Sensors and rolling shutter

In my last post, I posted a video which involved a lot of fast movement and panning. Naturally, motion blur is going to occur with a sequence like this. However, a problem common to DSLR cameras is rolling shutter.

Rolling shutter is when, as with a camera sensor like the CMOS used in my Canon 550D, a frame isn't recorded at an exact moment - that is, part of the frame is captured slightly before another part. This leads to objects becoming warped when applying camera movement such as panning, or when an object passes the camera very quickly.

This leads to vertical objects appearing to 'lean' to one side on the recorded image.

Google images gives a good example of this in a photograph of a train:

This article explains why this occurs with most common consumer cameras. As the article states, CMOS sensors used in DSLR cameras typically use a rolling shutter rather than a global shutter, meaning that it "actually exposes different portions of the frame at different points in time, “rolling” through the frame" - although, this is due to the sensor "telling different portions to become light-sensitive at different moments in time",  rather than a physically-rolling shutter system.

CMOS sensors using a rolling shutter system are said to be more energy-efficient, which probably explains their usage in consumer products. This makes sense, but also makes it difficult to 'pull-off' quick motion on a small budget without it becoming distorted like the picture above.