Re: [ATM] The standard aluminium coating: How much scatter?

[Anthony Stillman <atmer@flash.net>]

Guntram,

I plowed through all the relevant books and papers I
have at home and found almost nothing about surface
scatter.  As you mentioned at the beginning of the
thread Texereau has a few qualitative paragraphs here
and there on this subject.  I do remember a paper from
some years ago in ?Optical Engineering? specifically
about scatter and coatings.  And I haven?t found it. 
In a discussion of a multi-mirror system (a
sheepsprinkler) Kevin Medlock pointing out this
inherent fault in mirrored systems and told me an
overcoat of magnesium fluoride will suppress the
problem as much as it can be.

Two books which did contain enough information to form
an approximate value for the scatter from an over
coated aluminized surface are the ?Handbook of Optics?
and the ?Handbook of Military Infrared Technology? 
Both books are known for their numerous errors.  From
the information contained there in I divined that
scatter represents between -3% and 10% of the lost
light.

I also did a web search and came across this site:

<http://www.ctio.noao.edu/telescopes/opteng/reflec4m.html>

Here actual experimental values have been collected
for the 4m Victor Blanco telescope.  This data places
the scattered loss between 0.5% and 10% dependent upon
the age and cleanliness of the coating.  

Anthony


tempus erit, quo vos speculum vidisse pigebit
                       -Ovid  43 BC ? AD 17
The time will come when you will be sorry to have
looked into your mirror.

(Pretty much every time I put it on the test stand.)

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