We present a new approach to the composite spectra construction based on stacking spectra with similar slopes α λ within the wavelength range redward of Lyα emission line, which allows to reduce the typical noise. With the help of this technique a detailed study of the HI Lyα-forest region (λ rest ≈ 1050 − 1200 Å) of the own sample of 3439 medium-resolution quasar spectra from SDSS DR7 was performed. More than 14 lines were found within this wavelength range, three of which were known from

more »

... ous studies of quasar composite spectra from SDSS and some others were known in composite spectra from space-based telescopes or high-resolution spectra of individual quasars from ground-based telescopes.