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Re: [ATM] Quartz blanks

Earlier I posted a price for some 20 inch Fused Quartz blanks that I have available. I forgot to mention that this is very competative with the lowest price I could find from someone that had an honest-to-goodness storefront. 
   
  You can OCCASIONALLY see Fused Quartz optical pieces on eBay for a LOT LESS but rarely at this size and always with a disclaimer that the seller doesn't have the facilities to guarantee what he is selling and you have to take the chance on what you are getting...
   
  More importantly,
   
  I think Mike was wanting Quartz to eliminate a focus shift problem in an assembled instrument under actual operating conditions. I do not think that a Quartz blank alone will give him that. True, the quartz is going to be ultra stable (and a joy to work) but it's miniscule focal length change will be dwarfed by the CTE of the telescope/instrument that he puts it in. Wouldn't be fair to think you are home-free by spending $5K for glass if you are going to use aluminum truss tubes to hold the magnifying secondary out front.
   
  Once you commit to Quartz for the optics, you also have to commit to zero-expansion or compensating materials for the rest of the instrument or you've wasting your investment. While shopping for Quartz, it would be prudent to also shop for INVAR etc.
   
  Even so, I'm still entertaining offers for my glass.
   
  Ken Hunter
   
   

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