the focal length of a lens measured in metres: a power of +5 dpt therefore has a reciprocal length of 1/5 metres or 20 centimetres. What is long-sightedness? In the case of long-sightedness, the eyeball is [...] There is no standard answer to this question, as it differs for each vision task: a visual acuity of 0.1 is sufficient for a person to be able to orientate themselves outdoors. However, a visual acuity of [...] of the field of view. With only two standard batteries, the necessary voltage is stepped up to the 3.6 volts required. The step-up converter used here guarantees bright, even illumination over a long period