The Modular Spectrograph is a moderate to high resolution spectrograph for use at the f/7.5 focus of either the 2.4-m Hiltner or the 1.3-m McGraw-Hill telescope. It is a second generation cousin of the Modular Spectrograph used on the duPont 2.5-m telescope of the Las Companas observatory.
It can be used either in a long slit mode or with aperture masks. The slit length is 50 mm (9.6 arc-minutes) long. Beware of slit curvature and the curved focal plane.
The collimator is a 429 mm f/4.3 UK50-fluorite cemented triplet designed by Jim McCarthy.
On the 2.4-m the approximate focus for direct imaging is about 170 units higher than the focus for this spectrograph.
There are two camera ports using commercial Cannon camera lenses: the short port has a 85 mm f/1.2 lens and the long port has a 200 mm f/2.8 lens. With a 15 micron pixel detector, these give scales of 0.850 arc-seconds per pixel and 0.365 arc-seconds per pixel respectively. These cameras suffer from signficant chromatic aberration: there is a sharp break in the focuscurves at 4861 Angstroms, making it virtually impossible to work on both sides of this peak. In general, the Modular is a 'red' spectrograph, although it may be possible to work in limited wavelength ranges blueward of 4861 Angstroms.
The following 102 x 102 mm plane reflection gratings are available:
|Grating||Blaze wavelength||Blaze angle|
|600 l/mm||5000 A||8.63 deg|
|830.8 l/mm||8465 A||20.57 deg|
|1200 l/mm||5000 A||17.45 deg|
There are two 3 inch square grisms available which mount immediately in front of the camera lenses. They may be used either as the primary dispersing element when used with a flat in the grating mount, or as a cross disperser when used with one of the above gratings.
|Grism||Blaze wavelength||Central Wavelength||Blaze angle|
|200 l/mm||6730 A||7000 A||15.0 deg|
|300 l/mm||5200 A||6500 A||17.45 deg|
A full set of order separating filters is available which mount in the post slit filter holder. A post slit eyepiece is available for knife edge focusing.
A complete manual for the spectrograph is kept in the control room.