EUROPEAN SOUTHERN OBSERVATORY

La Silla Science Operations: NTT

EMMI Filters

EMMI has four filter wheels: the blue and red imaging filter wheels, and the blue and the red below-slit wheels. The last two are only used for grating spectroscopy and usually contain neutral-density filters only, used to attenuate the calibration lamps.

Each of the two imaging filter wheels has 9 positions of which 8 are available for mounting filters and one is kept free. Order-sorting 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 red-arm 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 vice-versa (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.

EMMI Filters (basic set). In order of type and wavelength


ESO	Filter	wavelength (nm)	width (FWHM)	Peak efficiency %	Cell type	Files

EMMI Red arm
Broad-band filters
605	Bb	413.9	109.8	68	R3	PS\|dat
606	V	542.6	104.4	87	R3	PS\|dat
608	R	641.0	154.2	80	R3	PS\|dat
610	I	798.5	155.2	94	R3	PS\|dat
611	Z	>843.4	lwp	88	R3	PS\|dat
772	Gunn g	509.4	75.1	87	R2	PS\|dat
773	Gunn r	676.4	80.9	85	R3	PS\|dat
774	Gunn i	806.0	142.3	94	R2	PS\|dat
775	Gunn z	997.3	52.2	97	R	PS\|dat
776	Tyson B	445.6	146.2	87	R	PS\|dat
Narrow-band filters
587	He I	448.0	4.8	53	R1	PS\|dat
652	He II	469.3	7.3	62	R1	PS\|dat
672	Spec.	472.2	28.6	79	R1	PS\|dat
771	H Beta cont.	477.5	7.4	81	R	PS\|dat
770	H Beta	486.2	7.8	77	R3	PS\|dat
765	Spec.	489.5	14.9	79	R2	PS\|dat
673	Spec.	502.8	2.66	77	R1	PS\|dat
766	Spec.	505.9	21.2	83	R2	PS\|dat
589	O III / 0	501.1	5.5	61	R2	PS\|dat
590	O III / 3000	505.6	6.2	50	R2	PS\|dat
591	O III / 6000	511.1	6.1	69	R2	PS\|dat
592	O III / 9000	515.6	6.4	67	R2	PS\|dat
593	O III / 12000	520.8	6.7	63	R3	PS\|dat
594	O III / 15000	525.7	6.8	66	R3	PS\|dat
767	Spec.	546.4	20.7	75	R2	PS\|dat
768	Spec.	602.6	53.8	92	R2	PS\|dat
654	H Alpha	656.0	3.3	36	R3	PS\|dat
596	H Alpha / 0	656.8	7.3	54	R3	PS\|dat
597	H Alpha / 3000	663.1	6.6	60	R3	PS\|dat
598	H Alpha / 6000	668.5	6.7	55	R3	PS\|dat
599	H Alpha / 9000	676.0	7.1	51	R3	PS\|dat
600	H Alpha / 12000	683.3	7.2	55	R3	PS\|dat
601	H Alpha / 15000	689.4	7.3	58	R3	PS\|dat
653	N II / 0	658.8	3.0	56	R2	PS\|dat
595	N II / 0	660.7	7.1	55	R3	PS\|dat
655	S II / 0	672.8	7.5	53	R3	PS\|dat
656	Spec.	912.9	19.3	89	R3	PS\|dat
657	S III / 0	954.0	10.5	89	R2	PS\|dat
795	Spec	435.9	93.1	80	R2	PS\|dat
796	Spec	539.8	95.7	89	R2	PS\|dat
Order-sorting filters
643	BG38 2mm	481.9	276.9	96	R2	PS\|dat
645	OG530 3mm	>530.0	lwp	95	R1	PS\|dat
646	RG715 3mm	>721.5	lwp	98	R3	PS\|dat
769	BG39	472.2	237.2	86	R3	PS\|dat

EMMI Blue arm
602	U Bessel	354.2	54.2	67	B	PS\|dat
603	B Bessel	422.3	94.1	66	B	PS\|dat
658	EUV (UG11/5)	<366.1	swp	70	B	PS\|dat
647	Ne V	342.2	8.3	39	B	PS\|dat
648	O II / 0	372.5	6.9	35	B	PS\|dat
649	O II / 5000	379.5	6.7	44	B	PS\|dat
650	O II / 10000	385.3	7.0	43	B	PS\|dat
651	O II / 15000	392.7	7.8	41	B	PS\|dat
671	He II	468.0	15.2	57	B	PS\|dat
588	He II	469.0	6.6	71	B	PS\|dat
723	Spec.	394.9	3.5	44	R	PS\|dat
644	GG375 3mm	>369.2	lwp	99	B	PS\|dat

Cell type:
B: Blue-arm filter, mounted perpendicular to the beam
R1: Red-arm filter, mounted with a tilt of 2.5 deg
R2: Red-arm filter, mounted with a tilt of 5.0 deg
R3: Red-arm filter, mounted with a tilt of 7.5 deg.