Broadband filters - the Harris set (BVR)

To replace a deteriorating set of Kitt Peak filters, 3 sets of large (125 mm) BVR glass colour filters were purchased in 1990 for CCD imaging.

The filters consist of cemented stacks of Schott glass, following the recipe below (see also NOAO newsletter 11,12 and 14:

B: 2mm BG12 + 2mm BG39 V: 2mm OG570 + 2mm KG3 R: 1mm BG12 + 2mm BG39 + 1mm GG385

It is thought that

• When the filter response curves are convolved with a typical CCD response, the glass filters provide a closer match to the standard Johnson B and V and the Kron-Cousins R bandpass.
• The transmission of the glass filters is comparable to that of the interference filters, and does not deteriorate with time.
• Glass filters are significantly cheaper than interference filters of the same size.

Harris filters are very often used at La Palma, just like Kitt Peak filters, probably because both are on the Kron-Cousins system. Note that the transmission in B is significantly (about 13%) lower than in Kitt Peak B. See Figs  16 and  17 for details of these filters.