There are two available grisms in the reimaged/spectrograph mode: 300 l/mm and 600 l/mm. There is no available tilt for the grisms, so the wavelength coverage for the standard longslits is fixed. See Table 6 for a description of the grisms.
It is possible to obtain a different center wavelength by constructing a longslit (or multislit) mask that is offset in the focal plane along the dispersion direction. See the section on making multislit masks for a description of how to do this.
Interference filters are best placed in a parallel beam, so that their appropriate place in this instrument is in the grism wheel. Judy Cohen has a filter holder for the grism wheel; see her to use it. The clearance at the top of the filter holder is small, so it requires shaving off the top of the screws.
| Table 6 Grism Wheel |
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| Position | Grism (l/mm) |
Blaze (Å) |
Center Wavelength (Å) |
Mean Dispersion (Å pixel-1) |
| 1 | 300 | 5500 | 6500 | ~3.1 |
| 2 | clear, available | |||
| 3 | 600 | 4800 | 5000 | ~1.46 |
| 4 | as of 2004 in use | H-alpha | filter | |