Appendix 6 - Filters.

  1. Filters Available
  2. Filter Holders and Wheels
  3. Filter Bandpasses                  


Introduction The Telescope & Optics The Detectors
The Imaging Cameras An Imaging Cookbook The Data you Take Away
Exposure times OFFSET_RUN files CCD Windows Data Catalogs
On-line Reduction Filters Flat-fields Blank Fields Orientation Shutters

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The AAO's imaging filter `inventory' is currently somwhat confused. It is hoped this page will eventually list all the AAO filters available for imaging, their usual locations, how they were made, and what their throughput is (both in table and plot form).

Until that happens, however, if this page does not contain the information you are looking for, you should contact AAO staff for help. Steve Lee (sl@aaocbn.aao.gov.au) will almost always be able to answer your question - but requests should be directed through Chris Tinney (cgt@aaoepp.aao.gov.au), who is the AAO astronomer responsible for imaging.

Filters Available

The filters all come in one of two types - they are either interference filters, or broadband filters made with Schott glasses. For broadband applications, the interference filters generally have better throughput and a `squarer' profile than the Schott glass filters. Of course, the standard photometric passbands are generally not very square, making the interference filters a poorer match to them. In general, however, 4m telescope imaging projects are more interested in going deep, than high precision photometry, in which case the intereference filters are obviously to be preferred. In practise they are used almost exclusively.

A range of `narrow-band' interference filters are available. Some of these (in particular the Taurus and Taurus Tuneable Filter, or TTF) are very good, having peak transmissions of over 90%. Some are quite poor, with peak tranmissions of only 50%, so be careful which filter you choose.

The tables below list the available sets of filters, and includes the `recipes' for the filters (where available) and the appropriate focus offsets for use with the DOUBLET CORRECTOR.  Section 3.1.6 discusses the difference between triplet and doublet focus.  The Filter Bandpasses section contains hyperlinks to tables of bandpass information, and GIF files containing graphs pf the band passes.

Of all the filters listed below, only the KPNO set and the f/1 set see much action.


Filter Thickness
(mm)
Focus Offset
(mm)
Details Comments
1 U 10 3.35 1mm UG1+
5mm CuSO4(liquid)
Liquid CuSO4
has bubbles
2 B 5.7 2.05 KPNO Interference set
3 V 5.6 2.10 KPNO Interference set
4 R 3.1 1.10 KPNO Interference set
5 I 3.2 1.30 KPNO Interference set

Filter Thickness
(mm)
Focus Offset
(mm)
Details Comments
6 B 6 2.0 2mm GG385 + 1mm BG12 +
1mm BG18 + 2mm KG3
Low trans. Rarely used.
Marked #1
7 V 6 2.05 2mm GG495 + 2mm BG18 +
2mm KG3
"
Marked #2
8 R 6 2.12 2mm RG610 + 2mm KG3 +
2mm BG20
"
Marked #3
9 I 3 1.05 3mm RG9 "
Marked #4
10 BJ 6 2.02 2mm GG385 + 2mm BG28 +
2mm KG3
Match phot. J emulsion.
Marked #5
11 RF 8 2.95 2mm RG630 + 3mm BG20 +
1mm BG38 + 2mm KG3
Match phot. F emulsion.
Marked #6B,RF
12 IN 5 1.88 3mm RG695 + 2mm KG2 Match phot. N emulsion.
Marked #7
13 B* 6 2.11 2mm GG385 + 2mm BG18 +
2mm KG3
Broad B
Marked #8
14 R* 4 1.32 2mm RG610 + 2mm KG3 Broad R
15 RG695 3 1.0 3mm RG695 Marked #10
16 RG780 3 1.0 3mm RG780 Marked #11
17 RG830 3 1.0 3mm RG830 Marked #12
18 KG3 2 0.8 2mm KG3 Marked #13
19 O* 4 1.3 2mm OG570 + 2mm KG3 Very broad R filter.
Marked O*

 

Central
Wavelength
(nm)
Bandwidth
(nm)
Peak
Transmission
660 11 45%
669 12 48%
681 12 56%
690 8 44%
709 8 46%
712 13 40%

Filter Thickness
(mm)
Focus Offset
(mm)
Details Comments
  B 5 1.88 2mm GG395 + 1mm BG12
+ 2mm BG40
Focus estimated from
thickness (not measured)
  R 4 1.32 2mm OG570 + 2mm KG3 "
  I 2 0.8 2mm RG9 "

Filter Thickness
(mm)
Focus Offset
(mm)
Details Comments
  B       Focus estimated from
thickness (not measured)
  V       "
  R       "
I       "
V+R       "

 

 

Filter Thickness
(mm)
Focus Offset
(mm)
Details Comments
  B 4 1.32 2mm GG385 + 1mm BG12 +
1mm BG39
Focus estimated from
thickness (not measured)
  V 4 1.32 2mm GG495 + 2mm BG39 "
  R 4 1.32 2mm OG570 + 2mm KG3 "
I 4 1.32 4mm RG9 "
U 4    1mm UG1 + 3mmBG40 "

Filter Thickness
(mm)
Focus Offset
(mm)
Details Comments
  B 7 2.39 4mm GG395 + 1mm BG12 +
2mm BG39
Focus estimated from
thickness (not measured)
  V 5 1.88 2mm GG495 + 3mm BG39 "
  R 5 1.88 2mm OG570 + 3mm KG3 "
I 3 1.05 3mm RG9

Filter Thickness
(mm)
Focus Offset
(mm)
Details Comments
  B 5 1.88 Focus estimated from
thickness (not measured)
  V 5 1.88 "
  R 5 1.88 "
I 5 1.88 "
U 5 1.88 "

 

 

 

 

 

Filter Optical
Thickness
(mm)
Focus Offset
(mm)
Central
Wavelength
(nm)
Bandpass
(nm)
Diam.
(")
Comments
469.5 2.6 3
501.7 4.5 3
587 3 3
630 4 3
658.3 4.5 3
673.4 4.5 3
872 1 3
TTF Blocking Filters are summarised by this figure.
I0 665.0 21 4.85 These are designed to sit in gaps in the atmospheric OH emission bands.
I1 710.0 28.5 4.85
I3 760.0 32.6 4.85
I5 815.0 37.2 4.85
I6 855.0 38 4.85
I8 910.0 46.4 4.85

Filter Optical
Thickness
(mm)
Focus Offset
(mm)
Central
Wavelength
(nm)
Bandpass
(nm)
Size
(")
Comments
  H alpha 1.45 0.78 656 19 10x10
[O II] 1.80 1.14 373 6 5x5
H gamma 1.80 1.14 434 6 5x5
He II 1.77 1.11 468 7 5x5
H beta 1.71 1.05 486 7 5x5
[O III] 1.79 1.13 501 8 5x5
He I 1.74 1.08 587 9 5x5
[O I] 1.75 1.09 630 9 5x5
H alpha 1.65 0.99 656 10 5x5
[S II] 1.60 0.94 672 10 5x5
cont (1.53) (0.86) 365 10 5x5
cont 1.85 1.20 460 20 5x5
cont 1.70 1.04 540 40 5x5
cont 1.69 1.03 643 10 5x5


Filter Holders and Wheels

f/3.3

All filters mount in a slide which is inserted into the camera head a few centimetres under the CCD Adaptor Plate. Filters (eg. the photographic interference filters, the 160mm ANU filters, or the 100mm LDSS filters) can be inserted into these slides singly. Alternatively, there are three wheels which can be installed in a modified filter slide and inserted into the Camera Head.

Three such wheels are available:

  1. A six position wheel - holds up to six filters,  either 50mm square or 2.25 inch diameter, and up to 11mm thick. This is the standard wheel used with the standard set of UBVRI broad-band filters.
  2. A three position wheel - holds up to three filters, up to 75mm in diameter, and up to 11mm thick.
  3. A three position wheel - holds up to three filters, up to 83mm in diameter, and up to 11mm thick.

f/1

The f/1 camera has its own motorised filter 'jukebox' into which 3 filters can be mounted before your run starts. It is a non-trivial excercise to change these during the night, so this should be avoided.


  

 

 

Filter Bandpasses

The following table contains hyperlinks to all the AAO filters for which band-pass information is currently available. The Files pointed to contain one line of header information, and the rest of the file is two ASCII numeric columns - the first is wavelength in nanometres, the second is throughput of the filter in % at that wavelength. The Figures pointed to are each about 7K in size. The Peak Throughputs are provided to give a rough comparison of the efficiency of different filters. The Approximate Bandwidths are FWHM - for asymmetric filters, like the glass R filters, it is only a crude estimator of the actual width, while for long pass filters like the glass I, it is meaningless.  To obtain the `actual' throughput you will get on the telescope for any of the broad filters, the QE curve of the detector must also be factored in.

 

Set Filter Fig
?
File Peak
Throughput
(%)
Approx.
Bandwidth
(nm)
KPNO 50mm sq. U(CuSO4) aao_cus04.txt 79% 65
B kpno_b.txt 85% 115
V kpno_v.txt 77% 120
R kpno_r.txt 92% 135
I kpno_i.txt 85% 175
50mm sq. glass B aao_glass_b.txt 56% 105
V aao_glass_v.txt 70% 90
R aao_glass_r.txt 73% 115
I aao_glass_i.txt 95% -
BJ aao_glass_bj.txt 58% 105
RF aao_glass_rf.txt 38% 55
IN aao_glass_in.txt 72% 160
B* aao_glass_bs.txt 73% 190
R* aao_glass_rs.txt 75% 125
RG695
RG780
RG830
KG3
O* aao_glass_os.txt 85% 160
LDSS 100mm Ø B
R
I
Gunn g 50mm g
f/1 Set 50mm Ø B
V
R
I
V+R
ANU 75mm Ø B anu_75_b.txt 59% 95nm
V anu_75_v.txt 78% 90nm
R anu_75_r.txt 73% 120nm
I anu_75_i.txt 88% -
ANU 160mm Ø U
B
V
R
I
H alpha Set 660nm
669nm
681nm
690nm
709nm
712nm
Photographic
Interference Filters
Halpha
10x10
[O II]
H gamma
He II
He beta
[O III]
He I
[O I]
H alpha
5x5
[S II]
cont 365nm
cont 460nm
cont 540nm
cont 643nm
Taurus 3" Ø 469.5nm taurus.469.2.dat 77% 2.6
501.7nm taurus.502.3.dat 95% 4.5
587nm 3
630nm 4
658.3nm taurus.658.4.dat 93% 4.5
673.4nm taurus.673.4.dat 97% 4.5
872nm 1
TTF 4.85" Ø Filters are summarised by this figure.
TTF 4.85" Ø I0 - 665nm 21
I1 - 710nm ttf.707.26.dat 87% 28.5
I3 - 760nm ttf.758.28.dat 89% 32.6
I5 - 815nm ttf.814.33.dat 76% 37.2
I6 - 855 38
I8 - 910nm ttf.909.40.dat 89% 46.4



Introduction The Telescope & Optics The Detectors
The Imaging Cameras An Imaging Cookbook The Data you Take Away
Exposure times OFFSET_RUN files CCD Windows Data Catalogs
On-line Reduction Filters Flat-fields Blank Fields Orientation Shutters

Back Contents Next

Last Contents Next

This Page maintained by : Chris Tinney (cgt@aaoepp.aao.gov.au)
This Page last updated:  28 Feb 1996, by Chris Tinney