From: "CSC" 
To: "Atm" 
Reply-To: "CSC" 


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Blank8 inches is a good planetary size if the atmosphere is steady.  f/4 is
somewhat troublesome as is the 1/4 wave rating.  Planetary viewing is the
most exacting of the optical system, and the large obstruction of an f/4,
probably 30% of the diameter is a bit too big. It causes the same loss of
contrast as 1/4 wave error even with a perfect mirror.  Now add the
reported 1/4 wave and it will not likely deliver planetary quality images.
Being a newbie, the collimation requirements for f/4 are stringent, and
without lots of viewing experience, you may rarely collimate it well enough
to get the best images.  In all it would not make a good planetary scope.

I am constantly amazed by the detail available in long- focus newtonian
scopes, f/8 and up.  I have a 4.25 f/11 edmund scope that is refigured to
1/10 wave.  the images are fantastic (tho dim).

You'd better try f/6 or slower, and a 6"or 8" f/6-10 will be the
most usable scope.  The short focus scopes are of no interest to me,
generally, too fussy and not planetary quality.

Colin
  -----Original Message-----
  From: owner-atm{at}shore.net [mailto:owner-atm{at}shore.net]On Behalf Of none
  Sent: Wednesday, August 06, 2003 2:11 AM
  To: ATM
  Subject: ATM 8in Mirror Specs


  Hello, all: Just curious what some of you think of the specs for this
mirror are what would be called "acceptable."  Being somewhat a
newbie, I'm assuming from what I've read that this would be a better mirror
for planetary use.  Thanks for your time and for contributing to The List. 
John

  8"Mirror

  f=750

  power=6

  surface accuracy=1/4 lambda

  Full Coating: al+sio

  scratch-dig=60/40

  chamfer 1x45'

  clear aperture 8inches = 203mm


  focal length 29.39inches = 750mm


  focal ratio f/4


  mirror thickness 0.75inches = 19mm


  thickness/diameter ratio 1:10.5



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8 inches is a good planetary size =
if the=20
atmosphere is steady.  f/4 is somewhat troublesome as is the 1/4 = wave=20
rating.  Planetary viewing is the most exacting of the optical =
system, and=20
the large obstruction of an f/4, probably 30% of the diameter is a bit = too big.=20
It causes the same loss of contrast as 1/4 wave error even with a = perfect=20
mirror.  Now add the reported 1/4 wave and it will not likely = deliver=20
planetary quality images.
Being a newbie, the collimation =
requirements=20
for f/4 are stringent, and without lots of viewing experience, you may = rarely=20
collimate it well enough to get the best images.  In all it would
= not make=20
a good planetary scope.
 
I am constantly amazed by the =
detail=20
available in long- focus newtonian scopes, f/8 and up.  I have a =
4.25 f/11=20
edmund scope that is refigured to 1/10 wave.  the images are =
fantastic (tho=20
dim).
 
You'd better try f/6 or slower, =
and a 6"or=20
8" f/6-10 will be the most usable scope.  The short focus
scopes = are of no=20
interest to me, generally, too fussy and not planetary =
quality.
 
Colin

  -----Original Message-----From: =
owner-atm{at}shore.net=20
  [mailto:owner-atm{at}shore.net]On Behalf Of
noneSent:=20
  Wednesday, August 06, 2003 2:11 AMTo: =
ATMSubject: ATM=20
  8in Mirror Specs
  Hello, all: Just curious what some of you think of the specs for =
this=20
  mirror are what would be called "acceptable."  Being
somewhat a =
newbie,=20
  I'm assuming from what I've read that this would be a better mirror =
for=20
  planetary use.  Thanks for your time and for contributing to The=20
  List.  John
   
  8"Mirror
   
  f=3D750
   
  power=3D6
   
  surface accuracy=3D1/4 lambda
   
  Full Coating: al+sio
   
  scratch-dig=3D60/40 
   
  chamfer 1x45'
   
  clear aperture 8inches =3D 203mm
   
  focal length 29.39inches =3D 750mm
   
  focal ratio f/4
   
  mirror thickness 0.75inches =3D 19mm
   
  thickness/diameter ratio 1:10.5
   

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