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Originally Posted by Satchmo
Hi Rolf- I guess the desihn varies according top the size - I made a 14.5" conical with blank from same source as Royce and was surprised to find it similar in weight to the 14 " X 1.6" I had on hand . I will check your calcs tomorrow- that would be good news if you are right .
The 16" Is a beast with the central flat nearly 8" dioameter and 60mm thick and the edge about 20mm ..it was pretty heavy .
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Hi Mark,
I have put it all in a spreadsheet and also calculated for your 16" conical. Based on the dimensions you gave it would have a volume of 243 cubic inches. A 16" flat at 1.6" thick (can at 16" be that thin?) would have a volume of 340 cubic inches, so is still much heavier.
The philosophy of conical mirrors is that most of the glass towards the edge serves no purpose for support and hence it is removed. A conical is typically only a little thicker in the centre than a corresponding flat, but all the shaved off glass more than makes up for this so conicals are much lighter.
Further to this, because the conical has only a relatively small flat back in the middle (where it is comparatively thick) it can be mounted flat against a plate with a bolt. This saves further weight and complexity for mounting hardware and also makes collimation extremely stable.
In addition, the air is free to move around the conical mirror because it's not mounted in a cell. So it reaches thermal equillibrium faster and also keeps it very vell.
I think the above is what exactly makes a "good product".
IMHO it's the perfect mirror design and I really don't understand why there are not more conical mirror makers out there.
While I'm no expert it did sound like you had handled a fair number of conicals in order to come to this conclusion:
Quote:
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Originally Posted by Satchmo;
Ive never seen one any lighter than a standard 1.6 inch plano blank in the same size
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Is that based on empirical testing or is it gut feel? I'm asking because I just can't get the math to stack up in favour of flat mirrors at all.