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Some General Considerations on Wide Field Telescopes Dirk Soltau Kiepenheuer-Institut für Sonnenphysik Synoptic Network Workshop, Boulder 22.-24.4.2013 1
Synoptic Network Workshop, Boulder 22.-24.4.2013
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Some General Considerations on Wide Field Telescopes
Dirk SoltauKiepenheuer-Institut für
Sonnenphysik
Synoptic Network Workshop, Boulder 22.-24.4.2013
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Basic assumptions and immediate conclusions
• Detector size: 4k x 4 k pixels, 5 µm pixel size• Field of view: 0.7° 2500 arcsec
• pixelscale = 0.6 arcsec• image scale = 120 arcsec/mm• focal length = 1720 mm
Synoptic Network Workshop, Boulder 22.-24.4.2013
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Diameter
• resolution according to sampling theorem: 1.2 arcsec = 5.8 µrad– D = 1.22 λ / 5.8E-6– minimum Diameter w.r.t resolution = 0.1 m
Synoptic Network Workshop, Boulder 22.-24.4.2013
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Bandwidth, SNR• Assumed bandwidth: 5 pm ( 50 mÅ, R = 100000 @ 500 nm)• Assumed Exposure time: 0.005 s
Telescope
PBS Cam1
Cam2
F Ret
Sun
Synoptic Network Workshop, Boulder 22.-24.4.2013
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Counts and SNR for 5 ms exp. time
Aperture wavelengthλ = 5 pm
Heat load Photoelectrons SNR
0.1 m 400 nm 10 W 4500 70
0.5 m 400 nm 200 W 110000 350
1.0 m 400 nm 1000 W 450000 670
0.1 m 630 nm 10 W 9000 100
0.5 m 630 nm 200 W 230000 480
1.0 m 630 nm 1000 W 900000 950
Diameter should exceed 0,5 m f/# < f/3.5
Synoptic Network Workshop, Boulder 22.-24.4.2013
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Mounting (common instrument platform)
• May be we need different instruments for different SNR requirements (Polarimetry vs. imaging)
• Several instruments on one platform may be a solution
SOLIS
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Image Motion and Noise
0.1 m
0.1 m
1 m
1 m
Sun = 104 isoplanatic patches Average seeing induced image motion of the whole disk will be around 0.01 pixel
2 pixel
1 pixel
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Time constant
0.1 m
1 m
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Image motion: Effect on image subtraction
=-
Image stabilization needed, dual beam polarimetry desirable
Example: shift by 0.1 pixel 10-2 noise
Synoptic Network Workshop, Boulder 22.-24.4.2013
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Image stabilization?
• Main cause probably instrumental:– spatial dimensions: 1m 1 arcsec = 5 µm at the mirror
edge• Limb sensor vs. Correlation tracker• Tiptilt mirror
– relay optics?– Solar Orbiter (PHI) concept?
Synoptic Network Workshop, Boulder 22.-24.4.2013
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Optical Design Options
• Design driving parameters:– Detector– SNR @ typical exposure time
Synoptic Network Workshop, Boulder 22.-24.4.2013
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Refractor
• Good performance, limited diameter
Example: Chrotel (KIS)
Synoptic Network Workshop, Boulder 22.-24.4.2013
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Example: Maksutov
D . S o l t a uK I S
M a k s u t o v . Z M XC o n f i g u r a t i o n 1 o f 1
3 D L a y o u tM A K S U T O V , D = 2 0 0 m m , f / 1 02 1 . 0 4 . 2 0 1 3
X
Y
Z
0 2 4 6 8 1 0 1 2 1 4 1 6 1 8 2 00 . 0
0 . 1
0 . 2
0 . 3
0 . 4
0 . 5
0 . 6
0 . 7
0 . 8
0 . 9
1 . 0
R a d i u s F r o m C e n t r o i d i n µ m
0 . 0 0 0 0 ( d e g )0 . 2 5 0 0 ( d e g )
D . S o l t a uK I S
M a k s u t o v . Z M XC o n f i g u r a t i o n 1 o f 1
Fraction of Enclosed Energy
G e o m e t r i c E n c i r c l e d E n e r g yM A K S U T O V , D = 2 0 0 m m , f / 1 02 1 . 0 4 . 2 0 1 3W a v e l e n g t h : P o l y c h r o m a t i cD a t a h a s b e e n s c a l e d b y d i f f r a c t i o n l i m i t .S u r f a c e : I m a g e
+ Potential for evacuation-
D = 200 mm, FOV = 0.5 deg
10 µm
Synoptic Network Workshop, Boulder 22.-24.4.2013
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Example: Ritchey-Chretien Cassegrain
D . S o l t a uK I S
D i r k s R C _ 0 3 . Z M XC o n f i g u r a t i o n 1 o f 1
3 D L a y o u t R i t c h e y - C h r e t i e n w i t h f = 1 9 0 0 m m , D = 6 0 0 m m2 1 . 0 4 . 2 0 1 3
X
Y
Z
0 2 4 6 8 1 0 1 2 1 4 1 6 1 8 2 00 . 0
0 . 1
0 . 2
0 . 3
0 . 4
0 . 5
0 . 6
0 . 7
0 . 8
0 . 9
1 . 0
R a d i u s F r o m C e n t r o i d i n µ m
- 0 . 2 0 0 0 , 0 . 2 0 0 0 ( d e g )0 . 0 0 0 0 , 0 . 2 8 0 0 ( d e g )
0 . 2 0 0 0 , 0 . 2 0 0 0 ( d e g )- 0 . 2 8 0 0 , 0 . 0 0 0 0 ( d e g )
0 . 0 0 0 0 , 0 . 0 0 0 0 ( d e g )
0 . 2 8 0 0 , 0 . 0 0 0 0 ( d e g )- 0 . 2 0 0 0 , - 0 . 2 0 0 0 ( d e g )
0 . 0 0 0 0 , - 0 . 2 8 0 0 ( d e g )
0 . 2 0 0 0 , - 0 . 2 0 0 0 ( d e g )
D . S o l t a uK I S
D i r k s R C _ 0 3 . Z M XC o n f i g u r a t i o n 1 o f 1
Fra
cti
on of Enclose
d Energy
G e o m e t r i c E n c i r c l e d E n e r g y R i t c h e y - C h r e t i e n w i t h f = 1 9 0 0 m m , D = 6 0 0 m m2 1 . 0 4 . 2 0 1 3W a v e l e n g t h : P o l y c h r o m a t i cD a t a h a s b e e n s c a l e d b y d i f f r a c t i o n l i m i t .S u r f a c e : I m a g e
D = 600 mm, FOV = 0.5 deg
-Might need a field corrector if larger-needs baffling (daylight blindness)
Titisee 15
Consider different designs for different purposes
Several telescopes on a common structure
SOLIS concept
Synoptic Network Workshop, Boulder 22.-24.4.2013
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Summary
• Basic requirement: SNR• Image stabilization – if necessary – has large impact on
the design• Diameter not determined by resolution arguments
telescope doesn‘t need to be diffraction limited• Evacuation should be considered (catadioptric system?)• Multiple telescope platform might be useful• Ritchey-Chretien promising. But false light counter
measures necessary
Synoptic Network Workshop, Boulder 22.-24.4.2013
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Photon electronsSolar Spectral Irradiance from ASTM data in W/^m^2/nm 1,700 Photon energy / J 3,15E-19wavelength/nm 630,000
bandwidth/nm 0,005 telescope area / m^2 7,85E-03Telescope aperture/m 0,100 input power/W 8,59E+00
eff. focal length / m 1,800output power w/o bandwidth e/W 5,64E+00
boxwidth FOV/arcsec 2000,000
telescope transmission 6,56E-01Number of mirrors 0,000mirror reflectivity 0,900 image scale in arcsec/mm 1,15E+02
pixel scale in arcsec/pixel 5,73E-01 FOV / mm 1,75E+01
Number of lenses windows 4,000 Power within bandwidth/W 8,76E-06
lens transmission 0,900Number of photons within bandwidth / arcsec^2 /s 9,61E+06
Extra transmission 0,250
atmospheric transmission 0,800Number of photons within bandwidth / pixel /s 3,15E+06
exposure time/s 0,005
Pixel size / mm 0,005Number of photon electrons within bandwidth / pixel /s 2,21E+06
Quantum efficiency 0,700Number of photoelectrons 1,10E+04
SNR 1,05E+02
