WFI Filter Characteristics

This web page supersedes any information concerning the filters in any other manual or document.

Description

This page describes the characteristics of the ESO WFI filters that are permanently mounted in the filter wheel.

Notes on other Filters / Special Filters

Due to the special characteristics of the WFI filters, we do not normally mount special filters or even other filters from the ESO collection in the filter wheel. If you would like to use special filters, you must first get agreement from SciOp, and then provide the filters to La Silla at least 2 months prior to the observations.

WFI Filter Characteristics

The transmission data and characteristics given in the below table for the WFI filters were measured by the opticians at La Silla. Note that the filters are either circular (with a diameter of 210mm), or square (6"x6"==152x152mm). The square filters will cause very slight vignetting (for further details, please refer to Figure 4 in the WFI User Manual).

Note that the transmission changes over the filter due to the different incident angle of the beam over the filter. This effect will cause the central wavelength to shift bluewards by about 0.001 at the centre of the filter, and by 0.002 at the edge of the filter. For example, if you had a filter with a true central wavelength of 500nm, then in the WFI the central wavelength of the filter in the centre of the filter would be 499.5nm, while at the edges of the filter the central wavelength would be 499.0nm.

Note that the Rc filter causes some vignetting in the corners.

Naming convention: all filters which are permanently available at the WFI are assigned ESO IDs. If the filter does not have a special name (U, B, V etc) then the assigned name is "CWL/FWHM" where CWL is the truncated central wavelength (in nm) and FWHM is the truncated full-width at half-maximum (in nm). If the filter has a special name, the FWHM of the filter (in nm) is appended to the special name.

Zeropoints and colour terms of UBVRI filters on WFI can be found here.

Abbreviation Meaning
CWL Central WaveLength
FocOff Focus offset (in eu) relative to the B/99 filter: focus(X) = focus(B/99) + offset(X)
FWHM Full-Width at Half-Maximum
Leak Does filter have a redleak? (most leaks beyond CCD QE cut-off)
LWP Long Wave pass (i.e. red cut off defined by CCD)
Pos The Position of the filter in the WFI `filter wheel'.
PT The percentage transmisison at the PWL.
PWL Peak WaveLength (i.e. Wavelength with highest transmittance).
SC In Service: part of standard calibration
Type Either C (circular filters, diameter of 210mm) or S (6"x6" square filters).
Filter CWL FWHM PWL PT Type Leak FocOff Transmission Data Notes
Name ESO# Pos (nm) (nm) (nm) (%)     (eu) Table Graph General Quality (*) SC
---Broad Band Filters (FWHM > 35nm)---
U/50 877 12 340.4 73.2 350.3 82.35 S y -100 (TEXT) (GIF,PS) Broadhurst filter U350/6, old name: U/360 use with care yes
U/38 841 6 363.690 38.264 362.5 51.6 S n -75 (TEXT) (GIF/PS) ... acceptable no
U ... *n ... ... ... ... ... ... -735 ... ... Small Loiano U;
U Capodimonte		 bad no
B/99 842 11 456.252 99.014 475.0 91.2 S y 0 (TEXT) (GIF/PS) ... acceptable no
BB#B/123_ESO878 878 14 451.100 133.500 502.500 88.5 S y -80 (TEXT) (GIF/PS) new B filter ... yes
V/89 843 13 539.562 89.386 523.0 87.0 S n -100 (TEXT) (GIF/PS) ... acceptable yes
Rc/162 844 15 651.725 162.184 668.5 93.9 C y -50 (TEXT) (GIF/PS) ... good yes
Ic/lwp 845 17 783.845 LWP 1001.0 97.6 C n -55 (TEXT) (GIF/PS) See note 1 good no
BB#I/203_ESO879 879 16 826.9 203 760.0 86.957 S ... -127 (TEXT) (GIF/PS) EIS filter ... yes
Z+/61 846 18 964.819 61.598 956.1 95.1 S y -20 (TEXT) (GIF/PS) Formerly Z+/60 (see note 3) acceptable no
---Medium Band Filters (FWHM > 15nm)---
416/29 872 38 416.651 29.859 421.0 75.5 S n -5 (TEXT) (GIF/PS) ... acceptable (6) no
445/18 873 32 445.520 18.175 451.5 82.8 S n -40 (TEXT) (GIF/PS) ... good no
461/13 874 24 461.478 13.750 464.5 83.3 S n -11 (TEXT) (GIF/PS) ... acceptable (6) no
485/31 860 7 485.809 31.458 485.0 88.7 S n -40 (TEXT) (GIF/PS) ... use with care no
516/16 871 49 516.497 16.204 519.5 89.6 S n -50 (TEXT) (GIF/PS) ... use with care no
518/16 862 8 518.829 16.345 519.5 88.7 S n -35 (TEXT) (GIF/PS) ... use with care no
531/17 875 9 531.504 17.652 531.0 86.8 S n 0 (TEXT) (GIF/PS) ... use with care no
Washington M ... 36 ... ... ... ... ... ... ... ... ... No ESO number(?) ... no
513/15 ... 37 ... ... ... ... ... ... ... ... ... No ESO number(?) acceptable no
549/16 ... 10 545.8 11.652 546.0 77.1 ... ... ... (TEXT) (GIF/PS) No ESO number(?), use with care no
Gieren 501 ... 35 ... ... ... ... ... ... ... ... ... Gieren_501_2/2.7 good no
571/25 863 27 571.348 25.515 571.5 88.7 S n -45 (TEXT) (GIF/PS) ... use with care no
604/21 864 33 604.301 21.049 605.0 93.7 S n -30 (TEXT) (GIF/PS) ... acceptable no
620/17 866 39 620.887 19.423 624.5 95.1 S n -5 (TEXT) (GIF/PS) ... use with care no
646/27 867 30 646.287 27.665 637.5 90.7 S n -10 (TEXT) (GIF/PS) ... acceptable no
679/19 868 41 679.300 19.703 681.0 90.9 S n -30 (TEXT) (GIF/PS) ... use with care no
696/20 869 26 696.288 20.689 695.5 93.1 S n -20 (TEXT) (GIF/PS) ... use with care no
721/25 847 40 721.794 25.646 721.5 89.5 S n -40 (TEXT) (GIF/PS) ... use with care no
753/18 848 29 753.229 18.292 751.5 94.4 S y -25 (TEXT) (GIF/PS) ... acceptable no
770/19 849 22 770.464 19.433 771.0 95.6 S y -25 (TEXT) (GIF/PS) ... acceptable no
790/25 850 42 790.610 25.941 791.0 68.3 S y -20 ... ... See note 5 use with care no
815/20 851 23 815.871 20.928 821.4 82.7 S n -20 (TEXT) (GIF/PS) Formerly 815/27 (see note 3), acceptable no
837/20 852 43 837.765 20.071 842.7 87.1 S y -10 (TEXT) (GIF/PS) Formerly 838/25 (see note 3) good no
856/14 853 21 856.212 14.329 857.1 88.3 S y -20 (TEXT) (GIF/PS) Formerly 855/20 (see note 3) good no
884/39 870 44 884.164 39.731 890.1 95.1 S n -55 (TEXT) (GIF/PS) MB#914/27-ESO854
listed in OS
See note 3		 good no
914/27 854 20 914.799 27.496 918.3 93.3 S y -25 (TEXT) (GIF/PS) Formerly 915/28 (see note 3) use with care no
---Narrow Band Filters (FWHM < 15nm)---
396/12 865 31 396.329 12.864 399.0 66.1 S n -50 (TEXT) (GIF/PS) ... acceptable no
OIII/8 859 4 502.393 8.034 502.0 88.4 S y -15 (TEXT) (GIF/PS) ... acceptable no
OIII/2 N/A 28 502.612 2.818 502.6 80.1 S n -30 (TEXT) (GIF/PS) See note 2 good no
504/10 861 34 504.678 10.291 504.0 88.8 S n -40 (TEXT) (GIF/PS) ... acceptable no
Halpha/7 856 19 658.827 7.431 658.5 90.7 S y -10 (TEXT) (GIF/PS) ... acceptable no
665/12 858 25 665.561 12.078 667.5 86.4 S y -25 (TEXT) (GIF/PS) ... acceptable no
SIIr/8 857 3 676.340 8.42 675.8 84.3 S n -30 (TEXT) (GIF/PS) See note 4 acceptable no
NB 810/6 ... 2 ... ... ... ... S n -100 (N/A) (N/A/N/A) MPIA/
Meisenheimer		 bad no
NB 824/7 ... 5 ... ... ... ... S n -100 (N/A) (N/A/N/A) MPIA/
Jones et al		 use with care no
NB 817/7 ... 45 ... ... ... ... S n -100 (N/A) (N/A/N/A) MPIA/
Meisenheimer		 use with care no
---Miscellaneous---
White ... 1 ... ... ... ... C ... -30 ... ... ... ... no
BtLght-WFI(1) ... 50 ... ... ... ... ... ... ... ... ... ... ... no
Black Paper ... 46 ... ... ... ... ... ... ... ... ... ... ... no
Misc Empty Holder ... 47 ... ... ... ... ... ... ... ... ... ... ... no
PinHolePlate ... 48 ... ... ... ... ... ... ... ... ... ... ... no

Notes from table:

(1) CWL is the short wavelength edge.
(2) Property of Observatory of Capodimonte. Availability and quality not guaranteed. Note that this filter is 144x144mm.
(3) Due to an error in the set-up of the filter transmission measurement machine, an error was made in the measurement of the filter's central wavelength and FWHM. These filters were remeasured, and this database was updated to reflect these changes (and subsequently new names) on December 16 1999. The former filter name is indicated in the table (note, 884/39 did not undergo a name change).
(4) Prior to 8 Feb.2000, this filter was mistakenly identified as SIIr/5.
(5) Prior to 8 Mar. 200, this filter had an incorrect Tx curve plotted.
(6) Tracker chip reflection strongly affects flatfielding.
(*) In the last column (Notes), "Quality" refers to the measured image distortion introduced by the filter and the appearance of ghost images. Bad quality means large image distortion and/or astigmatism and/or ghost images, medium quality means some elongation in the images.
(*n) Currently not mounted in filter wheel.