Stella Lyra vs Quattro?

[AbsolutelyN]

I've been looking at the recent addition of f/4 Newtonians from First Light Optics under the Stella Lyra brand and am curious as to how they compare the SkyWatcher Quattro scopes.  One thing in particular that stands out is the mirrors themselves .... they are BK7 whereas SkyWatcher use Pyrex. My very basic understanding is that BK7 has different thermal properties. In terms of using the scope for astrophotography is the difference negligible or is the mirror quality significantly different? Any thoughts much appreciated. 

Edited March 13, 2022 by AbsolutelyN

[Guest]

The Stellerlyra sold by FLO are made by GSO.  On this side of the pond they go by several different names.  The have a reputation of being good scopes for their price point.  I have a Orion Skyline which is identical to one model that FLO is selling and it is a solid performer.  Here is a link that will provide you some info on them.

 

https://telescopenights.com/celestron-vs-orion-vs-skywatcher/

[AstroMuni]

On 13/03/2022 at 17:37, AbsolutelyN said:

I've been looking at the recent addition of f/4 Newtonians from First Light Optics under the Stella Lyra brand and am curious as to how they compare the SkyWatcher Quattro scopes.  One thing in particular that stands out is the mirrors themselves .... they are BK7 whereas SkyWatcher use Pyrex. My very basic understanding is that BK7 has different thermal properties. In terms of using the scope for astrophotography is the difference negligible or is the mirror quality significantly different? Any thoughts much appreciated. 

Did you get any further with this? I am also interested in these and couldnt find much info.

[Craig a]

From what I understand is Pyrex has less chance or distorting with changes in temperature and is less dense than bk7 so bk7 holds heat for longer meaning a longer cool down when taken outside 

[tooth_dr]

My SW 250px was advertised as being made of Pyrex (I’m assuming the reason for the ‘x’ on the name). Other versions eg 250p don’t mention Pyrex, I wonder what they are made from?

[Louis D]

Since Pyrex changed from using borosilicate glass (looks colorless edge-on) to tempered soda lime glass (ordinary glass that looks green edge-on) with the 1998 divestiture of Corning's consumer division to World Kitchen LLC, I'm not sure it makes any difference.  Borosilicate glass is known for thermal shock stability, not necessarily gradual thermal stability.  Borosilicate glass's coefficient of thermal expansion is 6 times that of fused silica (quartz) glass, so it is more of a marketing ploy than anything else.  Besides, they can now use soda lime glass and call it Pyrex, so you don't really know what they're actually using.

By the way, if you are shopping for vintage Pyrex and want to make sure it is borosilicate glass, look for it to be colorless edge-on and for the brand to be PYREX all in upper case.  The newer soda lime glass versions are green edge-on and say pyrex all in lower case.

[Alan White]

From the web, Global Optics UK, they tell us this about BK7.

'BK7 is a glass with excellent optical quality. It is a hard material which is almost completely free of bubbles and other inclusions.
Borosilicate Crown Glass provides uniform transmission in the visible and a very high refractive index homogeneity.
Borosilicate Crown Glass – BK7 is typically used as a base material for precision optics, and for windows, lenses, and prisms.
It is also used as a substrate for mirror and filter coatings,  measurement and sensor-technology use.'

So in that case if the PYREX was Borosilicate Glass, I would deduce (rightly or wrongly) that BK7 is now much alike to the old PYREX and not the present pyrex which is soda lime glass.

 

[Craig a]

Don’t think it really matters about optical quality of glass for a mirror as the optical part is the shiny aluminium, what does matter for a mirror is it’s thermal quality and how smooth they grind the glass out for the Ali coating 

[Skyline]

On 13/03/2022 at 17:37, AbsolutelyN said:

I've been looking at the recent addition of f/4 Newtonians from First Light Optics under the Stella Lyra brand and am curious as to how they compare the SkyWatcher Quattro scopes.  One thing in particular that stands out is the mirrors themselves .... they are BK7 whereas SkyWatcher use Pyrex. My very basic understanding is that BK7 has different thermal properties. In terms of using the scope for astrophotography is the difference negligible or is the mirror quality significantly different? Any thoughts much appreciated. 

Skywatcher are using Borosilicate Glass in their Quattro 150P.

https://www.skywatcherusa.com/collections/telescopes/products/quattro-150p-imaging-newtonian-6

[Louis D]

Go out and do some ATM reading on mirrors, I just did myself.  Each glass type has its pros and cons.  I'm not sure there's a one best answer to which glass type is best for commercial grade mirrors.  For high end mirrors, fused silica (quartz) is probably the way to go.

Edited October 18, 2022 by Louis D

[newbie alert]

When I was thinking about a fast newt such as the quattro, the Lacerta model had a different glass, blackened edges but in a search the thin metal tube was a concern... Spec wise the TS model looked the best spec wise but that may have been the carbon fibre model and off the top of my head had fuzed silica

Edited October 18, 2022 by newbie alert
Added info