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Mirror blank: How thin can you go?

Started by sopticals, 05/19/2010 02:04AM
Posted 05/19/2010 02:04AM Opening Post
[Hi I am planning on buying a 22" diameter by 3/4" thick floatglass mirror blank to make into a f5.75-f6 mirror for a budget Dob. Cost of glass to my door about US$250. This thickness ratio of 29.3:1 has been exceeded by at least one amature group in that a working Dob is in operation in the UK having a 30"X1" plate glass primary. I have heard that some of the "Very Large Telescopes" go to 40:1 and even 80:1. I saw somewhere that John Dobson figured a 24"X3/4" mirror and thats ratio 32:1. I am in New Zealand down under where thick glass is unobtainable. To import thicker or better blanks from overseas is beyond my present budget. For instance on one quote I got for supply of 20.25"X1.25" quartz was over US$2000. Looking forward to any and all input.B][/B]