I thought I would briefly share my experience of this glass v plate and pyrex.
i just completed a 13.25 inch f-5.6 mirror with the glass and I'm reasonably happy with the scopes performance.
However I ran into a number of interesting problems with the glass in terms of polishing and especially the figuring stage.
The glass was very difficult to get a really smooth polish and i went for softish pitch in the end and finished the figuring with a full tool used along with a 4 inch starlap type tool.
I ended up over correcting and coming back with accentuated pressure full tool on top.
Found this smoothed the surface but I struggled to get repeatable measurements when i rotated the mirror. Pyrex is far more predictable and overall was easier to use.
I did a 13 inch f-6 with pyrex for a friend first and it was a walk in the park when compared to the BVC.
It is soft and prone to sleeking. i never got rid of all the sleeking on the surface. I am however happy with the views and appear to have got close with the figure.
It polishes fast but is prone also to astigmatism if not careful. I had varations in the order of 15-20 % in terms of the caustic zone from centre to edge after intial figuring. I got this much closer with patience and care but I have never experienced anything like this variance with Pyrex or plate.
I would not use this glass again because of the figuring problems it took a long time to get a reasonable even figure. The more experienced amongst you may be able to tame it better but I know one very serious atmer who has done work including wright schmidt scopes who had the same problem.
One positive is the very quick cooldown when out in the field it does what itr says and is clearly at least as stable re temperature than pyrex.
One last thing the glass is slumped to form a shape and should never be ordered and then ground as it consists of 1/4 inch sheets baked together.
i just completed a 13.25 inch f-5.6 mirror with the glass and I'm reasonably happy with the scopes performance.
However I ran into a number of interesting problems with the glass in terms of polishing and especially the figuring stage.
The glass was very difficult to get a really smooth polish and i went for softish pitch in the end and finished the figuring with a full tool used along with a 4 inch starlap type tool.
I ended up over correcting and coming back with accentuated pressure full tool on top.
Found this smoothed the surface but I struggled to get repeatable measurements when i rotated the mirror. Pyrex is far more predictable and overall was easier to use.
I did a 13 inch f-6 with pyrex for a friend first and it was a walk in the park when compared to the BVC.
It is soft and prone to sleeking. i never got rid of all the sleeking on the surface. I am however happy with the views and appear to have got close with the figure.
It polishes fast but is prone also to astigmatism if not careful. I had varations in the order of 15-20 % in terms of the caustic zone from centre to edge after intial figuring. I got this much closer with patience and care but I have never experienced anything like this variance with Pyrex or plate.
I would not use this glass again because of the figuring problems it took a long time to get a reasonable even figure. The more experienced amongst you may be able to tame it better but I know one very serious atmer who has done work including wright schmidt scopes who had the same problem.
One positive is the very quick cooldown when out in the field it does what itr says and is clearly at least as stable re temperature than pyrex.
One last thing the glass is slumped to form a shape and should never be ordered and then ground as it consists of 1/4 inch sheets baked together.
