[ ESO ] La Silla

The ESO 1.52-m Telescope
B&C Spectrograph

The Gratings A quick guide to choose
your grating
The B&C Overall
Tools The detector

General Information

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:

B&C Optical Parameters
Slit Scale
Collimator Focus Length
Grating Conf. Angle
Camera Foc. Length
Transversal Magn. Factor Detector
14.9 9.2 8.3 750 49 127 0.169 CCD#38

Technical Documentation

[*]The B&C Operating Manual and Cookbook
[*]Technical Reports
[*]Memos, Notes and Utilities for observers (Fe-He-Ar tables here) .

The Gratings

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.

A quick guide to choose your grating

See which is the grating with the greatest efficiency in the spectral range of your interest and with the dispersion you need:

0.047-0.066 nm/pxl
0.09-0.10 nmm/pxl Also include new grating #33
0.13-0.14 nm/pxl
0.19-0.20 nm/pxl Also include new grating #34
0.25-0.29 nm/pxl
0.37-0.38 nm/pxl
0.49-0.73 nm/pxl

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.

The B&C Overall Efficiency

Here are the B&C overall efficiency curves. They come from the combination of the efficiencies of the telescope, the spectrograph, the grating and the detector. They also account for the atmospheric extinction and the obstruction of the secondary mirror. In other words the efficiencies shown in the curves are the ratio between the number of detected photons divided by the number of incident photons on the primary mirror area.


[*] Efficiency curves This program can be useful to find the gratings that you need for your scientific program
[*] Exposure meter S/N v exposure time plots and table for the offered gratings
[*] Central wavelength Choose a grating and a grating angle and find the central wavelength, dispersion, slit width and other useful quantities you may need.
[*] Grating angle Choose a grating and a wevelength range and find the grating angle, dispersion, slit width and other useful quantities you may need.

[*] Spectrophotometric standards list (this is just a link to an ESO web page)

The Detector

The detector presently intalled at the B&C is a Loral Lesser CCD. Its ESO number is CCD#38. Here is link to our CCD#38 web-page.

Set-Up Forms

Remember: you must submit a set-up form before 7:00AM of the day you will start your observations (contact the Support astronomer if you need help, tel. 4217 or 4218 or beeper 93-12). If you arrive the same day you will start observing, you can submit such request using the web-based Remedy interface accessible from here or from the La Silla web page.
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