[COMMUNITY PROJECT] Deriving comprehensive guidelines for shooting the sun without sensor damage
The focal length of the lens is a crucial factor and times will not be largely independent of focal length! Briefly, the temperature reached by a pixel heated by light will depend on the rate of heating and the rate of loss of heat. The rate of heating will vary as the light intensity. The rate of loss of heat is primarily by conduction of the heat to the surrounding pixels and the rest of the sensor, and will depend on the temperature difference between the pixel and the surroundings (Newton's law of cooling). Suppose you double the focal length of the lens at the same f-number, then the rate of heating of the pixel is the same as the light intensity is the same, but it will be spread over 4x the area. Accordingly, the rate of loss of heat at the centre of the image will be lower as there will be a larger number of heated pixels surrounding the centre and they will be of similar temperature to the central pixels and so there will be lower lateral conduction conduction of heat away. Accordingly, the pixels in the image will heat up faster and reach a higher temperature as the focal length increases at constant f-number. (And this is why telephoto lenses can even damage shutters, both the total amount of light hitting the shutter and the rate of loss by conduction are crucial).Meaning that the following durations should be safe for exposure to the full-intensity sun:
(largely independent of focal length)
f/1.2 f/1.8 f/2.8 f/4 f/5.6 f/8 f/11 ≤1 s ≤2 s ≤5 s ≤10 s ≤20 s ≤40 s ≤75 s
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