ATM buying the secondary

["Nik Cain" <N.J.Cain@sheffield.ac.uk>]

Hi, I've been looking through the archives and saw that buying rather 
than making the secondary was an easier option. I've got the 
catalogues for Ealing and for Newport, and it looks like Ealing is 
the cheaper company. Ealing claims lambda/8 for their mirrors, while 
Newport has lambda/10. I wasn't quite sure how to take these numbers 
really - are they more than suitable, is it unimportant as long as 
the variation is less than the variation in the primary? They also 
quoted a surface quality in terms of scratch-dig, the ealing being 
60-40 and the newport being 15-5. I figured from the blurb that lower 
the numbers the better, but other than that it was pretty vague. 
Anybody want to explain these numbers?

Nik 


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Dr Nik Cain             Tel: +44 (0)114 2223599
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