The focus of the objective lens is very important for thermal imaging device since it influences such optical parameters as magnification and field of view. Thermal detection also depends on the focus of objective lens of thermal optic device. Different applications and goals require different parameters of the objective lenses. Thermal scopes come with three objective lenses differing in focal distance 19mm, 38mm, 50mm which is reflected in their names. In the Pulsar model range thermal imaging cameras with 30Hz and 50 HZ are marked with head letters H and X, e.g. Quantum HD or Quantum XQ respectively. Nowadays thermal imaging gained many fans due to its numerous advantages over classic night vision devices. The first and the main difference that underlies all benefits of thermal vision scope is its basic principle of operation. The detector can perceive even the slightest differences in temperature of various objects. The signal from detector is processed in electronic modules of thermal imaging camera and transferred to the screen. Temperature difference between the object and the background can often count up to a few dozen degrees and because of that on the screen the object is greatly distinguished from the background.