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

[Ken Lowther <hermit@outofoptions.org>]

I remember talking to Bryan when he started Protostar.  He searched to 
make sure that he could offer a quality product.  He even paid to get 
some scratch/dig figures.  It wasn't cheap.

Bottom line is, if you can't test your own, then you really don't know 
what  you get.  Seems as though some vendors can inflate numbers 
because they know you will not have something independently tested and 
most folks won't know if something is not up to spec.

Ken

Quoting 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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