RE: [ATM] ATM Edmund secondary mirrors - worth it?

["Jerry" <wa4guu@verizon.net>]

	Both Edmund Scientific and Protostar state surface P-V at 633nm on
their websites.

	Nothing I am saying or have said should be taken as a negative
comment about Protostar. I haven't dealt with them and have no knowledge
good or bad about their products.

	I did go to their website and look at the diagonals and would say
they seem to state their quality specs fairly clearly. Actually I would say
very clearly except for one thing. As I read it they aren't guaranteeing but
there is "high confidence" that the diagonal you receive is at least as good
as the statistical average of a batch minus two standard deviations. It
looks like typical is about 1/14 wave in a batch and minimum accuracy about
1/11 wave and that variable from batch to batch. The 1.8" being out of stock
I guesstimated the typical and minimum from adjacent sizes. I didn't find
firm assurance that the diagonal one would receive would not be worse than
the two standard deviations subtracted from the average. I don't see a
return policy. Maybe I missed it. 

	It is to be expected that to reliably provide at least a certain
quality P-V surface some will be better than that.

	Now I am not blowing Edmund's horn here but they state clearly the
quality of their diagonals. They aren't saying there is some statistical
probability that you will receive a 1/8 wave or some other 1/x wave. They
just say that you will get no worse than 1/x P-V. Is it possible that their
typical might be a bit better also?

	My comment on the certification could have been taken wrong.
Certification may be more useful regarding instruments of a more critical
nature than an amateur flex mirror telescope.



Jerry
	


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