I took a few pictures of cars on the highway at night with a 4-second shutter speed (automatic aperture and focus). Sorry for the blur in the second one, I left my tripod at home.
In the first picture, the initial positions of the cars are engulfed in headlight luminescence. In the second picture, however, a car was directly in front of the lens when the shutter opened. How/why does it completely disappear?
Technically, the car doesn't completely disappear. The few photons that were reflected from the dark car during the time it was in the frame were caught and recorded by the camera. It's just that there were a lot more photons reflected by the things that were stationary for the entire exposure time. There were also a LOT more photons captured that were emitted by the much brighter taillights. Those much greater quantities of photons from other things overpower the very few photons reflected by the car as it moved through the frame.
The car is dark, and it remained only for a short part of the 4s exposure at any one place. The background, on the other hand, is static and had therefor 4 seconds time to expose your sensor.
The lights, of course, are much brighter and needed much less time to register on your sensor.
In Night because of darkness, it seems like car is disappeared But in real it's not. Due to high speed it doesn't seems clearly.
