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Re: [ATM] A Null Test
Hi Richard,
Sunday, September 3, 2006, 1:50:24 PM, you wrote:
RS> I thought I'd present some early findings...
RS> ...
RS> The basic layout of the test is similar to a Ross Null Test in that the
RS> light passes through the three lenses on both the forward and return
RS> directions (See Peter Ceravolo's article.). For these setups, I selected a
RS> 500 mm diameter mirror with conic constants of -0.8 to -1.2.
RS> This range of conics constants cover most of several designs:
RS> Ritchey-Chretien (both Cassegrain and Gregorian), Classical Cassegrain, and
RS> Newtonian. The LPX309 planoconvex lens is nearest the source/knife with the
RS> LPK065 planoconcave lens in the middle. An example prescription
RS> is:
RS> Surf Radius Thickness Glass Diameter Conic Note
RS> OBJ 298.476 76.2331 4 0 source
RS> 1 Infinity 10.4 BK7 95 0 LPX309
RS> 2 -155.62 29.31369 95 0
RS> 3 Infinity 3 BK7 94.2 0 LPK065
RS> 4 311.2356 35.82609 94.2 0
RS> 5 Infinity 14.1 BK7 101.6 0 LPX303
RS> 6 -131.75 2035.169 101.6 0
RS> STO Infinity 12.49376 500 0 stop at
RS> mirror edge
RS> 8 -2500 -12.49376 MIRROR 500 -1.2 mirror
RS> 9 Infinity -2035.169 500 0
RS> 10 -131.75 -14.1 BK7 98.14704 0 LPX303
RS> 11 Infinity -35.82609 96.33898 0
RS> 12 311.2356 -3 BK7 75.90638 0 LPK065
RS> 13 Infinity -29.31369 74.31415 0
RS> 14 -155.62 -10.4 BK7 59.47545 0 LPX309
RS> 15 Infinity -76.2331 56.18785 0
RS> IMA 298.476 4.009802 0 knife
I'm commenting in the dark a little, Richard, as I didn't see
your original post, only Donalds follow up. This looks like an
OIffner Null test, but with three lenses rather than two. What
does the extra lens do?
Here's the Offner setup I traced for a 16" RC primary :
Surf Radius Thickness Glass Diameter Conic
OBJ Infinity 518.5576 0 0
1 Infinity 10 BK7 50 0
2 -77.52 185.6841 50 0
3 417.54 5 BK7 24 0
4 -417.54 20.66401 24 0
5 Infinity 2400 1.669547 0
STO -2400 -2400 MIRROR 400 -1.144162
7 Infinity -20.66401 1.669708 0
8 -417.54 -5 BK7 24 0
9 417.54 -185.6841 24 0
10 -77.52 -10 BK7 50 0
11 Infinity -518.5534 50 0
IMA Infinity 0.000714256 0
A good merit function operand to use is RAID on the mirror, and
TRAX, after using PMAG to ensure unity magnification.
--
Best regards,
Richard in the UK
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