ZTF Field Flattener Rev 3

# ZTF Field Flattener Rev 3

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## ZTF Field Flattener Rev 3

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1. ZTF Field FlattenerRev 3 P. Jelinsky 2012/07/20

2. Window Thickness • The stress on a window, σ is • Where ν is the Poisson’s ratio, q is the pressure on the window, d is the window diameter and t is the window thickness • To first order the allowed stress is independent of the window diameter • Therefore the diameter to thickness ratio must be less than a given value. • Our mechanical engineer did an analysis and came up with a ratio of 10 (might need to be less at diameter grows) • The QUEST and PTF camera window has a ratio of 14.4 • The window thickness strongly affects the performance of the lens

3. Assumptions • Distance from flattener to CCD is >= 3mm • Allow distance from corrector to mirror to vary • d/t <= 14.4 (same as QUEST camera) • Flattener is Fused Silica • All spherical surfaces • Aspheric surfaces did not change performance much • Optimize over 5 wavelengths in the g’, r’ bands as below (allowing a focus change). • Report results for u’ and i’ band (allowing a focus change) • u’ band seems very narrow (Maybe I read DIQ spreadsheet incorrectly?) • Optimize over 5 field points, weighted by area

4. Focal Plane Layout • 9 detector focal plane needs a flattener with a radius of 3.8°, a 12 detector focal plane needs a flattener to a radius of 4°, a 16 detector focal plane needs a window to 5° • If field flattener is circular

5. Layout • No filter added yet

6. Case I Classical Schmidt • About 0.5 arcseconds FWHM for 4 ° radius • About 0.7 arcseconds FWHM for 5 ° radius • Only changed focus between bands 0.8 0.67 0.53 Average FWHM arcseconds 0.4 0.27 0.13

7. Case I Classical Schmidt (cont)

8. Case II Curved FP with lens (D/t = 14.4) • About 1.3 arcseconds FWHM for 4 ° radius • About 1.5 arcseconds FWHM for 5 ° radius • Only changed focus between bands 1.7 1.3 1.0 Average FWHM arcseconds 0.7 0.3

9. Case II Curved FP with lens (D/t = 14.4) (cont)

10. Case IIa Curved FP with lens (D/t = 25) • About 0.9 arcseconds FWHM for 4 ° radius • About 1.2 arcseconds FWHM for 5 ° radius • Only changed focus between bands 1.3 1.1 0.8 Average FWHM arcseconds 0.5 0.3

11. Case IIa Curved FP with lens (D/t = 25) (cont)

12. Case III Flat FP single lens (D/T = 14.4) • About 1.3 arcsecond FWHM for 4° radius • About 1.8 arcsecond for 5 ° radius • Only focus changed between bands 2 Average FWHM arcseconds 1

13. Case III Flat FP single lens (D/T = 14.4) (cont)

14. Case IV split flat FP (D/T = 14.4) • About 1.2 arcsecond FWHM for 4° radius • About 1.8 arcsecond for 5 ° radius • Only focus changed between bands 2 1 Average FWHM arcseconds

15. Case IV split flat FP (D/T = 14.4) (cont)

16. Case V 4 segment (16 CCD) FP (D/T = 14.4) • Each quadrant is flat but tilted • Forms the peak of a 4 sided pyramid • Each Quadrant has a vacuum field flattener in front • 16 total detectors

17. Case V (cont) R Band Imaging over ¼ of field

18. Case V (cont)

19. Summary • The 4 segment focal plane performs as well as a curved focal plane with a vacuum lens 1.67 1.33 1.00 Average FWHM arcseconds 0.67 0.33