EUROPEAN SOUTHERN OBSERVATORY




Each of the two imaging filter wheels has 9 positions of which 8 are available for mounting filters and one is kept free. Ordersorting filters are also placed into these filter wheels. Both red and blue filters have a free circular diameter of 80 mm and an outside diameter of 85 mm. Adapters are available for filters of other instruments (e.g. EFOSC, DFOSC) but use of these, smaller filters will produce vignetted images only useful in the center of the CCD. Adapters have to be requested a few weeks in advance.
The red filter wheel is placed in the parallel beam and therefore suffers from reflections between the CCD and the filter. To avoid this, most filters are mounted at angles of 5 degrees inclination, and the remainder at 2.5 or 7.5 degrees. Blue arm filters, used in the converging beam in front of the blue camera, do not have this problem and hence are mounted with no inclination. Using a redarm filter in the blue will result in a slight change of the central wavelength and will cause some astigmatism. If a blue filter is used in the red arm, every object in the field produces a reflection ghost, which is about 5 magnitudes fainter than the original object. Thus, although it is possible to use blue filters in the red and viceversa (one might want to do this in the overlap region, 400 to 500 nm), filters should normally be used in the wheel they are intended for.
Filters with very narrow bandwidths are not well suitable for the red arm. Because the filters are mounted in the parallel beam, the central wavelength will change across the field. In extreme cases, the central wavelength may be outside the edge of the filter sensitivity response near the edge of the field of view. The tabulated wavelength corresponds to the center of the CCD. The wavelength change also affects the image quality across the field.
Transmission curves are available in the table below as GIFs, PostScripts and
ASCII tables.
ESO  Filter  wavelength (nm)  width (FWHM)  Peak efficiency %  Cell type  Files  Preview 

EMMI Red arm  
Broadband filters  
605  Bb  413.9  109.8  68  R3  PSdat  
606  V  542.6  104.4  87  R3  PSdat  
608  R  641.0  154.2  80  R3  PSdat  
610  I  798.5  155.2  94  R3  PSdat  
611  Z  >843.4  lwp  88  R3  PSdat  
772  Gunn g  509.4  75.1  87  R2  PSdat  
773  Gunn r  676.4  80.9  85  R3  PSdat  
774  Gunn i  806.0  142.3  94  R2  PSdat  
775  Gunn z  997.3  52.2  97  R  PSdat  
776  Tyson B  445.6  146.2  87  R  PSdat  
Narrowband filters  
587  He I  448.0  4.8  53  R1  PSdat  
652  He II  469.3  7.3  62  R1  PSdat  
672  Spec.  472.2  28.6  79  R1  PSdat  
771  H Beta cont.  477.5  7.4  81  R  PSdat  
770  H Beta  486.2  7.8  77  R3  PSdat  
765  Spec.  489.5  14.9  79  R2  PSdat  
673  Spec.  502.8  2.66  77  R1  PSdat  
766  Spec.  505.9  21.2  83  R2  PSdat  
589  O III / 0  501.1  5.5  61  R2  PSdat  
590  O III / 3000  505.6  6.2  50  R2  PSdat  
591  O III / 6000  511.1  6.1  69  R2  PSdat  
592 

515.6  6.4  67  R2  PSdat  
593  O III / 12000  520.8  6.7  63  R3  PSdat  
594  O III / 15000  525.7  6.8  66  R3  PSdat  
767  Spec.  546.4  20.7  75  R2  PSdat  
768  Spec.  602.6  53.8  92  R2  PSdat  
654  H Alpha  656.0  3.3  36  R3  PSdat  
596  H Alpha / 0  656.8  7.3  54  R3  PSdat  
597  H Alpha / 3000  663.1  6.6  60  R3  PSdat  
598  H Alpha / 6000  668.5  6.7  55  R3  PSdat  
599  H Alpha / 9000  676.0  7.1  51  R3  PSdat  
600  H Alpha / 12000  683.3  7.2  55  R3  PSdat  
601  H Alpha / 15000  689.4  7.3  58  R3  PSdat  
653  N II / 0  658.8  3.0  56  R2  PSdat  
595  N II / 0  660.7  7.1  55  R3  PSdat  
655  S II / 0  672.8  7.5  53  R3  PSdat  
656  Spec.  912.9  19.3  89  R3  PSdat  
657  S III / 0  954.0  10.5  89  R2  PSdat  
795  Spec  435.9  93.1  80  R2  PSdat  
796  Spec  539.8  95.7  89  R2  PSdat  
Ordersorting filters  
643  BG38 2mm  481.9  276.9  96  R2  PSdat  
645  OG530 3mm  >530.0  lwp  95  R1  PSdat  
646  RG715 3mm  >721.5  lwp  98  R3  PSdat  
769  BG39  472.2  237.2  86  R3  PSdat  
EMMI Blue arm  
602  U Bessel  354.2  54.2  67  B  PSdat  
603  B Bessel  422.3  94.1  66  B  PSdat  
658  EUV (UG11/5)  <366.1  swp  70  B  PSdat  
647  Ne V  342.2  8.3  39  B  PSdat  
648  O II / 0  372.5  6.9  35  B  PSdat  
649  O II / 5000  379.5  6.7  44  B  PSdat  
650  O II / 10000  385.3  7.0  43  B  PSdat  
651  O II / 15000  392.7  7.8  41  B  PSdat  
671  He II  468.0  15.2  57  B  PSdat  
588  He II  469.0  6.6  71  B  PSdat  
723  Spec.  394.9  3.5  44  R  PSdat  
644  GG375 3mm  >369.2  lwp  99  B  PSdat 