Can you keep a mirror set in the loft for 40 years then use it in a home made OTA?

[DannyLee]

Hi All,

around 1978 I bought a ten inch mirror set from Fullerscopes. It was  'B' quality mirror 1/8th wave claimed I think. I used it in a home made wooden tube that looked like a wardrobe, and had the neighbours laughing cos they thought I was burying the wife when I dragged it out at night!. The stand was knocked up out of 2'' screwed steel pipe, bit Dobsonian really as the movement was on the screw threads. Ok so it was crude, but for visuals it was great and remarkably rigid and smooth. Then we moved, and then family, and then jobs, and then.... short story, The wardrobe was burned and the mirrors put into the loft in a box. they followed me for 5 houses, but stayed in the box.

Over the last ten years I have messed around with astronomy, bought a 127 Mak goto but that is now on an EQ3 , I thought the goto was rubbish, not that it didnt work, but why would you bother?

Recently I bought off members of this forum a SW 200p thanks, its great. and a SW HEQ5 which is also great, thanks Ben, so I decided to resurrect my mirror set, but it had been in several lofts for 40 years...and I didnt have a tube.

so I made a skeleton tube out of 15mm copper pipe with soldered fittings and made a mirror cell out of three bits of ally plate I had lying around, I tig welded them and fitted them to the tube, along with a home made spider (steel and ally) and fitted them with a 2'' focusser I bought ages ago. The idea was a crude tube which I could attach to the HEQ5 to allow me to do star tests on the 40 year old mirror set to see if it was worth using again. When I got it out it was filthy with marks that looked suspiciously like ally oxide. So I washed it in warm soapy water and rinsed in de-ionised water. The result is great no oxide marls just some old sleeks caused no doubt by my clumsy handling 40 years ago.

See the piccies below, any comment or suggestions much appreciated. BTW, its difficult photographing the muck on a mirror surface...

 

 

[andrew s]

Much older mirrors are still in active use. It might need a re-coat to reach it's full potential. Long term the copper tube might creep out of alignment. Steel would be better.

Regards Andrew

[skybadger]

Really clever use of copper tube. Bit soft but good for testing. 

I have older mirrors than that in telescopes so no worries there. 

Mike

 

[oobydooby]

If you decide to go with a steel frame, you could always use the copper one as a runner bean frame.

Seriously though, wrapping the whole thing with a black sheet might keep out detritus and stray light, and would not add too much weight.

[DannyLee]

2 hours ago, oobydooby said:

If you decide to go with a steel frame, you could always use the copper one as a runner bean frame.

Seriously though, wrapping the whole thing with a black sheet might keep out detritus and stray light, and would not add too much weight.

 

Thanks for the comments guys,

My wife already has mentioned its potential for training sweet peas, no seriously, she has...

If I think the mirrors are worth the effort after star test, I will fabricate the next OTA out of 20mm aluminium tube, all welded connections, and I will be a lot more careful over maintaining the hexagon shape whilst putting together, the copper one is a bit, well, slightly off perfect shall we say.

I also intend to make a fork mount for it , possibly to swap the Dec shaft on the HEQ5 for a fabricated ally fork, removes the need for counterweights, so should increase the stand capacity a bit.  BTW the copper OTA with mirrors weighs 14KG so I think a heavier ally one might add a couple of grams...

I will post more piccies if I go ahead with it

Dan

 

[Dude_with_the_tube]

personal opinion is that age of optics isnt that important.Sometimes those old mirrors or lens`s are far better quality then modern equivalents.Mirrors can be re-coated if needed and even reconfigured.Refractor lens can be dismantled,cleaned, re coated,but lens coatings should last a life time.

At the moment I have 2 fracs at home both are well over 20 years old and there is nothing needed to be done on both.One was recolimated 5 years ago,other just recently.I am sure quite a few folks here have even older instruments at they possession and some of them are 50 and some also 70+ years old and still going strong.

[DannyLee]

Actually, what really surprised me was the condition of the ally coating after I washed it. Hardly a blemish, few light sleeks around the edges but nothing else, after 40 years. Admittedly it was covered that whole time, but I sort of assumed the ally would eventually corrode anyway. Doesnt seem to have done though.

Hoping to get the glass into the tube for a star test next time the clouds stay at home, will update then.

Dan

[Peter Drew]

A and B quality mirrors used by Fullerscopes of that period were usually supplied by David Hinds. B quality usually referred to the glass used or a couple of minor cosmetic issues rather than any reduction in the 1/8 wave figuring accuracy. The longevity of their coatings is legendary.  

[DannyLee]

11 hours ago, Peter Drew said:

A and B quality mirrors used by Fullerscopes of that period were usually supplied by David Hinds. B quality usually referred to the glass used or a couple of minor cosmetic issues rather than any reduction in the 1/8 wave figuring accuracy. The longevity of their coatings is legendary.  

Hi Peter, 

I clearly remember debating whether to get an 'A' 8 inch or a 'B' 10 inch. As ever, size was more important ( I was young and such...) if I remember correctly the price was just about the same, there was a substantial diff in cost between A & B for the same size.   One thing I do not remember clearly is whether my mirror was 'Inconel coated'  or not. Fullerscopes ads made much of that at the time but that was also at additional cost. Maybe thats why my coating has survived?   

Regards

Dan