The guide telescope is extremely necessary when doing astrophotography, the UltraGuide MKII is a telescope with a focal length of 120mm for a ratio of F / 4.0, ideal for instruments with medium or short focal length. The 31.8mm focuser allows you to use the UltraGuide MKII both as a finder and as a guide telescope, in fact it is equipped with a T2 thread to allow attachment to most of the guide cameras on the market.