FOBOS Guide System
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Description: The FOBOS guide system is housed in the focal plane
module. Its purpose is to allow fine adjustment of target star alignment on
the science fiber, and to monitor guiding during exposures. The system path
within the focal plane module is highlighted in pink in the figure below.
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.
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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
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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.
