Both grating and camera angles are remotely adjustable.
The blaze (peak grating efficiency) wavelength can be altered by
slightly changing the grating angle.
The wavelength coverage on the detector is determined primarily by the
camera angle, with weaker dependence on the grating angle.
slit curvature, the wavelength coverage, dispersion and resolution all
vary between central and outer fibres. The dispersion also increases
with wavelength; the dimensionless resolution (l/dl) increases more
strongly with wavelength.
Most of the gratings are deliberately `slanted', meaning that the
fringes are tilted within the grating (like a venetian blind). The
reason is to avoid a 0th-order ghost that would otherwise lie in the
middle of the detector when used in Littrow.
Spectrograph numbers: camera focal length is 247mm. Demagnification is
0.413 . Allowed grating angles are 0-49° ; allowed camera angles are
0-94.3° (blue arm) or 0-95.3° (red arm) . There are 2048
spectral x 4096 spatial 15um pixels. Dichroic
crossover wavelength is 5700Å .