Abstract. Here we want to report on significantly increased observation limits of imaging air Cherenkov telescopes. Typically these telescopes observe sources until the zenith angle 60°. There exist some observational results when sources were observed till the zenith angle 70°, but these suffer from systematic errors. One of the main problems with large zenith angle observation is related to the transparency of the atmosphere. At larger zenith angle observations the atmosphere is becoming significantly “thicker”. Thus, compared to small zenith angles, light that passes through the “thicker” atmosphere is stronger attenuated due to the scattering and absorption processes. Because of absence of reliable calibration of the atmospheric transmission, the Cherenkov light spectrum from air showers, measured at large zenith angles observations, suffers from uncertainties. This situation is becoming progressively more severe with increase of the observation zenith angle. We plan to report on observations of sources performed with the MAGIC imaging air Cherenkov telescope, extended till the zenith angle of 80°. This is a significant improvement compared to earlier observations. It provides longer measuring time for a given source and due to more than one order of magnitude increased collection area for air showers, improved statistics at the highest energies. The latter is a key issue for studying the highest energy gamma-ray emission from sources, especially from the so-called galactic PeVatron candidates. Such observations of MAGIC are supported by two methods for calibrating the transmission of the atmospheric. We plan to report on both methods.