I was thinking of an upgrade with a quality quartz secondary,mainly because of the excellent surface polish they have. Has anyone had good results with this type of upgrade?
ULS quartz secondary upgrade
Started by DavidU, 05/11/2003 12:18AM
Posted 05/11/2003 12:18AM
Opening Post
Posted 05/11/2003 02:31PM
#3
I installed one of these and it was definitly
a "downgrade." The mirror had a small
un-aluminimzed region at the edge (most of them
do). At first I didn't think it would matter,
but it makes a huge diffration spike across the
field on anything bright. Very expensive mistake.
a "downgrade." The mirror had a small
un-aluminimzed region at the edge (most of them
do). At first I didn't think it would matter,
but it makes a huge diffration spike across the
field on anything bright. Very expensive mistake.
Posted 05/12/2003 12:40AM
#4
David,
You don't say how good the surface accuracy of your current mirror is-- going from a run of the mill 1/10 wave secondary-- possibly with a turned down edge-- to the typical "quartz quality" uniformity of flatness will make a huge difference. IMO this is probably even more significant than the backscatter reduction from the smoother polish. I recently upgraded an indifferent quality (and poorly mounted) Meade 4" secondary to a high quality (1/15th wave, 1/100 RMS, Zygo certified) Pyrex 3.1" one, and the difference was like night and day! Together with a 0.25" masking of my primary to cover the mirror clips and a TDE, I was able to *double* my useful magnification ceiling from 360X to 700X on a 16" scope. I'm beeh toying around with the idea of having a custom-made 1/20 wave 3.1" quartz diagonal made to see if it yields any further performance increase over the Pyrex one. I probably wouldn't see the difference in performance more than a couple of times per year, at best.
Jim
You don't say how good the surface accuracy of your current mirror is-- going from a run of the mill 1/10 wave secondary-- possibly with a turned down edge-- to the typical "quartz quality" uniformity of flatness will make a huge difference. IMO this is probably even more significant than the backscatter reduction from the smoother polish. I recently upgraded an indifferent quality (and poorly mounted) Meade 4" secondary to a high quality (1/15th wave, 1/100 RMS, Zygo certified) Pyrex 3.1" one, and the difference was like night and day! Together with a 0.25" masking of my primary to cover the mirror clips and a TDE, I was able to *double* my useful magnification ceiling from 360X to 700X on a 16" scope. I'm beeh toying around with the idea of having a custom-made 1/20 wave 3.1" quartz diagonal made to see if it yields any further performance increase over the Pyrex one. I probably wouldn't see the difference in performance more than a couple of times per year, at best.
Jim
Funding Member
