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When longer wavelengths of visible and near-infrared radiation pass into the eye, they are absorbed by the dark pigment epithelium below the retina. The energy is converted into heat that can literally cook the exposed tissue. Photocoagulation destroys the rods and cones, leaving a permanently blind area in the retina. This thermal damage also occurs during extended exposure to blue and green light.

 

Both photochemical and thermal retinal injuries occur without the victim's knowledge, as there are no pain receptors in the retina, and the visual effects do not occur for at least several hours after the damage is done.

When longer wavelengths of visible and near-infrared radiation pass into the eye, they are absorbed by the dark pigment epithelium below the retina. The energy is converted into heat that can literally cook the exposed tissue. Photocoagulation destroys the rods and cones, leaving a permanently blind area in the retina. This thermal damage also occurs during extended exposure to blue and green light.

Both photochemical and thermal retinal injuries occur without the victim's knowledge, as there are no pain receptors in the retina, and the visual effects do not occur for at least several hours after the damage is done.

Lensrentals.com has posted a blog entry in which what happened to some of their rental equipment that were used without proper solar filtering during a recent total eclipse in the United States is shown in photos of the damaged equipment.

Lensrentals.com has posted a blog entry in which what happened to some of their rental equipment that were used without proper solar filtering during the recent Great American Eclipse in the United States is shown in photos of the damaged equipment.

• Height of the sun above the horizon. The closer the sun is to the horizon, the more atmosphere it has passed through before you see it. The atmosphere reflects, absorbs, and dissipates this energy so that less of it reaches a viewing location on the ground.

• The optical density of the atmosphere. Clear dry air allows much more of the sun's energy to reach the surface than air thick with water vapor and other particulates in it. On heavily overcast days the position of the sun can not be seen at all from the surface. Most days at most places are somewhere in between these two extremes.

• Lens focal length/magnifying power/maximum aperture. The size of a lens' entrance pupil (effective aperture) determines how much of the sun's energy is collected by the lens. The larger the entrance pupil, the more energy is collected when all of the other variables are constant. An 18-55mm f/3.5-5.6 lens has a maximum entrance pupil diameter of less than 10mm. A 600mm f/4 lens has an entrance pupil diameter of 150mm and collects 225X as much of the sun's energy as the 55mm f/5.6 lens does!

• The length of time the lens collects the sun's energy. The longer a lens is pointed at the sun the more energy it collects. Heat that is collected faster than it can be dissipated raises the internal temperature of the camera. If the components get too hot, they can be damaged.

• The same is true for the human retina, which is generally less tolerant of direct exposure to the sun's energy than most modern cameras. With that 600mm f/4 lens mentioned above, your eye can be almost instantly damaged enough to blind it by looking directly at the sun without an adequate solar filter! Heat that is pumped into an eye faster than the body can dissipate it can "cook" the rods and cones in the retina, leading to permanently impaired visual function or even total blindness. Since the retina has no pain receptors, you won't even feel it as the infrared energy from the sun heats your retinal tissue. The effect of the damage from that heat can take up to several hours, so by the time you realize you have a problem it is far too late to do anything about it.

• Height of the sun above the horizon. The closer the sun is to the horizon, the more atmosphere it has passed through before you see it. The atmosphere reflects, absorbs, and dissipates this energy so that less of it reaches a viewing location on the ground.

• The optical density of the atmosphere. Clear dry air allows much more of the sun's energy to reach the surface than air thick with water vapor and other particulates in it. On heavily overcast days the position of the sun can not be seen at all from the surface. Most days at most places are somewhere in between these two extremes.

• Lens focal length/magnifying power/maximum aperture. The size of a lens' entrance pupil (effective aperture) determines how much of the sun's energy is collected by the lens. The larger the entrance pupil, the more energy is collected when all of the other variables are constant. An 18-55mm f/3.5-5.6 lens has a maximum entrance pupil diameter of less than 10mm.¹ A 600mm f/4 lens has an entrance pupil diameter of 150mm and collects 225X as much of the sun's energy as the 55mm f/5.6 lens does!

• The length of time the lens collects the sun's energy. The longer a lens is pointed at the sun the more energy it collects. Heat that is collected faster than it can be dissipated raises the internal temperature of the camera. If the components get too hot, they can be damaged.

• The same is true for the human retina, which is generally less tolerant of direct exposure to the sun's energy than most modern cameras. With that 600mm f/4 lens mentioned above, your eye can be almost instantly damaged enough to blind it by looking directly at the sun without an adequate solar filter! Heat that is pumped into an eye faster than the body can dissipate it can "cook" the rods and cones in the retina, leading to permanently impaired visual function or even total blindness. Since the retina has no pain receptors, you won't even feel it as the infrared energy from the sun heats your retinal tissue. The effect of the damage from that heat can take up to several hours, so by the time you realize you have a problem it is far too late to do anything about it.

_{¹ Keep in mind that the pupils in your eyes are usually around 2-4mm in diameter in bright light. Even that 55mm f/5.6 lens is letting about nine times as much of the sun's energy into the camera. With an SLR, a portion of that energy is allowed through the semi-reflective part of the mirror that allows light to go to the autofocus sensor array. Some of it is absorbed by the viewscreen at the top of the light box that is viewed through the viewfinder. But most of that energy is concentrated into the viewfinder's small exit pupil.}