The Walter Baade Telescope is the first of the twin 6.5 meter Magellan telescopes to be completed. The two telescopes are located 60 meters apart on an isolated peak (Cerro Manqui) at the Las Campanas Observatory. The telescopes are an alt-azimuth design. The principal foci are f/11 at the two Nasmyth locations and f/15 in the Cassegrain position, although at present only the f/11 focus is implemented on the Baade Telescope. In addition, three auxiliary f/11 are provided on the center section. An ADC corrector will be available for f/11 use to provide unvignetted fields up to 24 arcmin. Platforms on either side provide access to the instruments at the principal Nasmyth ports.
The Magellan primary mirrors were cast and polished by the Steward Observatory Mirror Lab. The mirrors are made of borosilicate glass with a lightweight honeycomb structure.
The f/11 focus is a Gregorian configuration, which was selected in order to optimize the performance of the collimator optics in the wide-field spectrograph (IMACS) currently under construction. The Gregorian secondary is also considerably less aspheric than the corresponding Cassegrain secondary, and is easier to test.
Active controls are incorporated in the telescope optics. The mirrors have position control for alignment. These are active during observing. Figure control of the primary mirror is used to correct low-order aberrations in the optical system. In addition, the secondary mirror has a tip-tilt mechanism for fast guiding.
Full information on the active optics system at Magellan can be found here
2. Optical Design
Each of the f/11 foci can be configured for wide-field use by inserting a corrector in the beam. The corrector includes atmospheric dispersion compensation (ADC). Use of the corrector shifts the optimum focal surface approximately 115 mm towards the tertiary mirror.
The following sections give the optical specifications.
2.1 Primary Mirror
|Focal Length:||8,128.0 mm|
|Focal ratio (ref.):||1.25|
|Entrance stop distance above primary vertex:||325 mm|
|Entrance stop diameter:||6,478.4 mm|
|Final focal ratio:||f/11.0|
|Nominal corrected field of view:||6 arcmin|
|Unvignetted field of view:||24 arcmin|
|Central obscuration (area):||7.4%|
|Secondary mirror coating:||Bare Aluminum|
|Focal length:||71,526 mm|
|Focal surface curvature (concave away from M2):||1,519 mm|
|Distortion at 3 arcminute field angle (at 500 nm):||0.005%|
|Final focal ratio:||f/10.97|
|Unvignetted/corrected field of view:||24 arcmin|
|Vignetting @ 15 arcmin field angle:||9%|
|Central obstruction (area):||7.4%|
|ADC cut-off (50% transmission):||330 nm|
|Focal length:||71,089 mm|
|Focal surface curvature (concave away from M2):||1,231 mm|
|Distortion at 12 arcminute field angle (at 500 nm):||0.12%|
The following is a tiny selection of available papers related to the construction and operation of the Magellan Telescopes: