Mirror opinions new [Re: dpwoos]
      #5529729 - 11/20/12 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?

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tag1260
scholastic sledgehammer
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Reged: 10/07/12

Loc: Ohio, USA
Re: Mirror opinions new [Re: csrlice12]
      #5529746 - 11/20/12 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.


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Bill Weir
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Loc: Metchosin (Victoria), Canada
Re: Mirror opinions new [Re: tag1260]
      #5529893 - 11/20/12 11:27 AM

Quote:


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


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tag1260
scholastic sledgehammer
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Reged: 10/07/12

Loc: Ohio, USA
Re: Mirror opinions new [Re: Bill Weir]
      #5529918 - 11/20/12 11:36 AM

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

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