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(*) k = 3/2, rm = 58 mm, a = 28.7°, ft = 0at4,000A. Over-correction s = 1.042 with flattener lens. Grating optical figure: ZOpt = 6.021 10—5 r2 — 5.42 10—9 r4 — 9.8 10—14 r6 — 2 10—18 r8. Aspherized grating LOOM/Jobin-Yvon, 1,200£.mm—1, 1st-order, 116x132mm. Camera-collimator angle = 28.7°.

Fig. 4.16 UVPF spectrograph of CFHT - Residual aberrations on the thinned CCD when centered at 4,000 A. The two other positions, obtained by sliding the field lens with CCD each side on a cylinder, show a similar amount of residual aberrations without refocussing in all the spectral range 3,000-5,200 A

Fig. 4.16 UVPF spectrograph of CFHT - Residual aberrations on the thinned CCD when centered at 4,000 A. The two other positions, obtained by sliding the field lens with CCD each side on a cylinder, show a similar amount of residual aberrations without refocussing in all the spectral range 3,000-5,200 A

with the Marly spectrographs (Lemaitre and Kohler [36]) of Haute Provence and Nanjing observatories, and Carelec spectrograph (Lemaitre et al. [37]) of the 2 m f/5-f/15 telescope in Haute Provence. The optical designs of these instruments have shown that axisymmetric gratings can provide excellent image quality with positions deviating substantially from normal diffraction ft = 0 up to ft = 12

Fig. 4.17 Schematic view of catoptric spectrographs MARLY f/8-f/3.2 and CARELEC f/15-f/2.5, using axisymmetric aspherized gratings of 66 and 100 mm central groove length respectively. The mounting angle between the collimator and camera axes is = a + ft = 30° [37]

or 15°. The addition of a holed folding mirror (Fig. 4.17) in the camera optics provides better access to the detector and its cryostat. Several vase-form active sub-masters allowed aspherizing by air pressure plane standard gratings from Jobin-Yvon with the optimal profile geometry k = 3/2. CARELEC is equipped with five axisymmetric aspherized gratings designed for various pair angles a, ¡30 (Table 4.4).

Table 4.4 Axisymmetric gratings of CARELEC Spectrograph f/2.5xf/2.15
0 0

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