HIRES has two 12 position filter wheels that reside immediately behind the decker plate. Their primary function is to block unwanted orders from the cross-disperser. Each filter wheel has a "clear" position that is empty. Proper choice of blocking filters is critical for isolating particular regions of interest. The Table below gives some useful combinations of filter choice for given spectral regions. Note that each combination of filters requires refocusing of the collimator which is handled automatically if installed from the XHIRES GUI.
| Cross-disperser Order | Wavelength (microns) | Filter Wheel 1 | Filter Wheel 2 |
|---|---|---|---|
| 1 | 0.69 - 1.1 | 2 (OG610) | 1 (clear) |
| 1 | 0.63 - 0.95 | 3 (OG530) | 1 (clear) |
| 1 | 0.58 - 0.90 | 3 (OG530) | 1 (clear) |
| 1 | 0.53 - 0.85 | 4 (GG475) | 1 (clear) |
| 1 | 0.48 - 0.80 | 5 (KV418) | 1 (clear) |
| 1 | 0.44 - 0.75 | 6 (KV408) | 1 (clear) |
| 1 | 0.39 - 0.70 | 8 (KV380) | 1 (clear) |
| 1 | 0.35 - 0.65 | 9 (KV370) | 1 (clear) |
| 1 | 0.30 - 0.60 | 11 (WG335) | 1 (clear) |