The night vision devices are different from the telescopes. Between the objective lens and eyepiece there is an image amplifier, therefore focus needs to be adjusted at both sides (both at the objective lenses and at the eyepieces). Somewhat similar to camcorders where the image is produced on a small screen and then an eyepiece is used to magnify the image. The performance of a night vision devide depends on the objective lens size, focal ratio and the properties of the image amplifier. In Hungary beside the first generation devices the 2nd and 3rd generation devices are also allowed to use.