The following tables list -- when possible -- the as-built physical, imaging, and spectroscopic characteristics of DEIMOS. In some instances (denoted by *) predicted values are listed in lieu of actual measurements.
Location | Right Nasmyth platform, Keck II; removable from focus |
Layout | Capacity for two cameras fed from common collimator; only one camera presently built |
Rotator | 732° rotation (-330° < ROTPPOSN < +402°) |
User access | Slit masks, all gratings and all filters |
Guiding system | One guider; 3.6×3.6 arcmin FOV; slit-viewing and offset modes are both available |
Spectrograph flexure control | Two-coordinate beam-steering with closed-loop feedback |
Flexure (uncorrected) |
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Flexure (corrected) | <0.5 px image in each axis |
Slit masks | 11 slots in cassette, with one spot reserved for dedicated
focusing mask and 10 available for observer use; cylindrical radius of curvature matched to focal plane curvature |
Slitlet options | Slitlets of arbitrary size and orientation |
Dispersive elements | 2 slots for 6×8 in gratings |
Imaging option | Silvered flat mirror replaces grating |
Filters1 | 6.25×6.25 in glass filters; 7 slots; BVRIZ, BAL12 (clear), GG400, GG455, GG495, OG550 |
Collimator focal length | 86.50 in |
Camera focal length | 15.00 in |
Beam diameter | 6.33 in for 10.95 m primary; 5.79 in for 10.02 m primary |
Monochromatic f/ratio | f/2.358 for 11.00 m primary; f/2.586 for 10.02 m primary |
Polychromatic f/ratio | f/1.29 |
Scale at detector | 0.00759 arcsec/µm; 0.1185 arcsec per 15µm px |
CCD detector array | 8192×8192 px (15 µm px); 2×4 mosaic of 2K×4K CCDs |
Angular field radius of camera | 11.40° |
Camera glass transmission* | 97% for lambda > 5200 Å; 88% at 3900 Å; 93% at 4400 Å |
Total camera throughput* | 85% at lambda > 5200 Å; 77% at 3900 Å (including coatings and transmission) |
Field shape | Rectangular with 2 lopped-off corners; sliver out of long side |
Outer dimensions of rectangular field | 16.7 arcmin×5.0 arcmin |
Area lost to CCD mosaic gaps | 0.4 arcmin×5.0 arcmin |
CCD pixel scale | 0.1185 arcsec per px (15µm px) |
Wavelength range (imaging) | 4000 Å - 10,500 Å |
Standard filters1 | BVRIZ + 2 user filters |
Throughput at 6000 Å2 | 40% (including telescope) |
Image size | sigma=1.1 px in center, 1.4px at edge |
Expected count rate3 | 800 e- per sec in V band at 21.0 mag |
Mode changes | 120-190 sec changeover between mirror and grating, depending on slider |
Total slit length | 16.7 arcmin |
Usable slit length1 | 16.3 arcmin |
Total number of slitlets | up to 130 slitlets with 1.5 arcsec gaps |
Tilted slits | up to 30° |
CCD detector scale | 0.1185 arcsec per px (15µm px) |
Wavelength range (spectra) | 4100 Å -- 11,000 Å |
Order blocking filters | BAL12 (clear), GG400, GG455, GG495, OG550 |
Slit widths | User selectable by choice of mask; long-slits will provide variety of fixed widths |
Design slit widths | 1.0 arcsec nominal, 0.5 arcsec good seeing |
Typical alignment accuracy | 0.1 arcsec in both spectral and spatial axes |
Current gratings (all 6×8 in) | 600 l/mm (7500 Å blaze; aluminized); 830 l/mm (8640 Å blaze; gold-coated); 900 l/mm (5500 Å blaze; aluminzed); 1200 l/mm (7500 Å blaze; gold-coated); |
Number of grating slots | 2 slots available |
Corresponding dispersions | 0.65 Å/px, 0.47 Å/px, 0.44 Å/px, and 0.33 Å/px |
Spectral lengths (8000 px) | 5300 Å, 3840 Å, 3530 Å, and 2630 Å |
FWHM resolutions | 3.5 Å, 2.5 Å, 2.1 Å, and 1.1-1.6 Å for 0.75 asec slit |
Throughput at 6000 Å2 | 29% (including telescope) |
Count rate at 6000 Å | 1.0 e- per sec at V = 21.0 |
Predicted S/N on faint stellar objects in one hour (low resolution)3 | 5 for V = 24.0; 12 for V = 23.0; 21 for V = 22.0 |
Achieved S/N on faint galaxies in one hour (high resolution)4 | 0.3-0.6 for R = 24.0; 0.6-1.2 for R = 23.0; 1.2-2.4 for R = 22.0; 2.2-4.6 for R = 21.0; |