The ESO 1.52-m Telescope
| General |
|The Gratings|| A quick guide to choose |
| The B&C Overall |
The Boller & Chivens spectrograph at the ESO 1.52m has been equipped with a special dioptric camera for use with the f/15 Cassegrin focus (see the B&C Optical Configuration).
An order blocking filter assembly is located below the slit jaws to prevent overlapping of unwanted spectral orders. It may hold up to four filters. The correct filter choice is normally determined by the optical group and installed before an observing run. No deckers are used for observation.
The opto-mechanical configuration allows for a fixed angle between the incident and diffracted beam axis of the grating (configuration angle). The grating is mounted in an adjustable rotating cell that permits the choice of the central wavelength and spectral orders (grating angle).
The dioptric camera presently installed has an efficiency of ~87% between 430 nm and 900 nm and > 78% for wavelengths < 430 nm.
The slit assembly consists of two 64mm long polished and aluminized jaws on which the field of view can be seen by the guiding camera. The slit-width is remotely controlled from the observing console in the control room. Note that the slit width appears smaller to the detector than it actually is (called projected slit-width). This is due to the transversal magnification factor (the ratio of the camera to collimator focal lengths), and to the grating anamorphism (see the B&C Operating Manual).
The slit length is 4.5 arcmin and the scale in the spatial direction is 0.82 arcsec/px.
The new optical parameters, resulting from this camera are listed below:
|Collimator Focus Length|
|Grating Conf. Angle|
|Camera Foc. Length|
|Transversal Magn. Factor||Detector|
The number of gratings now offered at the B&C has been reduced with respect to the past in order to avoid duplication and to enable us to keep better track of the performances. The gratings have been selected according to the efficiency and to surface quality as reported by the optics team. Go here, to choose from the actually offered gratings.Anyway, for your information, in this list we report the features of 13 gratings which cover all the configurations available now and before.
See which is the grating with the greatest efficiency in the spectral range of your interest and with the dispersion you need:
0.09-0.10 nmm/pxl Also include new grating #33
0.19-0.20 nm/pxl Also include new grating #34
If you need more, try using the Efficiency curves program (which is among the tool programs).
Plots of the Schott glasses used for order sorting filters can be found here.