R. Mirzoyan et al., ON THE OPTICAL DESIGN OF VHE GAMMA-RAY IMAGING CHERENKOV TELESCOPES, Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment, 373(1), 1996, pp. 153-158
Optical characteristics of some operational and future VHE atmospheric
imaging gamma ray telescopes are discussed. It is shown that due to l
arge longitudinal size of a TeV air shower in the atmosphere, which is
comparable to its average distance to a measuring telescope there is
a type of optical aberration, that is proportional to diameter of the
used reflector (depth of field). The use of imaging telescopes with es
sentially larger than 10 m diameter reflectors leads to deterioration
of image quality which can strongly affect the accuracy of measured im
age parameters and the gamma-hadron separation power. It is shown that
the edges of a reflector of spherical design in the case of large rel
ative aperture A (A greater than or equal to 1) have to be bent toward
s the reflectors axis in order to provide the smallest spot size.