General Design Considerations on Wide Field Telescopes

Dirk SoltauKiepenheuer-Institut fr SonnenphysikSynoptic Network Workshop, Boulder 22.-24.4.20131Some General Considerations on Wide Field TelescopesBasic assumptions and immediate conclusionsSynoptic Network Workshop, Boulder 22.-24.4.20132Detector size: 4k x 4 k pixels, 5 m pixel sizeField of view: 0.7 2500 arcsec

pixelscale = 0.6 arcsec image scale = 120 arcsec/mm focal length = 1720 mm

DiameterSynoptic Network Workshop, Boulder 22.-24.4.20133 resolution according to sampling theorem: 1.2 arcsec = 5.8 rad D = 1.22 / 5.8E-6 minimum Diameter w.r.t resolution = 0.1 m

Bandwidth, SNRSynoptic Network Workshop, Boulder 22.-24.4.20134Assumed bandwidth: 0.005 nm ( 50 m)Assumed Exposure time: 0.005 s

TelescopePBSCam1Cam2FRetSunCounts and SNRSynoptic Network Workshop, Boulder 22.-24.4.20135Aperturewavelength = 5 pmHeat loadPhotoelectronsSNR0.1 m400 nm10 W4500700.5 m400 nm200 W1100003501.0 m400 nm1000 W4500006700.1 m630 nm10 W90001000.5 m630 nm200 W2300004801.0 m630 nm1000 W900000950Diameter should exceed 0,5 m f/# < f/3.5Mounting (common instrument platform)Synoptic Network Workshop, Boulder 22.-24.4.20136May be we need different instruments for different SNR requirements (Polarimetry vs. imaging) Several instruments on one platform may be a solutionImage Motion and Noise7

0.1 m0.1 m1 m1 mSun = 104 isoplanatic patches Average seeing induced image motion of the whole disk will be around 0.01 pixel2 pixel1 pixelTime constantSynoptic Network Workshop, Boulder 22.-24.4.20138

0.1 m1 mImage motion: Effect on image subtractionSynoptic Network Workshop, Boulder 22.-24.4.20139

=-

Image stabilization needed, dual beam polarimetry desirableExample: shift by 0.1 pixel 10-2 noise

Image stabilization?Synoptic Network Workshop, Boulder 22.-24.4.201310Main cause probably instrumental:spatial dimensions: 1m 1 arcsec corresp. 5 mLimb sensor vs. Correlation trackerTiptilt mirrorrelay optics?Solar Orbiter (PHI) concept?

Optical Design OptionsSynoptic Network Workshop, Boulder 22.-24.4.201311Design driving parameters:DetectorSNR @ typical exposure time

RefractorSynoptic Network Workshop, Boulder 22.-24.4.201312Good performance, limited diameter

Example: Chrotel (KIS)

Example: MaksutovSynoptic Network Workshop, Boulder 22.-24.4.201313

+ Potential for evacuation- D = 200 mm, FOV = 0.5 deg10 mExample: Ritchey-Chretien CassegrainSynoptic Network Workshop, Boulder 22.-24.4.201314

D = 600 mm, FOV = 0.5 degMight need a field corrector if largerneeds baffling (daylight blindness)SummarySynoptic Network Workshop, Boulder 22.-24.4.201315Basic requirement: SNRImage stabilization if necessary has large impact on the designDiameter not determined by resolution arguments telescope doesnt need to be diffraction limitedEvacuation should be considered (catadioptric system?)Ritchey-Chretien promising. But false light counter measures necessaryPhoton electronsSynoptic Network Workshop, Boulder 22.-24.4.201316Solar Spectral Irradiance from ASTM data in W/^m^2/nm1,700Photon energy / J3,15E-19wavelength/nm630,000bandwidth/nm0,005telescope area / m^27,85E-03Telescope aperture/m0,100input power/W8,59E+00eff. focal length / m1,800output power w/o bandwidth e/W5,64E+00boxwidth FOV/arcsec2000,000telescope transmission6,56E-01Number of mirrors0,000mirror reflectivity0,900image scale in arcsec/mm1,15E+02pixel scale in arcsec/pixel5,73E-01 FOV / mm1,75E+01Number of lenses windows4,000Power within bandwidth/W8,76E-06lens transmission0,900Number of photons within bandwidth / arcsec^2 /s9,61E+06Extra transmission0,250atmospheric transmission0,800Number of photons within bandwidth / pixel /s3,15E+06exposure time/s0,005Pixel size / mm0,005Number of photon electrons within bandwidth / pixel /s2,21E+06Quantum efficiency0,700Number of photoelectrons1,10E+04SNR1,05E+02