Spectrograph Design

Optical design of our spectrograph is that of Musicos by Baudrand & Bohm (1992, A&A 259, 711). Dr Baudrand kindly provided us with know-how and blueprints. Both comfort of construction and optical quality of this inexpensive spectrograph were already proven by several groups who cloned Musicos. Our choice of the optical parts and materials follows closely that of Musicos. However, we decided to have no moving parts in the spectrograph and were further restricted with what was available locally for our low budget project. Hence different mechanical design and construction of our spectrograph, by Roman Baranowski. Optically our design implements the red channel of Musicos and is consistent with our interest mostly in red stars.

Dr Baudrand’s design is of modern, effective echelle type and makes no compromise on the quality of the essential element, the high grade Richardson echelle grating (Fig. 1). At the same time huge saving was achieved by employing a high shelf commercial photographic lens for the camera. The lens were carefully chosen and thoroughly tested by design’s author for its smooth spectral transmission. The optical parts before assembly are illustrated in Fig. 2.

Fig. 1. The optical design of Musicos (from Baudrand and Bohm, 1992; A&A 259, 711). In our instrument there is only one prism (SF5) for the red domain. Another difference is in the type of CCD chip.

Fig. 2. Optical parts of the Poznań spectrograph and some test gear, before assembly.

Fig. 3. The spectrograph in its box in the old telescope dome in Borowiec.