The CFHTLS ugriz filter set

This page describes the CFHTLS ugriz filters and contrasts them with the SDSS ugriz filters.

Obviously, most the information presented in this page is available elsewhere. However, although it was possible to find the CFHTLS filter transmission function without the telescope (mirrors, optics, detector) response function, it is hard to find files describing the filter set with multiplication with the system response (which are necessary for a number of things, notably photometric redshifts), so they are presented here.

The filter responses were multiplied by the telescope (mirror+optics+CCD) response to obtain total transmissions for the whole system. These total transmissions are shown as the heavy coloured lines The final response curves are given in text format here:

• u band
• g band
• r band
• i band
• z band

The transformation between the Vega and AB magnitude system is different for the SDSS and MegaCam filters, particularly for the U. This is shown in the following table:

These numbers are computed for zero airmass.

The colour terms between the two filter sets can be described by the following equations:

u_Mega = u_SDSS - 0.241 (u_SDSS - g_SDSS)
g_Mega = g_SDSS - 0.153 (g_SDSS - r_SDSS)
r_Mega = r_SDSS - 0.024 (g_SDSS - r_SDSS)
i_Mega = i_SDSS - 0.085 (r_SDSS - i_SDSS)
z_Mega = z_SDSS + 0.074 (i_SDSS - z_SDSS)

The relations for the griz bands come from the analysis of the SNLS group. The relation for the u band comes from the CFHT web pages.