Re: [ATM] A Null Test

["Donald Good" <donald.good@comcast.net>]

Richard;
So how does this compare to the Ross Null Test?  Advantages?  Disadvantages?
Is it more accurate?  Does it cover a wider range of conic constants?  f#s?
The example prescription given is for conic constant=-1.2 and f/2.5.  Do the
lens separations need to be adjusted for each change in cc and/or f#?  Since
this has more than 10 surfaces, those of us who use OSLO-LT will have
difficulty.
Thanks

-----Original Message-----
From: atm-bounces@atmlist.net [mailto:atm-bounces@atmlist.net] On Behalf Of
Richard F.L.R. Snashall
Sent: Saturday, September 02, 2006 10:36 PM
To: ATM List
Subject: [ATM] A Null Test

I thought I'd present some early findings...

...

The basic layout of the test is similar to a Ross Null Test in that the
light passes through the three lenses on both the forward and return
directions  (See Peter Ceravolo's article.).  For these setups, I selected a
500 mm diameter mirror with conic constants of -0.8 to -1.2.
This range of conics constants cover most of several designs:
Ritchey-Chretien (both Cassegrain and Gregorian), Classical Cassegrain, and
Newtonian.  The LPX309 planoconvex lens is nearest the source/knife with the
LPK065 planoconcave lens in the middle.  An example prescription
is:

Surf      Radius   Thickness    Glass    Diameter   Conic   Note

 OBJ     298.476     76.2331                    4       0   source
   1    Infinity        10.4      BK7          95       0   LPX309
   2     -155.62    29.31369                   95       0
   3    Infinity           3      BK7        94.2       0   LPK065
   4    311.2356    35.82609                 94.2       0
   5    Infinity        14.1      BK7       101.6       0   LPX303
   6     -131.75    2035.169                101.6       0
 STO    Infinity    12.49376                  500       0   stop at 
mirror edge
   8       -2500   -12.49376   MIRROR         500    -1.2   mirror
   9    Infinity   -2035.169                  500       0
  10     -131.75       -14.1      BK7    98.14704       0   LPX303
  11    Infinity   -35.82609             96.33898       0
  12    311.2356          -3      BK7    75.90638       0   LPK065
  13    Infinity   -29.31369             74.31415       0
  14     -155.62       -10.4      BK7    59.47545       0   LPX309
  15    Infinity    -76.2331             56.18785       0
 IMA     298.476                         4.009802       0   knife

...

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