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Some General Considerations on Wide Field Telescopes

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

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  1. Some General Considerations on Wide Field Telescopes Dirk Soltau Kiepenheuer-Institut für Sonnenphysik Synoptic Network Workshop, Boulder 22.-24.4.2013

  2. 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

  3. 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

  4. Bandwidth, SNR • Assumedbandwidth: 0.005 nm ( 50 mÅ) • AssumedExposure time: 0.005 s F Ret Cam1 PBS Sun Telescope Synoptic Network Workshop, Boulder 22.-24.4.2013 Cam2

  5. Counts and SNR Diameter shouldexceed 0,5 m  f/# < f/3.5 Synoptic Network Workshop, Boulder 22.-24.4.2013

  6. Mounting (commoninstrumentplatform) • May beweneed different instrumentsfor different SNR requirements (Polarimetry vs. imaging) •  Severalinstruments on oneplatformmaybe a solution Synoptic Network Workshop, Boulder 22.-24.4.2013

  7. 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

  8. Time constant 1 m 0.1 m Synoptic Network Workshop, Boulder 22.-24.4.2013

  9. Image motion: Effect on imagesubtraction - Example: shiftby 0.1 pixel 10-2noise =  Image stabilizationneeded, dual beam polarimetrydesirable Synoptic Network Workshop, Boulder 22.-24.4.2013

  10. Image stabilization? • Main causeprobably instrumental: • spatialdimensions: 1m  1 arcseccorresp. 5 µm • Limbsensor vs. Correlationtracker • Tiptiltmirror • relayoptics? • Solar Orbiter (PHI) concept? Synoptic Network Workshop, Boulder 22.-24.4.2013

  11. Optical Design Options • Design drivingparameters: • Detector • SNR @ typicalexposure time Synoptic Network Workshop, Boulder 22.-24.4.2013

  12. Refractor • Goodperformance, limited diameter Example: Chrotel (KIS) Synoptic Network Workshop, Boulder 22.-24.4.2013

  13. Example: Maksutov D = 200 mm, FOV = 0.5 deg + Potential forevacuation - 10 µm Synoptic Network Workshop, Boulder 22.-24.4.2013

  14. 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

  15. Summary • Basic requirement: SNR • Image stabilization – ifnecessary – has large impact on the design • Diameter not determinedbyresolutionarguments telescopedoesn‘tneedtobediffraction limited • Evacuationshouldbeconsidered (catadioptricsystem?) • Ritchey-Chretien promising. But falselightcountermeasuresnecessary Synoptic Network Workshop, Boulder 22.-24.4.2013

  16. Photon electrons Synoptic Network Workshop, Boulder 22.-24.4.2013

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