The guide fiber assembly consists of 42 1/16'' ferrules. Two sets of 6 ferrules are mounted in an array and viewed by a camera. Each of these sets surrounds a single science fiber in the telescope's focal plane. When a target star is slightly misaligned with the desired science fiber, some of the stellar light will be seen in one or more guide fibers, and therefore tell the observer in which direction the telescope needs to be moved to center the target star. Because a relatively large area must be imaged onto the guide system camera (SBIG STV), an optical system was desined to provide approximately ~3.3X demagnification of the guide fiber ferrules. The remaining 30 guide fibers are mounted out of the way. Their corresponding science fibers are used to collect sky background.

To minimize expense, 2 off-the-shelf Edmund Industrial Optics achromatic doublets were used for this design. The layout can be viewed here.

A spot diagram is available here.

A ZEMAX file is also available.

System/Prescription Data

Title: Guide Fiber Monitoring System (2 achromats)
Date : WED AUG 27 2003

LENS NOTES:

       This design uses Edmund Industrial Optics lenses and provides ~3.3X
       demagnification from the guide fiber mount plane to the STV CCD.

GENERAL LENS DATA:

Surfaces                :                8
Stop                    :                4
System Aperture         : Float By Stop Size = 11
Glass Catalogs          : SCHOTT HOYA
Ray Aiming              : Off
Apodization             : Uniform, factor =   0.00000E+000
Effective Focal Length  :         7184.62 (in air at system temperature and pressure)
Effective Focal Length  :         7184.62 (in image space)
Back Focal Length       :       -2133.203
Total Track             :        180.9378
Image Space F/#         :        77.58252
Paraxial Working F/#    :        1.362138
Working F/#             :        1.320633
Image Space NA          :       0.3445884
Object Space NA         :       0.1094593
Stop Radius             :             -11
Paraxial Image Height   :               3
Paraxial Magnification  :            -0.3
Entrance Pupil Diameter :        92.60617
Entrance Pupil Position :       -510.8895
Exit Pupil Diameter     :        27.30249
Exit Pupil Position     :       -35.93992
Field Type              : Object height in Millimeters
Maximum Field           :              10
Primary Wave            :       0.5875618
Lens Units              :   Millimeters
Angular Magnification   :       -3.391858

Fields          : 3
Field Type: Object height in Millimeters
#        X-Value        Y-Value         Weight
 1       0.000000       0.000000       1.000000
 2       0.000000       5.000000       1.000000
 3       0.000000      10.000000       1.000000

Wavelengths     : 3
Units: Microns
#          Value         Weight
 1       0.486133       1.000000
 2       0.587562       1.000000
 3       0.656273       1.000000

SURFACE DATA SUMMARY:

Surf     Type         Comment    Radius  Thickness    Glass  Diameter  Conic
 OBJ STANDARD                  Infinity   90.41489                 20      0
   1 STANDARD  (-)EDSCI 45353    446.01          4     SF10        50      0
   2 STANDARD                     46.95      13.92   BAFN10        50      0
   3 STANDARD                    -69.28   123.0444                 50      0
 STO STANDARD                  Infinity          5                 22      0
   5 STANDARD     EDSCI 45211     21.17      11.04   BAFN10        25      0
   6 STANDARD                    -16.08          3     SF10        25      0
   7 STANDARD                   -118.66   20.93339                 25      0
 IMA STANDARD                  Infinity                      6.414694      0