The Diopter Telescope or Dioptometer is a focusing telescope measuring the power of lenses in diopters. The results of the measurement can be read off on a graduated scale. The measurements with Diopter Telescopes include following steps:
• the eyepiece of the Diopter Telescope is rotated until its reticle is seen sharp and clear. The focusing ring is set to zero.
• the Diopter Telescope is placed with its supporting flange on the eyepiece or the telescope under test. The eyepiece of the telescope under test is rotated until its reticle is seen sharp and clear. This is the zero setting of the eyepiece.
• Further measurements are made by rotating the eye-piece under test to the next graduation and focusing the Dioptometer correspondingly. The reading is done directly on the diopter graduated scale.