Sun mirror
A sun mirror , also known as a signal mirror , is a simple form of a heliograph that is used to draw attention to yourself over long distances using emergency signals . The mirror reflects the sunlight in the direction of the rescue workers. Sun mirrors are usually 5 × 8 centimeters in size (credit card size) or larger and made robust. In contrast to the heliograph, the sun mirror does not have a lock, but is held hands-free. The reflected light beam cannot be continuously held on the target by involuntary minute movements of the hand. Therefore, it is not suitable for emitting specific signals, but only generates a random flicker. The sun mirror is used in snow sports to send alpine emergency signals and in ocean shipping .
application
Since the sunlight spot reflected on the target can no longer be made out from a few hundred meters, a direction finding device is necessary in order to reliably flash even distant target points. Various designs have become established. What they all have in common is a (more or less) central peephole in the mirror.
- With the dipstick method , the target is sighted through the peephole with a dipstick. If the peephole, dipstick tip and target match and if the dipstick is immersed in the sunlight reflected by the mirror, the flashing beam also sweeps across the target. The thumb of the outstretched free hand can also be used as a dipstick. This technique must be performed with both hands.
- In the case of mirrors mirrored on both sides, the shadow of the mirror and in it the light point of the peephole (e.g. on the user's face) can be identified in the mirror image. For sighting, the mirror image of the point of light is brought into line with the peephole by turning and swiveling. As a result, the reflection beam and the direction of view through the peephole match.
- A third embodiment uses a reflective grating mounted in the peephole . This is coated with crystals that are retroreflective, i. H. Reflect light rays back to their light source. The non-mirrored back of the mirror in the peephole also reflects a little sunlight, in the same direction as the rest of the mirrored area. This light falls on the reflective grating and is reflected by the crystals in the opposite direction. If the reflected sunlight beam is aligned in such a way that it is in an extension of the line of sight (i.e. from the eye to the target), the sunbeams thrown back by the grid hit the eye and appear in the peephole as a light spot that is superimposed on the targeted target. This indicates to the user that the light beam reflected from the mirror surface is incident on the target.
If it is correctly aligned, the light signal is visible for many kilometers, and in clear weather it is theoretically only limited by the curvature of the earth .
An English rescue flash, on the other hand, is a stroboscope as a small hand lamp, which is often carried on life jackets or in lifeboats, and which is intended to mark the position of a person on the water for rescue workers in distress.
See also
Web links
- Rescue Flash - description, instructions, pictures