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Old 27-07-2021, 07:18 PM
Cellmend (Justin)
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Re coat Mirrors or just replace?

Hi Guys,
I’ve inherited a Meade 10” Lightbridge and both mirror surfaces are shot! Is it still an option to re coat these mirrors cost effectively or just replace them?
Any advice appreciated.
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Old 28-07-2021, 03:16 AM
astro744
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You need to do an optical test at least on the primary, (either Foucault, Ronchi, Star or all three). Requires minimal equipment but some knowledge on how to interpret.

The advantage of re-coating is that the focal length of your mirror will remain exactly as it was which isn’t guaranteed if you buy a new one although there could only be mm in it. If your tests indicate you have a good optical surface then re-coat since you won’t be entirely certain what the optical surface accuracy of your new mirror is until you test it.

If it was a custom mirror made by a reputable optician, then re-coat for sure. Given that it is a mass produced mirror you could buy new and get something of equal or better or worse quality, (I’m talking optical quality without the blemishes). These days mass produced mirrors are very good but quality control is not so good but that is the price you pay (or not pay) to get a larger cheap mirror.

I have a Meade 16” f4.5 Lightbridge that I am very happy with. I too have a 10.1” f6.4 custom figured Newtonian by a master optician that simply excels in good seeing giving pin point star images. The 16” pulls in a lot more galaxies simply due to the aperture which is what I enjoy most about it. I also have a 10” f4.7 Skywatcher which I bought the kids used. It is a fun ‘scope that provides pleasing views of all types objects in the night sky.

If re-coating the primary get the secondary done at he same time, (should be minimal extra cost), or buy another cheap (GSO) secondary or expensive (Antares) secondary, choice is yours. I wouldn’t glue an expensive secondary, rather get a proper holder with a lip. I’d stick with the Meade secondary too and get it re-coated although having never to deal with a glued secondary I’m not sure on the pros and cons of removing them from their glued holder.

I got my 10.1” f6.4 and 6” f5.5 and 1.83” secondary re-coated in 2003. Still look like the day I brought them home. Also bought a 2.14” secondary from the guy doing the coating that day. No longer in business so I’m not sure where the best spot to get it done these days but I’m sure someone else will chime in.

If you buy new then keep your old mirrors (pri/sec) until you’ve fully tested your new ones. If you’re happy with them then off load your old ones as there’s always a buyer out there, or get them re-costed at a later date and keep them with the Lightbridge as a set. Note if buying new the focal length will have to be a close match otherwise the focal plane won’t be where it should be and some simple or not so simple tweaking may be required.
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Old 28-07-2021, 07:01 AM
glend (Glen)
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I will disagree with the previous post. You can actually buy much higher quality primary mirrors off the shelf now, than your old one. There are many sources for GSO Primaries, both locally and from Agena Astro, which have very high spec production quality.
I used a GSO 10" primary in the carbon strut reflector I built several years ago, it produced amazing images.
If you could find a local recoatung business, the last one closed a while back, it will cost you likely minimum of $500 plus shipping to recoat your old mirror. And you will be no better off, quality wise, than whatever figure was put on the old Lightbridge.
Shop around is my advice. Even if you have to adjust the primary or secondary slightly, a higher quality mirror will be worth it, imho.
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Old 28-07-2021, 09:39 AM
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Rainmaker (Matt)
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Recoating can be done by Wayne Sainty at Palmway Optical, Forster/Tuncurry area. 10" Primary is about $380 Standard or $435 for Enhanced.

Easy drive from Newcastle... superb job, I had my 18" done 2 years ago, dropped it off on my way to Brisbane, picked it up the next day on my way back....

BUT.... do you know if the mirror is actually any good as far as its figure??
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Old 28-07-2021, 11:20 AM
astro744
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Quote:
Originally Posted by glend View Post
I will disagree with the previous post. You can actually buy much higher quality primary mirrors off the shelf now, than your old one. There are many sources for GSO Primaries, both locally and from Agena Astro, which have very high spec production quality.
I used a GSO 10" primary in the carbon strut reflector I built several years ago, it produced amazing images.
If you could find a local recoatung business, the last one closed a while back, it will cost you likely minimum of $500 plus shipping to recoat your old mirror. And you will be no better off, quality wise, than whatever figure was put on the old Lightbridge.
Shop around is my advice. Even if you have to adjust the primary or secondary slightly, a higher quality mirror will be worth it, imho.
How do you know the quality of the old one? I suggested testing before deciding otherwise you really don't know the quality of the mirror you may discard.
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Old 28-07-2021, 01:10 PM
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mura_gadi (Steve)
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Hello,

I think I read somewhere that some of the lightbridge series used GSO mirrors for a while. I see you have some writing on the side of the mirror, can you read any of it?

You can get a F5 250mm from a GSO mirror supplier that would suit your scope perfectly. You can get a new primary and secondary for around $380(plus postage). As long as the are "diffraction limited" as sold by GSO you'll be fine.


Steve
Ps. The current surface needs to be removed prior to a recoat, and that is not always successful. I'd be worried that the mirror maybe be too far gone for a recoat. A mirror surface should be down to single digit microns when polished and ready for coating.

Last edited by mura_gadi; 28-07-2021 at 01:34 PM.
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Old 28-07-2021, 02:03 PM
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multiweb (Marc)
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Quote:
Originally Posted by Cellmend View Post
Hi Guys,
I’ve inherited a Meade 10” Lightbridge and both mirror surfaces are shot! Is it still an option to re coat these mirrors cost effectively or just replace them?
Any advice appreciated.
If the glass surface is not chipped or pitted you could get them recoated by Sainty. If you want to get them tested they'd have to be stripped of coatings first anyway.
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Old 01-08-2021, 10:20 AM
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xelasnave
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Is it worth the effort given absolute bargains present here regularly ..units that often have goodies that will save you money.
Alex
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Old 01-08-2021, 03:04 PM
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Merlin66 (Ken)
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A quick test of the mirror can be done at home.
If you don’t go ahead with recoating or replacement, you can strip the old coatings and use the scope as a white light solar scope.
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