DECam filter information

DECam has a large collection of optical filters available (7 broad-band filters and and 9 narrow-band).

Broad-band Filters

The broadband filters are u, g, r, i, z, Y, and VR, which are very similar to their analogously named counterparts from other surveys. The filters used by the Dark Energy Survey (DES) are g, r, i, z, and Y. Uniquely, the DES z band has greater sensitivity at longer wavelengths than the SDSS z band and overlaps with the DES Y band.  The VR filter is primarily of interest to those searching for or studying objects in our solar system.

Narrow-band Filters

Over the years, a collection of narrow-band filters have been added to the collection of DECam filters, although we note that many of them have some restrictions for their use. Most of the narrow-band filters have been purchased by teams to carry out specific science projects, and the use of these privately-owned filters is governed by MOUs with AURA. The MOUs make the filters available to the NOIRLab and Chilean communities for use in their own programs, but do not permit duplication of the science for which the filter was purchased. Any community scientist wishing to use a DECam narrow-band filter should therefore initiate a correspondence with the relevant filter PI well before writing a proposal. Any resulting proposal should include a summary of the correspondence with the filter PI.

As an exception to this general requirement, the N501 and N673 filters may be freely used for proposals to study emission line objects at low redshift without prior approval. These two filters were originally designed by the ODIN survey to enable identification of Ly alpha emitters at high redshifts, but they encompass the wavelength of emission lines [OIII] and [SII], respectively, allowing their use for studying emission nebulae in our own or nearby galaxies.

Narrow-band filter N395, centered on the Ca II H and K lines, can be used freely by the community.

Note on filter availability

The DECam Filter Changer Mechanism provides positions for only eight filters. Because installing and removing filters from DECam is a non-trivial procedure that needs to be carried out with great care during daytime, we plan for filter changes only a few times each semester to accommodate the needs of the different approved programs. While the g, r, i, and z filters will always be available on DECam, the other filters will not be available at all times.

Filter response

• The DES standard bandpasses as used in the DES Data Release 1 (DR1) is available in the following table (available in both fits and ascii formats). This table, also known as version Y3A2_20170715,isan updated characterization of the Blanco/DECam total system response (instrument and atmosphere) for the g, r, i, z and Y bands. The system responses (grizY columns) includes the total throughput of the system (instrument + atmosphere). If you want the system throughput without the atmosphere, divide the grizY column by the atm column.For more info, see the DR1 paper. Notice that this new calibration does not imply changes of the filters/CCDs over time. Thus, this table is relevant for use with all DECam data since September 2012. The responses in this table have not been normalized. 
  • Fits table
  • Ascii table
  • README

DES DR1 Standard Bandpasses for the DECam g, r, i, z and Y filters.

The bandpasses represent the total system throughput, including atmospheric transmission (airmass = 1.2) and the average instrumental response across the science CCDs.

• The u filter is not part of the DES Standard Bandpass System. Total throughput for this filter comes from the DECam Science Verification phaseand it is available in this table (thanks to William Wester, DES Collaboration)

DECam filters ugrizY throughput (with no atmosphere)

• Filter transmission (area weighted response) from Asahi for u,g,r,i,z,Y and VR (plot)
• Properties of the VR filter
• Properties of the N964 filter
• Properties of the N662 filter
• Old ugrizY throughput measurements: this is provided for legacy use only (e.g. trying to reproduce earlier published results). The DR1 values provided above are to be used by default. Notice that the u-band measurements in this table are identical to the one provided above.
• See FAQ if you are planning to observe with no filter (don't!)