Re- secondary Mirror

[JohnF]

Anyone imported a Secondary from China for a 10 inch newtonian. My old mirror has lost its coating, and I need to replace, or re-silver it.

Am thinking as it is flat, a surface mirror film, or new mirror from China.

Just purchased a Second hand 10 inch mirror on Gumtree for $40. It is much better than my old one, so no longer thinking about re-silvering it with Silver, "Tollen's test for aldehyd."

My 10 inch mirror was in very poor condition. Covered with dust when I purchased that telescope very cheap, so did not know how bad the Aluminium surface was.

Also thinking about a mylar mirror film onto the old secondary.

[Merlin66]

John,
Forget the Mylar option....not a good idea.
Just find a good secondary from a reputable supplier.

[Saturnine]

You can purchase the appropriate size secondary, 63mm, for the 10' mirror from either Bintel or Andrews Com. for about $50 . Not sure what the surface accuracy of the Chinese secondaries on Ebay or AliExpress is like. They may come from the same supplier to G.S. or Skywatcher and be ok but the price difference is bugger all in the end so buying local is safer.

Have you tried gently washing the secondary, in the recommended methods such as http://www.iceinspace.com.au/63-345-0-0-1-0.html and many other astro websites have similar instructions a well. The coatings on secondaries usually last longer than on primaries as they are facing down and not subject to the same amount of exposure to the elements.

[JohnF]

I did measure my my secondary. It is close enough to 95 X 67 mm. And its coatings are very bad -- gone.

[Saturnine]

The 63mm Secondary that I mentioned previously is the correct size for your primary mirror . Whether the mirror is an Skywatcher of 1200mm f/l or the GSO 1250mm f/l shouldn't matter, the 63mm secondary suits both, unless your tube is oversized for some strange reason.
If you could post some photos of the tube and mirrors and their coating condition it would help. Removing the old secondary from the holder can be a problem as they are usually held on by a silicon glue which is tenacious stuff.

[JohnF]

It may b a home made holder, from white Poly pipe. The mirror, 95 X 67mm was fitted in with a bunch of tissue paper holding it down, so mirror could not move -- was full of ants :D. Poly Pipe was painted black, but not on inside. Holder has a centre adjustment screw, plus has other adjustment from memory. Still trying to work out how to find address of my pictures on my "FORBIDDEN FRUIT" COMPUTER -- Apple light book Air. Have joined the Men's shed as I need to make a Dobson base for it. We have a computer room with a retired Apple Technician, who is going to fix the white line down my screen -- contacts, so I will ask him for help in posting pictures, which I have not bn able to work out.