Infrared reflection (the first cause)
Most cameras illuminate at night with infrared (IR). If there is a nearby wall, a ceiling, glass, or even dust in the air in front of it, that light returns to the lens and produces white haze. The remedy: move the camera away from nearby surfaces, and never shoot through glass — a window reflects the IR straight back onto the lens.
A dirty lens or a spider web
Dust, a fingerprint or a strand of web on the lens shows no effect by day, but at night it scatters the IR light and fogs the whole image. And spiders are drawn to the warmth and light of the camera, so they spin in front of it. Clean the lens gently with a soft cloth — that alone resolves many cases.
Condensation and humidity
In the humid climate of the Eastern Province, vapour can condense inside the camera housing or on the lens at dawn, fogging the image. A camera with a sealed housing (a suitable protection rating) and a correct installation reduces this; repeated condensation is a sign of a poor housing or a seal that was not made properly.
Backlight and glare
A strong floodlight or a lamp in the field of view creates glare that blinds part of the image and turns faces into black silhouettes. Adjust the camera away from direct light sources, or use a camera with wide dynamic range (WDR) to balance the exposure.
The type of night vision itself
If you want a clear colour image at night, an ordinary IR camera gives you black and white only. Colour night-vision cameras (such as ColorVu) need some ambient light to work in colour. Sometimes the “blur” is not a fault but the limits of the camera type against what you expect from it.
