The GMOS filters u', g', r', i' and z' are similar to the filters used by the Sloan Digital Sky Survey (SDSS). A description of the SDSS photometric system is presented in Fukugita et al. (1996, AJ, 111, 1748). See the description of optical photometric standard stars for details on the photometric standard calibration.

Please note that due to filter degradation discovered in semester 2004A the u' filter is no longer available for science use on GMOS-N. We are considering replacing this filter.  It is also possible to install User-supplied filters in GMOS.

The filter CaT is a 150nm broad-band filter approximately centered on the Ca Triplet.

The Z and Y filters are similar to those installed in the United Kingdom Infra-Red Telescope (UKIRT) Wide Field Camera (WFCAM). A description of these filters is available from the UKIRT WFCAM user guide, see Table 1.1. The Z filter is designed to mimic the SDSS z' bandpass with red sensitive CCDs, while the Y filter occupies the clean wavelength range between the atmospheric absorption bands at 0.95µm and 1.14µm. 

The filters Ha, HaC, OIII, OIIIC, SII, HeII, and HeIIC are narrow-band filters for H-alpha, H-alpha continuum, ionized oxygen, ionized oxygen continuum, ionized sulphur, ionized helium, and ionized helium continuum, respectively.

The filter DS920 is a narrow-band filter centered on a wavelength region of very low sky background. This filter is only available with GMOS-N, and may be removed to make room for a u' filter.

The filters GG455, OG515, RG610 and RG780 are 5mm thick Schott glass filters. These are long-pass filters which can be used to block 2nd-order contamination of the spectra or limit the wavelength range to allow multiple slit-banks in the multi-aperture mode. The RG780 filter is only available with GMOS-S.

Transmission curves for each filter set based on lab measurements are available: GMOS-N filters and GMOS-S filters (The new Z and Y filters will be added once they have been characterized).

The table lists the properties of the filters based on laboratory measurements. The wavelength interval given in the tables is the interval within which the transmission is larger than 50 per cent. For the long-pass filters and the z' filters the wavelength at the 50 per cent transmission at short wavelength edge is given.

Some of the filters can be combined, the allowed combinations are listed last in the table. The combinations are useful for using the IFU in 2 slit mode with the higher dispersion gratings, e.g. R831 with the filter combination r' + RG610.

Imaging with GMOS requires use of either a color filter (griz, CaT, Z, Y) or a narrow band filter. The long-pass filters GG455, OG515, RG610, and RG780 are not suitable for imaging. Also imaging without a filter is not supported since neither GMOS is equipped with an Atmospheric Dispersion Corrector (ADC) at this time.

Users may supply their own filters for queue observations; see filter policy and specifications for details.

*The filter name is the concatenation of filter and filter number e.g. HeII_G0340 for the GMOS South HeII narrow-band filter.