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

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 K’s for the options above – Wide-field corrector options

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) Image quality improves as window & filter are allowed to move away from prime focus Question: What does this solution space look like? Telescope clamshell shutter option (not necessary, but available if it eases prime congestion)

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

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

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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

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

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

Thick window, flat filter option Surprisingly good image 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

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

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

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

System/Prescription Data File : C:\Users\Richard Dekany\Documents\COO\Projects\PTF2\Optical Design\v3_ztfc_12segmented_flattener_equiConcaveMonoAsphere Window_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 = Glass Catalogs : SCHOTT MISC Ray Aiming : Off Apodization : Uniform, factor = E+000 Temperature (C) : E+001 Pressure (ATM) : E+000 Adjust Index Data To Environment : Off Effective Focal Length : (in air at system temperature and pressure) Effective Focal Length : (in image space) Back Focal Length : Total Track : Image Space F/# : Paraxial Working F/# : Working F/# : Image Space NA : Object Space NA : 6.223e-008 Stop Radius : Paraxial Image Height : Paraxial Magnification : 0 Entrance Pupil Diameter : Entrance Pupil Position : 0 Exit Pupil Diameter : Exit Pupil Position : Field Type : Angle in degrees Maximum Radial Field : Primary Wavelength : µm Lens Units : Millimeters Angular Magnification : Fields : 5 Field Type : Angle in degrees # X-Value Y-Value Weight Wavelengths : 3 Units: µm # Value Weight SURFACE DATA SUMMARY: Surf Type Radius Thickness Glass Diameter Conic Comment OBJ STANDARD Infinity Infinity STO STANDARD LLF CORRECTOR 2 EVENASPH BK CORRECTOR 3 EVENASPH CORRECTOR 4 STANDARD Infinity STANDARD MIRROR M1 6 STANDARD Infinity STANDARD F_SILICA STANDARD Infinity EVENASPH F_SILICA STANDARD COORDBRK Marginal Focus 12 STANDARD F_SILICA STANDARD IMA STANDARD Infinity CCD Mosaic Surface 9 EVENASPH Coeff on r 2 : e-005 Coeff on r 4 : e-010 Coeff on r 6 : e-017

Similar 4-segment solution?

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

Side note: 4Ks vs. 10Ks…

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

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

Non-chorded solutions w/ aspheric correctors

Spherical meniscus filter Flat CCD mosaic Plano-convex dewar window Static aspheric corrector

Thick dewar window… Design FWHM = 1.6 arcsec – Availability of meniscus filter and aspheric corrector can’t make up for thick dewar window – So, rule out these options