Pyrex

[slowflow (Barry)]

Hi, I would like to know if the telescopes advertised as having Pyrex mirrors are the same as those with borosilicate glass?
Is there a significant advantage to either?
Thanks in advance..

[bojan]

This is the same thing.
See here:
http://en.wikipedia.org/wiki/Borosilicate_glass
http://en.wikipedia.org/wiki/Pyrex

[Peteren (Peter)]

Originally Posted by bojan

See here:
http://en.wikipedia.org/wiki/Borosilicate_glass

That was a very informative and interesting read Bojan

Especially when it got to

“Many current glass sex toys use high grade Borosilicate glass. The toys are generally hand blown, their beauty combined with the ease of cleaning and a long service life make them a popular material.”

Enlightening to say the least

[Shark Bait (Stu)]

The primary mirror in my SW 12" reflector is made of pyrex. It was not provided with cooling fans at manufacture as it is claimed that it will match ambient air temperatures fairly quickly. I have not tested this claim with any diagnostic equipment but I have not needed to add a fan at this stage.

Another BAS member has the 14" version of my scope and he has added three fans under his primary mirror as well as digital temp readouts.

I am sure that my mirror wasn't hand blown......

[andrew2008]

Don't have a fan on my 12" but have been looking at adding one lately. Would be interested to hear any other observations people have on the Pyrex mirrors apparently not needing a fan.

[brian nordstrom (As avatar)]

Remember in the old days when Mum started cooking pies , cakes , bread in Pyrex cooking dishes ? .
And not the cast iron stuff ? .
I do , showing my age here .
Anyway the same science applies here , its all about thermal expansion , eg. how much something expands and contracts as it heats and cools ( excited atoms in the material ) .
Pyrex's thermal expansion is about 1/2 that of plate glass so its " figure " holds true better when temperture's change , so the images we se are better ( until every thing reaches thermal equilibrium in your optric's train ) .
Thats why Mum likes cooking with Pyrex , the cakes , pies and breads fall out of the dishes easier because Pyrex does not expand and contract as much as plate glass , and heaps less than steel .
The cakes and stuff dont get squashed and broken getting them out of the dish . .
Thats the science .
Tastes good too . .
Brian.

[Shiraz (Ray)]

might also like to read this if you are concerned about glass types.
http://www.skyandtelescope.com/howto...tml?page=2&c=y

[Waxing_Gibbous (Peter)]

On my 12" dob to ambient ( 10-13C diff in temp):
No fan - Never (more than 45 mins)
Fan - 18-25 mins.

On my 8" Mak:
No Fan - Never
Fan - 20-25 Minutes.

If left outside the dob (open tube) will hit ambient w/o a fan in about an hour to an hour and a half. The Mak about 2 hours.

My experience only, YMMV, but for the extremely low current drain and limited noise, its hard to see the value in NOT having a fan.

[slowflow (Barry)]

both of those were worth a read with more answers than I had questions