Filters are located on the filter wheel which lies in the parallel beam (after the collimator). Up to 11 filters can be mounted on the wheel. Of these, one should be a Free position which is necessary for spectroscopy.

In principle, filters should not, and in fact most do not, change the focus of the instrument. Some of the Stromgren and interference filters may necessitate a refocus.

The filter wheel is located at a relatively large distance from the focal plane and so filter defects have a considerable effect on the image quality. Observers should keep this in mind while bringing their own filters.

The maximum dimension which can be accommodated on the filter wheel is a diameter of 60mm and thickness of 10mm. Please note that the filter and the grism wheels are located very close to each other and so there is very little possibility of squeezing in larger filters.

The basic EFOSC2 filter set is listed below. The entire filter set for La Silla may be obtained by invoking in ESO-MIDAS

>create/gui filters

The La Silla filter database can also be queried at the following URL: 

http://filters.ls.eso.org/

Many (but not all) of these can be mounted on the EFOSC2 filter wheel. In particular you should look for filters with 60mm diameter.

Users who either wish to use one of the filters not in the basic EFOSC2 list (either an ESO filter or one of their own) should contact the telescope support team well in advance of their run to make sure that their needs can be met.

The EFOSC2 Basic Set

¹ In some of the graphs they are labelled SUSI, but in fact the curves are instrument independent.