[ATM] Enhanced coatings

[Mike Lockwood <melockwo@uiuc.edu>]

Hi,

Mitchell R wrote:
> Indeed. I think that's one reason why enhanced coatings aren't recommended
> much. Unless doing astrophotography or something where the gain is more
> measurable. 

It starts to make sense when you have THREE reflective surfaces in a 
telescope, such as a Coude or Naysmith Cassegrain.

0.89^3 = 70.5% reflectivity
0.96^3 = 88.5% reflectivity

88.5/70.5 = 1.25 times more light, so 25% improvement.

The enhanced coatings on my 12.5" Cass optics are from L&L.  I have 
good, high-contrast views.  They are holding up nicely, but the scope 
is stored indoors.

The poor reputation of enhanced coatings seems to me to be undeserved. 
  Adding a layer of tantalum pentoxide shouldn't cause the problems 
that people report, should it?

	Mike Lockwood




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