Field layout focal length Image size budget satisfied
Field layout & focal length ‘ • Image size budget satisfied within f 3° circle • View of secondary unobstructed with f 3. 2° circle • Annulus excellent for wavefront sensing, pupil imaging, etc. § 7. 1. 4. 4
Field Distortion • Distortion: <± 3% from mean scale • Science requirement presentation says <1% • Affects warping computation especially if high order terms are present • Klaus Hodapp is leading effort to reduce distortion amplitude and order • What is the requirement and goal? • What is “best shape”? § 7. 1. 4. 7
Antireflection coatings • • • Telescope bandpass: 400 to 1070 nm Common AR coatings • R(ave) < 1% • R(abs)< 1. 5% Filter AR coatings will be significantly better § 7. 1. 4. 9
Antireflection coatings ‘ § 7. 1. 4. 9
Photometric accuracy • Science Design Reference Mission • 0. 1 mag photometry • Exception: var / bright stars, 2 mmag relative photometry • Exceptional hardware not required - ref. Steve Howell § 7. 1. 6
Photometric accuracy Derived Requirements • Stray light • Fully baffled with tube, primary, secondary and conical baffles • Ghost images • Minimize number of lenses • Consider surface curvature and spacing in optical design • Treat surfaces with antireflective coatings • Diffraction • Mount secondary support vanes at different angles in each telescope? Is this desirable? Is it a requirement? How is it to be resolved? § 7. 1. 6
Image Size Budget • • “Since our goal is to build a telescope which degrades the incoming image as little as possible, it seems appropriate to specify the errors in the telescope so they correspond to the distortions already induced by the atmosphere. ” Optical Design, Error Budget and Specifications for the Columbus Project Telescope by J. M. Hill, Proceedings of SPIE conference on Advanced Technology Optical Telescopes IV, 1236, p. 86 (1990) and references cited therein. § 7. 1. 7
Structure function • • The structure function is f^2(x) = (l/2 p)^2*6. 88*(x/r )^(5/3). It is the RMS wavefront error of two points on the wavefront as a function of their separation. Straightforward to compute Examples • Finite element calculations of mirror support induced distortions • Optical shop profilometry or interferometry. 0 § 7. 1. 7
Structure function § 7. 1. 7
Image Size Budget § 7. 1. 7
Image Size Budget Primary Mirror § 7. 1. 7
Image Size Budget Alignment, focus, tracking § 7. 1. 7
Mount Control • Requirement set by efficiency considerations • Acquisition and settling time; 2 to 5 seconds for a 3° motion on the sky • t = 2*sqrt(d/a) • For d = 4°, a = 1°/s^2; t = 4 seconds • This corresponds to a 3° polar/az offset at 41° dec/alt • Time for 180° slew • Velocity limited • 2°/s yields 90 seconds • Occasionally, cable unwrap may require going the long way • Is modeling needed to refine requirements? • Some performance improvements may be possible § 7. 2. 9
Mount Control • Maximum tracking time • No requirement currently set, but propose 20 minutes. • For an alt-az telescope, this affects the range of motion of the instrument rotator and the azimuth axes. § 7. 2. 9
Filter Changer • Filter change time • Flows down from Design Reference Mission required number of changes per night and operational efficiency • Currently: TBD, about 2 minutes • Ok to adopt 2 minutes or is further analysis required? • Filter changer orientation • Filters may be changed in any orientation with respect to gravity § 10. 5
Pan-STARRS FILTERS Desiderata • We want the widest bandpasses possible • Make bands disjoint • We will have significant Y color terms • Avoid the 930 -960 nm absorption disaster • Saturated lines • Absorption not proportional to sec(z) • Spatially and time variable • Don’t go much longer than 1µm • Avoid a QE that is temperature sensitive. • Color terms between (within) CCDs § 10. 25
• The 50% transmission wavelengths vary by about 10 nm • The g and z short wavelength transitions are different • The g and r passband transmission varies by up to 20% • Stopband rejection is better than a part in 1000 http: //poi. ifa. hawaii. edu/private/documents/siegmund /Telescope/20030313_Filter. Comparison/index. html Mega. Cam v. SDSS § 10. 25
z Y • Median water vapor on Mauna Kea • 1. 65 mm (Jan-Jun) • 2. 98 mm (Jul-Dec) http: //www. gemini. edu/sciops/Obs. Process/ obs. Constraints/oc. Trans. Spectra. html Atmosphere Transmission § 10. 25
Burke-SDW 2002. pdf CCD Response Y • QE at 1. 25 µm strongly dependent on temperature • Y-band response will be shaped like a sawtooth • Down by x 4 from 960 to 1030 nm
Y 1 • Detector response not removed. Y http: //subarutelescope. org/Observing /Instruments/OHS/spec/skyspec. html Sky Spectrum - In. Sb § 10. 25
Y 1 http: //optik 2. mtk. nao. ac. jp/FOCAS/Users. Guide /Observing/Sky. Lines/OH_Spectrum. htm Sky Spectrum - Si • Detector response not removed. § 10. 25
g
r
i
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Y 1
Y 2
Pan-STARRS FILTERS Y band proposed resolution • Submit science cases to the science working group for decision. -Ken Chambers § 10. 25
SS Baseline § 10. 25. 1. 1
Pan-STARRS FILTERS SS band filter cutoffs • No scientific issues. The criterion is optimal asteroid detection. • Competing technical issues 1. Red cutoff blocks the worst of the sky OH emission. 2. Blue cutoff limits image spreading due to atmospheric differential refraction and telescope chromatic aberrations. 3. Filter needs to be wide as possible consistent with items 1 &2 § 10. 25. 1. 1
Pan-STARRS FILTERS SS Band • • Options… 1. Baseline: 520 nm to 820 nm. 2. Fallback: 560 nm to 870 nm. Resolution: Model detection threshold for asteroids given atmospheric seeing, diffraction and emission, Huygens PSF from Zemax, detector spectral response and asteroid SEDs. -Nick Kaiser and Rob Jedicke http: //pan-starrs. ifa. hawaii. edu/project/people/kaiser/filterdesign. pdf Moving Object Detection Roadmap v. 0 28 April 2003 (Jedicke) § 10. 25. 1. 1
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