The function of dark adaptation and light adaptation of the light or on the Retina in the eye

The retina of our eyes has two different types of sensory cells or receptors, on the one hand the cones (for day vision) and on the other hand the rods (for night vision).

All photoreceptors are stimulated by the amount and spectrum of radiation. The cones are active in bright surroundings and automatically switch off in the dark. Although they are not very sensitive, unlike the rods they can Recognise colours. There are three types of cones. Each of the three cones has a different sensitive frequency range. A distinction is therefore made between Sensors for blue, green-yellow and red.

Seeing at night with binoculars

For night vision are the sticks (approx. 120 million). These are very sensitive to weak light stimuli (but cannot perceive colours and only react to differences in brightness and movement. The retina's sensitivity to light and dark is considerably increased. If you go outside at night from an illuminated room, the cones gradually switch off and the rods become active.

Until the rods have reached their highest possible sensitivity, it takes up to 45 minutes - This adaptation period is also referred to as "Dark adaptation". Over the course of this period, sky observers recognise fainter and fainter stars. After just 15 minutes, the intensity of the dark adaptation has increased by a factor of 50,000. If you use white light at this point, you have to adapt again. After the start of the adaptation period, the Retinal pit no longer records images, it is switched off. In this state, the eye is colour-blind and sharp vision along the visual axis is no longer possible.

This is also the reason, why a misaligned telescope can no longer be focussed at night. This problem, which hunters have so far paid insufficient attention to, can be solved by focussing the binoculars on the expected main shooting distance while it is still bright and then adjusting the focus to this distance. SettingAlignment in binoculars refers to the parallel alignment of the two halves of the binoculars. " More info marked. The eye only sees sharply in a very small area. This area is a small circle on the retina with a diameter of approx. 2 mm, which corresponds to a ray entrance angle through the pupil of only 2°. It is precisely in this area that the visual fossa is located.

The Retinal pit is a depression in the retina, where the point of sharpest vision is located in bright light. The density of cones is highest in the retinal pitThere are no rods in it. The density of the cones decreases towards the edge of the retina. These then mix with the rods located further out on the retina.

For this reason, objects can be seen most clearly during the day when looking directly at them, whereas at night you have to look slightly past the object to see it clearly. For example, an object seen at TwilightFor night glasses, which are ideal for sitting game and as sow glasses, the light intensity is the most important feature. " More info The alternating sow is difficult or impossible to recognise with direct vision and only becomes visible with indirect vision (the gaze wanders back and forth).