ZTFC 12-segment field flattener (and related) options

1. ZTFC 12-segment field flattener (and related) options R. Dekany 07 Aug 2012

2. ZTF Camera • Goal from last discussion was a practical design that covers 12 wafer-scale CCD’s with FWHM ≤ 1.1 arcsec for each band • Avenues identified as promising • Chorded CCD positioning (along best-fit sphere) • To mitigate field curvature driving down flattener thickness • Segmented field flattener / segmented dewar window • 32 4K’s vs. 12 10K’s for the options above • Wide-field corrector options

3. Consider the class of solutions: 12 chorded CCDs, each with its own thin field flattener Global meniscus dewar window w/ 1 aspheric surface Meniscus filter (exchangeable) Telescope clamshell shutter option (not necessary, but available if it eases prime congestion) Image quality improves as window & filter are allowed to move away from prime focus Question: What does this solution space look like?

4. Quincunx field pts for each CCD 1 field flattener per CCD 12 CCDs on chorded mount Aspheric dewar window (design also allows for segmented dewar window strategies) Meniscus filter (exchangeable) Prime focus obscuration Max Distance Constraint

5. Equal areal weight optimization (Outer CCD weight = 2x Inner)

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9. Conclusions for this class of solution… • Depending on remainder of error budget, allocation of 1.1 arcsec to design FWHM seems about right • To exploit good seeing, allow filter vertex to center of FPA distance of ~ 210mm • Implies meniscus filter diameter ~ 520 mm (20.5 inch) • Near-term to do: • Optimize filter glass choice for g’ and R spectral bands • Worry about coating the meniscus filters for uniform bandwidth and transmission • Worry about handling / exchanger

10. Flat CCD, thick dewar window, flat filter, plus corrector (A more classical option…)

11. 4 deg max field angle Biconvex dewar window Flat CCD focal plane Aspheric corrector Meniscus corrector (640mm diam.) Flat filter (exchangeable) Prime focus obscuration

12. Thick window, flat filter option • Surprisingly goodimage quality • FHWM ~ 1.0” • Lots of glass • Low transmission • Ghosting? • Not verified for R’(though probably ok) • Large element • Probably can’t reduce it much before harming DIQ

13. Equiconcave aspheric window + Plano-convex filter (A minimal optics solution…?)

14. Quincunx field pts for each CCD 1 field flattener per CCD 12 CCDs on chorded mount Fused silica aspheric dewar window (equiconcave) Plano-convex filter (exchangeable) Prime focus obscuration

15. Equiconcave aspheric window + Plano-convex filter • Field-averagedFWHM = 1.12” • Comfortable cryostat window • All fused silica • One plano filter surface • Easier coating? • 542 mm diam. • Other concerns • ‘Contact lens’ ghosts…

16. Fields : 5 Field Type : Angle in degrees # X-Value Y-Value Weight 1 0.000000 0.000000 1.000000 2 0.000000 1.789000 1.000000 3 1.789000 1.789000 1.000000 4 0.894500 0.894500 2.000000 5 1.789000 0.000000 1.000000 Wavelengths : 3 Units: µm # Value Weight 1 0.536000 0.850000 2 0.467000 0.900000 3 0.616000 0.850000 SURFACE DATA SUMMARY: Surf Type Radius Thickness Glass Diameter Conic Comment OBJ STANDARD Infinity Infinity STO STANDARD 117054.9 11.481 LLF6 1244.6 0 CORRECTOR 2 EVENASPH 64570.28 17.2206 BK7 1260 0 CORRECTOR 3 EVENASPH 173900.9 2751.5 1260 0 CORRECTOR 4 STANDARD Infinity 3351.5 1260 0 5 STANDARD -6123.94 -2700 MIRROR 1782.416 0 M1 6 STANDARD Infinity -140.5651 449.6796 0 7 STANDARD -2985.008 -18.06109 F_SILICA 375.5883 0 8 STANDARD Infinity -109.3336 370.9474 0 9 EVENASPH 2168.138 -15.84882 F_SILICA 311.0921 0 10 STANDARD -2168.138 -67.32618 302.268 0 11 COORDBRK - 0 - - Marginal Focus 12 STANDARD -963.5794 -6.01121 F_SILICA 137.6897 0 13 STANDARD 2251.796 -1.649183 137.6897 0 IMA STANDARD Infinity 135.7214 0 CCD Mosaic Surface 9 EVENASPH Coeff on r 2 : -4.2364504e-005 Coeff on r 4 : -1.9236429e-010 Coeff on r 6 : -6.9743573e-017 System/Prescription Data File : C:\Users\Richard Dekany\Documents\COO\Projects\PTF2\Optical Design\v3_ztfc_12segmented_flattener_equiConcaveMonoAsphereWindow_planoConvexFilter_215mm_nice_compromise.ZMX Title: ZTFC Date : 8/7/2012 Configuration 1 of 2 GENERAL LENS DATA: Surfaces : 14 Stop : 1 System Aperture : Entrance Pupil Diameter = 1244.6 Glass Catalogs : SCHOTT MISC Ray Aiming : Off Apodization : Uniform, factor = 0.00000E+000 Temperature (C) : 2.00000E+001 Pressure (ATM) : 1.00000E+000 Adjust Index Data To Environment : Off Effective Focal Length : 3060.123 (in air at system temperature and pressure) Effective Focal Length : 3060.123 (in image space) Back Focal Length : 2.810671 Total Track : 6131.702 Image Space F/# : 2.45872 Paraxial Working F/# : 2.45872 Working F/# : 2.453778 Image Space NA : 0.1992791 Object Space NA : 6.223e-008 Stop Radius : 622.3 Paraxial Image Height : 135.2147 Paraxial Magnification : 0 Entrance Pupil Diameter : 1244.6 Entrance Pupil Position : 0 Exit Pupil Diameter : 516.0726 Exit Pupil Position : -1260.556 Field Type : Angle in degrees Maximum Radial Field : 2.530028 Primary Wavelength : 0.536 µm Lens Units : Millimeters Angular Magnification : 2.404811

17. Similar 4-segment solution?

19. Solution doesn’t work as well for 4-segment flattener • Design FWHM ~ 2.0”

20. Side note: 4Ks vs. 10Ks…

21. Quincunx field pts for each CCD 1 field flattener per CCD 32 CCDs on chorded mount Fused silica aspheric (plano) dewar window Plano-convex filter (exchangeable) Prime focus obscuration

22. Interesting compromise • Field-averagedFWHM = 1.07” • Two ‘Naturally’ plano surfaces • But… • 4K ROM’s coming in higher than 10K’s so CCD cost rules out this option