Mirror resurfacing

Holomark · Post by **Holomark** » Mon Nov 19, 2012 7:47 pm

I am getting ready to hand over my 12 inch collimating mirror to someone to resurface. It was an e-bay purchase. It was not perfect when purchased and in my care has only gotten worse. I found one person in the area who seems to know about resurfacing and who has quoted a very reasonable price.

I don't know much about resurfacing and was wondering if there is anything special about the resurfacing of a collimating mirror for holography that I need to make sure is done or ask about.

So, anything I sould know?

Thanks
Mark

BobH · Post by **BobH** » Tue Nov 20, 2012 11:47 am

Why would it need resurfacing? Do you mean re-coating? Re-coating is just stripping the old one and putting on a new one in a vacuum chamber. Resurfacing means re-polishing to improve the figure or remove deep scratches or "orange peel". That involves more time and skill. Where are you having it done?

Either way, tell them to NOT put any marks in the center, as is typical for telescope mirrors these days.

holomaker · Post by **holomaker** » Tue Nov 20, 2012 12:03 pm

Yup Bob's got it correct as usual ! It should cost you less than a couple hundred dollars.... be sure to get the "enhanced aluminium coating" usually meaning its got an overcoating to help protect it from the eviroment and your fingers!

Jeffrey Weil · Post by **Jeffrey Weil** » Tue Nov 20, 2012 5:42 pm

Hello Dave,

You've made a slight mistake there. Enhanced alum is an oxide coating to "enhance" reflectivity. All standard aluminum coatings come with silicon monoxide or some other protection to keep it from tarnishing in the air.

I used these guys a few years ago and the mirror still looks great. They did a fine job and it wasn't that expensive either. I got the standard alum coating.

http://www.spectrum-coatings.com/

Jeff W

142laser · Post by **142laser** » Thu Nov 22, 2012 9:04 pm

See if a protected Aluminum is available. This doies not tarnish and holds up better than bare. A couple hundred bucks is reasonable! Phil

holomaker · Post by **holomaker** » Mon Nov 26, 2012 9:06 am

Jeffrey Weil wrote:Hello Dave,

You've made a slight mistake there. Enhanced alum is an oxide coating to "enhance" reflectivity. All standard aluminum coatings come with silicon monoxide or some other protection to keep it from tarnishing in the air.

I used these guys a few years ago and the mirror still looks great. They did a fine job and it wasn't that expensive either. I got the standard alum coating.

http://www.spectrum-coatings.com/

Jeff W

Yes thanks Jeff, i thought that statement might get me in trouble, years back when i had my 12" recoated, the coatings offered were aluminised only (no overcoat), or the "enhanced" version which was topcoated .........

Jeffrey Weil · Post by **Jeffrey Weil** » Tue Nov 27, 2012 12:39 pm

No overcoat! Wow, I don't think I've owned an alum mirror that wasn't protected. How fast do they tarnish?

holomaker · Post by **holomaker** » Tue Nov 27, 2012 1:27 pm

Sorry cant say how fast Jeffery, as i had the "enhanced" version done ............

holorefugee · Post by **holorefugee** » Tue Dec 04, 2012 10:23 pm

Refiguring is another topic entirely and can also be undertaken.

holowizard · Post by **holowizard** » Wed Dec 04, 2013 4:35 pm

If this company does work on telescope mirrors (sounds like they do) you might want to look into protected silver. Aluminum is only 88% reflective; silver gives you table-flat reflectivity at 96% across the entire visible spectrum. Laser light is expensive; every milliwatt NOT absorbed by mirror coatings goes to do more useful work (like illuminating the subject and plate). Short of broadband dielectrics, I would think this is the best way to go (and the cost difference between silver and aluminum, considering the amount of metal actually used, should be minimal).