Welcome to the HiPERCAM/ULTRACAM/ULTRASPEC filter database.

HiPERCAM/ULTRACAM can use five/three different filters at a time, each mounted in a cartridge which must be manually loaded into the instrument. The filters for ULTRACAM 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. 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.) The filters for HiPERCAM are kept in the wooden box. There are 10 cartridges in total, 5 of them in the instrument and 5 of them in the wooden box. The cartridges include foam pads which can accommodate filters of different thicknesses, so do not use shims with the HiPERCAM filters. ULTRASPEC is only a single-beam instrument and hence uses a 6-position filter wheel. There is a spare wheel located alongside the wooden box containing the filters, sitting inside the humidity-controlled cabinet in the dome. When changing ULTRASPEC filters in the wheel, you need to use the black plastic shims to prevent the filters from moving within their slots.

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 below for info), i.e. there is no change in focus when introducing a different filter in the f/2.3-2.5 beams of the HiPERCAM/ULTRACAM/ULTRASPEC cameras. Asahi achieve this by designing each filter to be slightly thicker/thinner to allow for their differing refractive indices. This means that nearly all of the filters are interchangeable between the HiPERCAM, ULTRACAM and ULTRASPEC instruments. If you are interested in procuring a new filter for one of these instruments, or you wish to change the location of the filters (e.g. to use some of the ULTRACAM filters, currently in Chile, with HiPERCAM, currently on La Palma), 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. For HiPERCAM, which has 5 channels covering all of the SDSS filters, there is no need to even consider using the clear filters.

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), mapt = Manuel Torres (IAC). 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/2.3-2.5 beams of the HiPERCAM/ULTRACAM/ULTRASPEC cameras. This causes a slight shift in the bandpass, which has been reflected in the central wavelength (λ_cen) values quoted below, except for the SDSS and Halpha very narrow 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.

For ULTRASPEC on the 2.4m TNO, we procured a new SDSS filter set in May 2012. These are virtually identical to the original ULTRACAM set, and should be parfocal with them. We have also borrowed the second set of narrow-band 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').

For HiPERCAM, we procured a new SDSS filter set in September 2015. These filters should also be parfocal with the other ULTRACAM and ULTRASPEC filters. The data below are given for the as-built filters and are for a parallel beam. The central wavelength and FWHM values are quoted from Fukugita et al. (1996). I have called these filters set No. 3 to avoid confusion with the ULTRACAM (No.1) and ULTRASPEC (No.2) SDSS filter sets. We also procured a set of "Super" SDSS filters in May 2017. Set No.1 will be used with ULTRACAM. Set No.2 will be used with HiPERCAM. Unfortunately, when numbering these two sets of filters, I mixed up the Asahi No.1 and No.2 sets, so the HiPERCAM No.2 set listed in the filter table below is actually composed of the Asahi u No.2, g No.1, r No.1, i No.2, z No.1, and vice-versa for the ULTRACAM No.1 set. This doesn't really matter though, as the data files are identical for both sets of filters. 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.