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Some General Considerations on Wide Field Telescopes. Dirk Soltau Kiepenheuer-Institut für Sonnenphysik. 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
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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
Basic assumptionsandimmediateconclusions • Detectorsize: 4k x 4 k pixels, 5 µm pixelsize • Field ofview: 0.7° 2500 arcsec • pixelscale = 0.6 arcsec • imagescale = 120 arcsec/mm • focallength = 1720 mm Synoptic Network Workshop, Boulder 22.-24.4.2013
Diameter • resolutionaccordingtosamplingtheorem: 1.2 arcsec = 5.8 µrad • D = 1.22 λ / 5.8E-6 • minimum Diameter w.r.tresolution = 0.1 m Synoptic Network Workshop, Boulder 22.-24.4.2013
Bandwidth, SNR • Assumedbandwidth: 5 pm ( 50 mÅ, R = 100000 @ 500 nm) • AssumedExposure time: 0.005 s F Ret Cam1 PBS Sun Telescope Cam2 Synoptic Network Workshop, Boulder 22.-24.4.2013
Counts and SNR for 5 msexp. time Diameter shouldexceed 0,5 m f/# < f/3.5 Synoptic Network Workshop, Boulder 22.-24.4.2013
Mounting (commoninstrumentplatform) • May beweneed different instrumentsfor different SNR requirements (Polarimetry vs. imaging) • Severalinstruments on oneplatformmaybe a solution SOLIS Synoptic Network Workshop, Boulder 22.-24.4.2013
Image Motion and Noise 2 pixel 0.1 m 0.1 m 1 pixel 1 m 1 m Sun = 104isoplanaticpatches Averageseeinginducedimagemotionofthewholedisk will bearound 0.01 pixel
Time constant 1 m 0.1 m
Image motion: Effect on imagesubtraction - Example: shiftby 0.1 pixel 10-2noise = Image stabilizationneeded, dual beam polarimetrydesirable
Image stabilization? • Main causeprobably instrumental: • spatialdimensions: 1m 1 arcsec = 5 µm atthemirroredge • Limbsensor vs. Correlationtracker • Tiptiltmirror • relayoptics? • Solar Orbiter (PHI) concept? Synoptic Network Workshop, Boulder 22.-24.4.2013
Optical Design Options • Design drivingparameters: • Detector • SNR @ typicalexposure time Synoptic Network Workshop, Boulder 22.-24.4.2013
Refractor • Goodperformance, limited diameter Example: Chrotel (KIS) Synoptic Network Workshop, Boulder 22.-24.4.2013
Example: Maksutov D = 200 mm, FOV = 0.5 deg + Potential forevacuation - 10 µm Synoptic Network Workshop, Boulder 22.-24.4.2013
Example: Ritchey-Chretien Cassegrain D = 600 mm, FOV = 0.5 deg • Mightneed a fieldcorrectorif larger • needsbaffling (daylightblindness) Synoptic Network Workshop, Boulder 22.-24.4.2013
Consider different designsfor different purposes • Severaltelescopes on a commonstructure • SOLIS concept Titisee
Summary • Basic requirement: SNR • Image stabilization – ifnecessary – has large impact on the design • Diameter not determinedbyresolutionarguments telescopedoesn‘tneedtobediffraction limited • Evacuationshouldbeconsidered (catadioptricsystem?) • Multiple telescopeplatformmightbeuseful • Ritchey-Chretien promising. But falselightcountermeasuresnecessary Synoptic Network Workshop, Boulder 22.-24.4.2013
Photon electrons Synoptic Network Workshop, Boulder 22.-24.4.2013