5 replies to this topic

[Houdini]

After 13 years, it is time to give the large mirror of my 1100 mm (43") telescope a new coating. The mirror still has its original coating from 2012, and it is now in very poor condition.

 

After a long search and with the help of friends on the French Astroforum, I found a European company capable of processing such a large diameter at a reasonable price: Zaot, based in Milan, Italy.

 

Today, I removed the mirror from the telescope, which was quite an undertaking. The mirror has a diameter of 1103 mm and a thickness of 59 mm. It weighs just over 100 kg. To handle the mirror safely, I used a workshop crane that was purchased specifically for this telescope.

Below are a few pictures of the process.

 

This weekend, I will transport the mirror to Milan in my van so that Zaot can start working on it Monday morning.
If all goes well, the mirror will be back next Saturday.

 

Fingers crossed!

Robert

 

 

 

 

 

 

Edited by Houdini, 13 June 2025 - 08:11 AM.

[petert913]

WOW ! 

[Astrojensen]

Oh, that's good to know. A friend and I have a 25", that might need recoating in the not too distant future.

 

 

Clear skies!

Thomas, Denmark

[sixela]

25", that still works a little closer to home (at MCM Optique in France, East of Paris). 30" they can do, but not 1100 mm...

[IslandPink]

Great !

I just went to your website and had a look around. Very interesting.

[Houdini]

Friday I picked up the mirror with the new coating at Zaot in Milan, and on Saturday I drove the 1000 km back from Milan to the Pyrenees.
The mirror looks as good as new!

 

 

 

Compare with the last picture of the starting message of this thread to see the difference.

 

Zaot attaches a piece of test glass to the mirror in the vacuum chamber to measure the reflectivity, and you get a graph with the measured values.
I had chosen their SAP EHV (aluminum + quartz protection multilayer) coating which was advertised as 92% to 94% reflectivity.

 

The measurement of the test glass gave 95% reflectivity in blue, 94% in green and decreasing to 90% in red.
In the band of human night vision (about 450 to 550 nm) it's between 93% and 95%.

Edited by Houdini, 23 June 2025 - 01:58 AM.