Abstract This paper reports the observability of distant gamma-sources using groundbased imaging air-Cherenkov telescopes with low energy thresholds like the MAGIC telescope. In particular we focus on extragalactic sources at low and high redshift which are emitting gamma photons up to very high energies. AGN for example are one of the most promising candidates for multiwavelength observations. The presented calculation is easy to apply on any extragalctic source emitting gamma-rays in the GeV/TeV energy range e.g. gamma-ray bursts (GRB). The data taken with a gamma-telescope (groundbased or airborne), have to be corrected for extragalactic absorption due to the metagalactic radiation field (MRF). The multiwavelength compain of the MAGIC telescope is breavely discribed.

Keywords AGN: Blazars Spectra - Metagalactic Radiation Fields: UV-IR - Imaging Cherenkov Telescopes: MAGIC

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