Safety Precautions - Canon EF 300mm f/4L IS USM Instruction

a Safety Precautions
(1) Whether it is attached to the camera or not, do not leave the lens under the sun without the
lens cap attached.
This is to prevent the lens from concentrating the sun's rays which can cause a fire.
(2) Do not look at the sun or a bright light source through the lens or camera.
Doing so can result in loss of vision. Looking at the sun through the detached lens is especially
hazardous.
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