Keck Observatory Technical Note 163

Optical Parameters of the Keck Telescope

Jerry Nelson

7 January 1986

Revision 1 19 May 1988

Revision 2 18 July 1989

Revision 3 24 June 1991

File: Optical Parameters R3

Introduction

����������� The completion of a set of 6 segments at Itek has occasioned a slight change in the radius of curvature of the primary mirror which is included here. We do no not expect that the primary mirror parameters will change any further. These values and those given for each of the segments are the same as those given in a previously distributed note dated 17 April 1989. Included in this note are segment descriptions for both the final segment with a = 0.9m and for the uncut mirrors with a = 0.95m.

����������� The f/15 secondary is in the process of fabrication. To minimize the material removal during aspherizing of the secondary, the radius of the curvature of the f/15 secondary has been changed slightly. This is included below. The indicated values are similar to those given by Epps in a 14 March 1989 letter, and extremely close to those given to me by Epps in a 13 July 1989 telephone conversation. The radius of curvature of the secondary may still change somewhat during the fabrication process (up to 70mm, probably substantially less) so these parameters are not final.

����������� In this third revision, I have added the radius of curvature of the focal surfaces. This was inadvertently left out in the last version. For f/15 and for f/25 the focal surface is concave as seen from the secondary. I have also made a few minor format clarifications that were inadvertently omitted in the version sent to you a week ago.

Calculate parameters defining telescope optical surfaces (created 30jan89, last mod 24jun91) not quite a Rithey-Chretien system at f/15. (independently defined primary)

Primary Parameters

Radius of Curvature k(m)� 34.9740
Primary mirror dia. DP(m) 10.949
Primary conic const CC -1.003683

f/15 Secondary Parameters

Back focal distance e(m) 2.5000 del 0.14296334 2e/k
Final focal length f(m) 149.583 m 8.55394865 2f/k
Primary-sec. Dist d(m) 15.394985      
Sec. Rad. Of Curvature k2(m) -4.737916      
Sec. Conic const. SCC -1.644326      
Focal radius of curv. 1/km (m) 2.123573      
f/15 FOV radius FV1 (�) 10.00      
Secondary dia 0� FOV DS0 (m) 1.309857      
Secondary dia inc FOV (m) 1.399421      
Coma at 10� radius ATC (�) -0.005      
Astigmation at 10� radius AAST (�) 0.506      
Field size for 20� FOV (m) 0.870      

f/25 Secondary Parameters

Back focal distance e(m) -4.538 delp -0.2595071 2e/k
Final focal length f(m) 250.000 mp 14.2963344� 2f/k
Primary-sec. Distance d(m) 16.640457      
Sec. Rad. Of curvature� k2(m) -1.820420      
Sec. conic const. SCC -1.418029      
Focal radius of curv. 1/km (m) 0.808794      
f/25 FOV radius FV1 (�) 5.00      
Secondary dia 0� FOV DS0 (m) 0.530039      
Coma at 5� radius ATC (�) 0.690      
Astigmatism at 5� radius AAST (�) 0.233      
Field size for 10� FOV (m) 0.727    

Primary Segments

a(m) 0.9        
Segment Type Type 1 Type 2 Type 3� Type 4,5 Type 6
R(m)(oad)� 1.55885� 2.70000 3.11769 4.12432 4.67654
R/k (ep) 0.04457156� 0.07720021 0.08914312 0.11792526 0.13371468
cc*ep^2 -0.0019939 -0.0059818 -0.0079758 -0.0139576 -0.0179455
1-cc*ep^2 1.001994 1.005982 1.007976 1.013958 1.017945

Zernike Coefficients of Segments (microns)

C20 5778.499 5755.625 5744.265� 5710.485 5688.212
C22� -11.505 -34.310 -45.611 -79.114 -101.122
C31 -4.419 -7.572 -8.695 -11.318 -12.695
C33 0.007 0.034 0.052 0.118 0.170
C40 0.001 0.004 0.006 0.012 0.015
C42 0.002�� 0.006 0.007 0.013 0.016
C44 0.000 0.000 0.000 0.000 0.000

Primary Segments

a(m) 0.95        
Segment Type� Type 1� Type 2 Type 3� Types 4,5 Type 6
r(m) (oad) 1.55885� 2.70000 3.11769� 4.12432 4.67654
r/k (ep) 0.04457156 0.07720021 0.08914312 0.11792526 0.13371468
cc*ep^2 -0.0019939 -0.0059818 -0.0079758 -0.0139576 -0.0179455
1-cc*ep^2 1.001994 1.005982 1.007976 1.013958 1.017945

Zernike Coefficients of Segments (microns)

C20 6438.389 6412.905 6400.248 6362.613 6337.798
C22 -12.818 -38.226 -50.816 -88.144 -112.663
C31 -5.198 -8.905 -10.227 -13.311 -14.931
C33 0.008� 0.040 0.061 0.139 0.200
C40 0.001 0.006 0.008 0.014� 0.019
C42 0.002 0.007 0.009 0.016 0.020
C44 0.000� 0.000� 0.000 0.000 0.000

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