Broadband filters - the Harris set

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

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

B:1mm BG12 + 2mm BG39 + 1mm GG385
V: 2mm BG39 + 2mm GG495
R: 2mm OG570 + 2mm KG3

An I band filter of the same thickness has been added to all of the Harris sets, this is refereed to as a ``Harris I'', although it was not defined as such by Harris. The recipe is:

I: 4mm RG9

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.

Note that the transmission in B is significantly (about 30%) lower than in Kitt Peak B.