Quote:
Originally Posted by DavidU
These days I have seen some very nice mass produced mirrors from Skywatcher,GSO and Orion. I think the Chinese have perfected machine figuring to some degree. The beauty of this is it makes it an affordable hobby to get into.]
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Casual tests don't portray some of the fundamentals behind the typically 2X cost difference between the mass produced imports and custom made mirror, ( which are not just cheaper because of cheap labour and machine production . To achieve a fine optical surface that will last , you need to start with a low expansion substrate that is fine annealed .This slow cooling ( annealing ) is what costs money because it takes energy and it takes weeks.
As an optics professional that has tested a lot of this glass with a polarising light box , I see that these high expansion substrates used in the mass production scopes are all coarse ( fast ) annealed which is where a large part of the cost saving comes in. Without a stress free piece there is no long term guarantee about the stability of shape of the glass. Glass with internal stress also behaves unpredictably under different cooling gradients that are seasonal.
As a craftsmen though I can't work on a piece of glass with unknown longer term mechanical stability.
Mark