Simple testing of concave telescope mirrors is discussed. Method uses a point light source in the infinity and a small lens in front of the focus of the mirror under test. Lens consists of two spherical surfaces and can be easily manufactured. Distance of the lens from the focus of the mirror under test is about a few centimeters, therefore the lens can be fastened to an interferometer for testing optics, to Foucualt or Ronchi tester, etc. It is necessary to use a flat mirror or collimator in an optical shop; in the space it is possible to use a light of stars. It is intended to use that method for controlling of the concave hyperbolic mirror of the Space Ritchey-Chretien telescope 1.7 m in diameter and f/2.74.