Dark Energy Survey Filters

(April 22, 2005)

Draft Requirements on Dark Energy Survey (DES) filters

(NOTE: Not for construction)

Filters: SDSS g, r, i, z

Size: 633 mm outer diameter ±1 mm

Thickness: 15 mm

Requirement: ±.7 mm

Goal: ±.25 mm

Wedge:

Requirement: < 1 arcmin

Goal: < .35 arcmin

Minimum clear aperture: 593 mm

Environment: -7 to +27 C

Altitude: 0 to 2200 m (7220 feet), humidity to 98%

Angle of incidence: Beam incidence 0 to 4 degrees f/2.9 beam.

(Maximum ray angle: 12 degrees)

Half-power points (wavelengths in nanometers)

----- g ----- ----- r ----- ----- i ----- ----- z -----

DES 400. 550. 560. 710. 700. 850. 830. 1000.

*These are computed using logarithmically derived effective wavelength and

quoted FWHM. Wavelength-averaged is higher by 20-50 angstroms.

Bandpass errors: 5 nm (roughly, 1%).

Bandpass variation: Requirement: 5 nm; goal 2 nm peak-peak

Out of band blocking: < .1% of peak out to 1200 nm.

Transmission: Requirement 85% Goal 90% g, 95% r, 97% i, 97% z.

Wavefront errors will be measured over an aperture of 128 mm (beam diameter).