... The choice of the spectrograph design (Fig.2) is determined by the quantity R, the overall dimensions of the PF cage and the restrictions on the rigidity of the structure of the device. ... As the camera's objective a fast 4-lens aplanat is used having a focal distance F cam =140 mm and a relative aperture of 1:1.8, the resolution at the centre is no less than 80 gr/mm, that over the field at a distance of 3 mm from the edge along the frame ( ) diagonal is 35 gr/mm. ...