Refractor telescope aperture 102 mm focal length 600 mm focal ratio 159 optical systems fraunhofer achromatic refractor suitable for enthusiasts beginners max useful magnification 204 x tracking equatorial mount equatorial mount exos 1 equatorial mount 4 eq4 tripod steel tripod telescope feature astrophotography suitable astrophotography function digiscoping lens barrel length 615 mm minimum useful magnification 14 series bresser messier reso