filters




Welcome to the ULTRACAM filter database. ULTRACAM can use three different filters at a time, each mounted in a cartridge which must be manually loaded into the instrument. The filters are kept in the blue case, along with spare cartridges. There are 8 cartridges in total, 3 of them in the instrument, and 5 of them in the blue case, as indicated by the cartridge? column in the table below. The blue case also contains plastic shims, which must be used to hold thinner filters securely in the cartridges. (Be careful not to overshim, however, as it is then possible to crack the filters.) Nearly all of the filters have been procured from Asahi Spectra Co., Japan. They are of dimension 50mmx50mmx~5mm and nearly all of them have an identical optical thicknesses (see the construction column for info), i.e. there is no change in focus when introducing a different filter in the f/2.3 beam of the ULTRACAM cameras. Asahi achieve this by designing each filter to be slightly thicker/thinner to allow for their differing refractive indices. If you are interested in procuring a new filter for ULTRACAM, please contact Vik Dhillon.

Please bear in mind that the cut points of the dichroics define which combinations of three filters can be used with ULTRACAM. Filters which mount in the blue arm of ULTRACAM are highlighted in blue in the name column below, filters which mount in the green arm are coloured green, filters which mount in the red arm are in red, and filters which can mount in any arm, i.e. the clear filters listed below, are in white. The latter are far from ideal, however, for two reasons: 1. They do not reject light longward of the dichroic cut points in the blue and green arms, resulting in contaminated photometry. 2. For this reason, and also because in the red arm the entire r'-z' range is accepted, the image quality is much poorer than when a narrower-band filter is used. More precisely, the blue and green arms have not been designed to bring red light to a good focus, and the slight change in image scale and aberrations with wavelength in the red arm means r'-z' images are not as sharp as those taken in the individual r', i', z' filters. If the highest throughput photometry is absolutely essential, it is recommended that only the red arm is used with a clear filter, as this brings the largest gains in terms of increased efficiency and suffers from the least image-quality problems.

In the table below, vsd = Vik Dhillon, trm = Tom Marsh (Warwick), tsh = Tariq shahbaz (IAC), jcv = Jorge Casares (IAC), spl = Stuart Littlefair (Sheffield), mm = Mihalis Mathioudakis (QUB), ar = Andrea Richichi (NARIT). In each plot, the filter transmission is shown by the black curve, and is measured data from the delivered filter, not a theoretical model (unless otherwise stated). Note, however, that this data is measured in a parallel beam whereas the filters are used in the f/2.3 beam of ULTRACAM's cameras. This causes a slight shift in the bandpass, which has been reflected in the central wavelength (λcen) values quoted below, except for the SDSS filter values, which are quoted for a parallel beam. To prevent confusion with the filter names, I have tried to use the same names that were used by Asahi when procuring the filters. The No.1 and No.2 at the end of some of the filter names indicates that two of each of these filters were procured.

If you change a filter in ULTRACAM, remember to enter the details on Tom's filter changes web form at: http://www2.warwick.ac.uk/fac/sci/physics/research/astro/people/marsh/ultracamfilters. A record of all filter changes can be found at: http://deneb.astro.warwick.ac.uk/phsaap/ultracam_filter_changes.html.

UPDATE on 2012/05/21: We have procured a new SDSS filter set for ULTRASPEC on the 2.4m TNO. These are virtually identical to the original ULTRACAM set, and should be parfocal with them. We have also borrowed the second set of filters ordered by Jorge and Mihalis for use with ULTRASPEC (apart from the two NBF filters, which are still with Mihalis). We also moved one of the clear and NaI filters from ULTRACAM to ULTRASPEC, as indicated in the location column. We also procured an SDSS i'+z' filter and a KG5 filter (effectively SDSS u'+g'+r').

UPDATE on 2017/05/09: The Super SDSS filters have arrived! Set No.1 will be used with ULTRACAM. Set No.2 will be used with HiPERCAM. These filters should be parfocal with the other ULTRACAM and ULTRASPEC filters. Note that the data given below are for the as-built filters. Note also that the curves, central wavelength and FWHM values are for a parallel beam and are for the filter bandpass alone, i.e. they do not include the effects of atmosphere, telescope/instrument optics, CCD QE (which are included in the SDSS central wavelength and FWHM values). The Super SDSS z' filter has been arbitrarily cut off at 10000Å when calculating the central wavelength and FWHM.


Last updated: vsd @NTT 23-May-2017

# name λcen
(Å)
FWHM
(Å)
throughput construction location procured cart-
ridge?
notes
1 SDSS u' 3557 599 plot, data info ULTRACAM vsd; Aug 01 y
2 SDSS g' 4825 1379 plot, data info ULTRACAM vsd; Aug 01 y see u' data for format info
3 SDSS r' 6261 1382 plot, data info ULTRACAM vsd; Aug 01 y see u' data for format info
4 SDSS i' 7672 1535 plot, data info ULTRACAM vsd; Aug 01 n see u' data for format info
5 SDSS z' 9097 1370 plot, data info ULTRACAM vsd; Aug 01 n see u' data for format info
6 Clear No.1 - - plot, data info ULTRACAM vsd, tsh; Mar 03 n only consider for red arm
7 Clear No.2 - - plot, data info ULTRASPEC vsd, tsh; Mar 03 n
8 Clear No.3 - - plot, data info ULTRACAM vsd, tsh; Mar 03 n only consider for red arm
9 CIII/NIII_HeII No.1 4662 108 plot, data info ULTRACAM vsd, jcv; Apr 04 n
10 Red continuum No.1 6010 118 plot, data info ULTRACAM vsd, jcv; Apr 04 n
11 NaI No.1 5912 312 plot, data info1, info2 ULTRACAM vsd, spl, tsh; Mar 05 n FWHM from spec
12 NaI No.2 5911 312 plot, data info1, info2 ULTRASPEC vsd, spl, tsh; Mar 05 n FWHM from spec
13 Halpha broad No.2 6554 94 plot, data info1, info2 ULTRACAM vsd, jcv; Dec 06 n
14 Blue continuum No.2 5149 158 plot, data info1, info2 ULTRACAM vsd, jcv; Dec 06 n
15 NBF 3500Å No.1 3499 102 plot, data info1, info2 ULTRACAM vsd, mm; Sep 07 n No.2 with mm
16 Halpha narrow No.1 6564 54 plot, data info1, info2 ULTRACAM vsd, mm; Oct 07 n
17 NBF 4170Å No.1 4169 52 plot, data info1, info2 ULTRACAM vsd, mm; Oct 07 n No.2 with mm
18 SDSS u' No.2 3557 599 plot, data info ULTRASPEC vsd, trm; Nov 11 n cenwave & FWHM assumed same as No.1
19 SDSS g' No.2 4825 1379 plot, data info ULTRASPEC vsd, trm; Nov 11 n cenwave & FWHM assumed same as No.1
20 SDSS r' No.2 6261 1382 plot, data info ULTRASPEC vsd, trm; Nov 11 n cenwave & FWHM assumed same as No.1
21 SDSS i' No.2 7672 1535 plot, data info ULTRASPEC vsd, trm; Nov 11 n cenwave & FWHM assumed same as No.1
22 SDSS z' No.2 9097 1370 plot, data info ULTRASPEC vsd, trm; Nov 11 n cenwave & FWHM assumed same as No.1
23 CIII/NIII_HeII No.2 4662 108 plot, data info ULTRASPEC vsd, jcv; Apr 04 n Cracked - replaced with No. 31
24 Red continuum No.2 6010 118 plot, data info ULTRASPEC vsd, jcv; Apr 04 n
25 Halpha broad No.1 6554 94 plot, data info1, info2 ULTRASPEC vsd, jcv; Dec 06 n
26 Blue continuum No.1 5149 158 plot, data info1, info2 ULTRASPEC vsd, jcv; Dec 06 n
27 Halpha narrow No.2 6564 54 plot, data info1, info2 ULTRASPEC vsd, mm; Oct 07 n
28 SDSS i'+z' No.1 8385 2905 plot, data info ULTRACAM vsd, ar; Jun 12 n cenwave & FWHM calculated from #21 & #22
29 SDSS i'+z' No.2 8385 2905 plot, data info ULTRASPEC vsd, ar; Jun 12 n cenwave & FWHM calculated from #21 & #22
30 KG5 5075 3605 plot, data info1, info2 ULTRASPEC vsd, trm; Oct 13 n Schott 668nm short-pass filter, no AR coating
31 CIII/NIII_HeII No.3 4657 112 plot, data info ULTRASPEC vsd; Jun 14 n Replacement for No. 23
32 N86 8611 122 plot, data info ULTRASPEC ar; Nov 14 n For lunar occultations
33 Super SDSS us No.1 3526 827 plot, data info1, info2, info3 ULTRACAM vsd; May 17 y cenwave & FWHM for filter alone
34 Super SDSS gs No.1 4732 1493 plot, data info1, info2, info3 ULTRACAM vsd; May 17 y cenwave & FWHM for filter alone
35 Super SDSS rs No.1 6199 1374 plot, data info1, info2, info3 ULTRACAM vsd; May 17 y cenwave & FWHM for filter alone
36 Super SDSS is No.1 7711 1467 plot, data info1, info2, info3 ULTRACAM vsd; May 17 y cenwave & FWHM for filter alone
37 Super SDSS zs No.1 9156 1694 plot, data info1, info2, info3 ULTRACAM vsd; May 17 y cenwave & FWHM for 10000Å cutoff