Glare refers to the visual conditions that cause visual discomfort and reduce the visibility of objects due to inappropriate brightness distribution or extreme brightness contrast in space or time in the field of vision. Glare can be divided into direct glare, reflected glare and contrast glare. So, how does glare come into being and what are the hazards?
1、 What is glare
All lenses will be affected by some non ideal factors in the process of their image transmission. One of these aberrations is called glare.
Camera lens is composed of many individual glass lenses, which are called lens units. When bright light passes through the camera lens, part of the light will be reflected back by the various surfaces of these lens units. This internal reflection can cause a phantom and appear on the final photo like an image. For example, a small seven sided spot near the top right of the picture is glare.
2、 How Glare Is Generated
Glare is mainly caused by the angle between the position of the light source and the viewpoint. The extremely bright light source, the highly high light or strong brightness contrast generated by reflection, will cause glare to the audience. The glare in the exhibition environment includes one emitting glare and the glare generated by secondary reflection. Glare will not only cause visual discomfort, but also damage vision and even cause blindness. For the display light environment, it is important to control the glare.
3、 Hazards of glare
1. Discomfortable type
Discomfortable glare refers to discomfort felt in some too bright environments, such as sitting in a strong sun to read a book or watching a high brightness TV in a dark house. When the vision of the human eye must be switched in an environment with a large difference in brightness, it will feel uncomfortable. This uncomfortable situation will cause a kind of escape action of the eyes and reduce vision.
Conclusion: The results of glare mainly fall into three types: discomfort glare, light adaptive glare and disability glare. Therefore, when you encounter a pipeline that you are not used to, you can close your eyes and take a rest to avoid the damage to your eyes caused by glare.
2. Light adaptive type
Another kind of glare is called light adaptive glare, which refers to the phenomenon that when people walk from dark cinemas (or underground tunnels) into the sun, their binocular vision decreases. The main reason is that a strong glare source forms a central dark spot on the retina of the human eye, causing a long time of blurred vision. When some people suffer from fundus diseases (especially macular disease), the response to this glare will be more severe because the light sensing cells on the retina have impaired their light adaptation function.
3. Disability type
The last type of glare is called disabling glare. Dying glare refers to the phenomenon that the contrast of human retinal image decreases due to the surrounding messy glare sources, which makes it difficult for the brain to analyze the image. It is similar to the performance that the projection of the slide projector on the wall is interfered by the nearby strong light, which leads to the decline of the image quality.
There are many eye factors that can cause disabling glare. The most common one is elderly cataract patients. When the human eye lens starts to appear dot opacity, the light entering the eye will be scattered, which makes the patient feel blurred (because dot opacity is often composed of tiny particles, the light scattered is mainly short wavelength light, such as blue light).
In addition, with the increase of age, the ability of the human eye lens to absorb and process ultraviolet rays will also decline, and some stray light caused by this will also produce disabling glare that affects the quality of retinal imaging (the lens will stimulate stray light with wavelength close to 530nm after absorbing 310-410nm ultraviolet rays); The light is composed of visible light and invisible light, and the invisible light includes ultraviolet light and infrared light, so it is necessary to distinguish the types of glare light sources and the causes of glare to prevent glare in clinical practice.
4、 Solutions to Glare
1. Use the hood
If the light is right on the edge of the image, installing a hood on the lens will eliminate the glare (but if the light is right in front, the hood can do nothing).
2. Adjust the aiming direction of the lens
Look for shooting directions that can eliminate glare. Sometimes, as long as it deviates slightly from the direction of the light source, the glare on some points may be eliminated. However, what should we do if the photographed subject does not allow the camera to move or rotate?
3. Block the light source
Block the light source direction with your hand (or hat, cardboard) at a certain position in front of the lens. Make sure the occluders are high enough, or they will appear in the viewfinder.
Conclusion: Glare will affect vision, so the solution is to use a hood or block the light source.