I am in the final stretch to obtain all the components for my Lightholder 10" f6 primaried Dobson. But this last item has really kind of given me mixed decision. I have read as much as I could about both, but I would really appreciate some experianced advice on this. I purchased what I believe is a top primary so it only goes to think which diagonal is best suited to compliment the primary.Thank you all for any advice you may send my way. Allen
Pyrex vs Quartz diagonal
Started by elfy46, 12/19/2007 07:05PM
Posted 12/19/2007 07:05PM
Opening Post
Posted 12/19/2007 07:50PM
#1
Hi Al,
I have had both types of secondary mirrors. They are both quite good. Quartz is fused silica and can be polished with a greater precision, so the surface can be very smooth. Pyrex is almost as good in this regard, but because it is a softer material, it does not polish quite as smoothly.
Quartz is also better about thermal stability, so it has an edge on that over Pyrex.
I have had 1/30 wave secondary mirrors of both materials and it was difficult to see a real difference between them. I was very pleased both mirrors. The Quartz mirror made a huge difference in the scope performance, but that was due to the poor secondary it replaced more than the Quartz.
I would say, buy a better rated (Wave Front P/V) Pyrex mirror for the same amount of money that you would have spent on the Quartz mirror. A better wave front is probably worth more than the difference in materials. So if you can get a 1/30 wave Pyrex for the cost of a 1/15 wave Quartz, go with the Pyrex.
My $.02. 8)
I have had both types of secondary mirrors. They are both quite good. Quartz is fused silica and can be polished with a greater precision, so the surface can be very smooth. Pyrex is almost as good in this regard, but because it is a softer material, it does not polish quite as smoothly.
Quartz is also better about thermal stability, so it has an edge on that over Pyrex.
I have had 1/30 wave secondary mirrors of both materials and it was difficult to see a real difference between them. I was very pleased both mirrors. The Quartz mirror made a huge difference in the scope performance, but that was due to the poor secondary it replaced more than the Quartz.
I would say, buy a better rated (Wave Front P/V) Pyrex mirror for the same amount of money that you would have spent on the Quartz mirror. A better wave front is probably worth more than the difference in materials. So if you can get a 1/30 wave Pyrex for the cost of a 1/15 wave Quartz, go with the Pyrex.
My $.02. 8)
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