DIAGNOSIS Dirt, pollen, and spider webs on the lens are the main cause of blurry or hazy video, especially at night when the IR reflects off the grime. You just need to clean it without pushing debris into the seals.
FIX Use a dry, soft microfiber cloth—the kind you'd use for glasses or a camera lens. Gently wipe the main camera lens and the smaller, rounded motion sensor window in a circular motion. For stubborn spots, you can slightly dampen a corner of the cloth with distilled water only, wipe gently, and then immediately dry it with the dry part of the cloth.
IF THAT DIDN'T WORK If there's a film or hard water spots, a dedicated lens cleaning solution applied sparingly to the cloth (never sprayed directly on the camera) can work. Isopropyl alcohol (70% or less) on the cloth can also cut through grime, but use it sparingly.
HEADS UP Never use window cleaner, compressed air (can force moisture inside), paper towels, or abrasive cloths. They can scratch the lens coating or damage the water-repellent layer. Also, make sure the camera is powered off (remove the battery) before cleaning to avoid triggering motion alerts from your shadow.