4.3 The optical design of the spectrometer

The photo, principal design and optical scheme of the mid-resolution spectrometer for observation of a wide field of the twilight segment and mesosphere silver clouds (NLC) are presented. The problems of allocation of MSO spectra in «pure» form are discussed.

The optical design of the spectrometer its design and appearance

Therefore, during the preparation of expedition to the North Kazakhstan Region in 2006, for noctilucent cloud observations, we have designed and made up a celestial spectrometer with the angular field of 20o along all the spectral slit length. This is of a moderate-resolution spectrometer with a transparent diffraction grating of 250 touches per 1 mm and a registration of the spectrum in the first order on a large-formatted (36×24 mm) CCD camera of STL11000M. To eliminate an influence of the second order spectrum at λ> 700 nm, we used “Red Glass-14” (a glass filter). At input of the spectrometer, we put a standard objective of Jupiter-3 with an aperture ratio of (1:1.5) as the supplying optics. It formed an image of the investigated part of the sky of 20o high on the entrance spectral adjustable slit. A cine-projection objective of 16KP-1.2/50 served as a collimator. As a camera lens, we used a standard photo objective of Jupiter-9.

For a confident identification of the NLC spectral details registered, we used an additional digital camera. We placed it on the same platform on which there was the spectrometer. Their optical axes’ directions were coincided. Sighting at a part of NLC being studied we carried out through the NLC sighting tube. The spectrometer platform could rotate independently in vertical and azimuthal directions. Depending on the observation problem, a rotation angle could reach 90o to orient the spectrometer slit in both vertical and horizontal position. This turned out to be essentially important when there was the possibility of obtaining spectra of individual NLC parts and twilight segment at the same zenith distance.

In Fig. 3.7 the exterior of the spectrograph is shown, and in Fig. 3.8 — its optical scheme.

Fig. 3.7 The exterior of the celestial spectrometer.

Fig. 3.8 Optical scheme of the spectrograph


  1. Supplying lens Jupiter-3 (1:1.5)
  2. Adjustable entrance slit of the spectrograph
  3. Collimating lens 16KP-1.2/50
  4. Filter RG-14 cropping the second order
  5. A transparent diffraction grating of 250 touch/mm
  6. Camera lens Jupiter-9
  7. Large formatted CCD-camera STL-11000M



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