Filters

Color filters are provided in the spectrograph optical path, after the image slicer. Their main function is to suppress wavelengths outside the observing band, to optimize stray light performance. There is a tilt of 4 degrees between the plane of the filter and the optical axis in order to avoid ghosting due to reflections from the filter surfaces. However, as discussed in the section on scattered light, it is not expected that most programs will require the use of filters. There is space for ten filters within the filter wheel, but only four filters are currently installed. Two filters, the BG40 and the CuSO₄, are used for the removal of red light when observing in the blue. Two additional filters, GG495 and OG530, can be used for the removal of blue light when observing in the red. Transmission profiles as a function of wavelength for each of the four filters are shown below.

GG 495 Filter Click image for larger version.	OG 530 Filter Click image for larger version.
BG 40 Filter Click image for larger version.	CuSO4 Filter Click image for larger version.

Last update September 1, 2005; Steven Margheim