1930's Scope refurb update..

[marcopolo]

Just a few updates  on what i'm doing with the 1930 scope to get it functioning. Its a 7.6in F8.9 reflector on a VERY heavy GEM mount.

Mirror coating and 'testing' by Orion:     http://marcosatm.com/2016/03/05/mirror-mirror-hows-your-figure/

Building a Foucault tester (head made from LEGO!!) and verifying Orion Optics results: http://marcosatm.com/2016/03/14/chasing-doughnuts/

Stripping down and rebuilding the EQ mount: http://marcosatm.com/2016/02/11/strip-and-show-me-what-youve-got/

 

[unromeo21]

Except that glass DOES NOT FLOW over time. You have to accept that. It was just over corrected from the very beginning... 

[Dave Lloyd]

On 18/03/2016 at 14:06, unromeo21 said:

Except that glass DOES NOT FLOW over time. You have to accept that. It was just over corrected from the very beginning... 

Hmm I think it does. It's a supercooled fluid. That's why some Tudor window panes are ever so slightly thicker on the bottom edge. I agree though I don't think it'll make a difference over 80 odd years.

[Dave Lloyd]

15 minutes ago, Dave Lloyd said:

Hmm I think it does. It's a supercooled fluid. That's why some Tudor window panes are ever so slightly thicker on the bottom edge. I agree though I don't think it'll make a difference over 80 odd years.

Oh no it doesn't though. I've just read that's a myth that's been disproved. Apologies.

[billyharris72]

Pretty sure it does flow though... my understanding is that most minerals do.

Take another look at that objective in two or three hundred million years and I guarantee there will be some (perhaps not readily perceptible) change!

Hey, turns out this is also wrong - solids move but not like liquids at all. Multiple retractions in the same thread! 

[Peter Drew]

Thinnish glass coffee table tops have been known to sag over a period of time. 

[Ruud]

 

 

[Dave In Vermont]

My training in chemistry has shown me that 'glass' is a liquid with a very high boiling-point. Hence the artistry of glassblowers. Such as in Venice, Italia where they make some incredible works from glass. And the windows of old houses can look blurry in old age. But this takes a very long time indeed.

Dave

[unromeo21]

yep, we now have such a huge source of information on our hands now (the internet). It's time we do some research before believing in old myths like these. Scientists estimate that it might take billions of years to even notice any microscopical change in a glass piece due to flow at room temperature. 

[marcopolo]

Very interesting discussion guys; it's all good information. It could have indeed been overcorrected from the beginning. Surprising given the mirror maker authored a book on preparation of mirrors for astronomical telescopes!

There is one more piece of info that may be important that I forgot to mention. The mirror was wedged in VERY tight to the outside of the cell with brass strips - could this over the 80 years have 'pinched' the mirror and therefore permanently imparted the overcorrection?

Anyway I guess the important part now is to remove that overcorrection so the scope performs well.......