Rolling shutter

The "rolling shutter" concept is related to the shutter not reading out the exposure values at once, but rather scanning across the sensor vertically or horizontally. This implementation could be mechanical, as with the shutter curtain on the Micro Four Thirds cameras, or electronical, as when the sensor output is read during a video recording.

This is not strictly related only to digital cameras. Older film based cameras often feature a focal plane curtain shutter, which "rolls" across the film plane and exposes the film horizontally or vertically. A very famous example of this is the racing car picture taken in 1913 by Jacques Henri Lartigue using a 4x5 Speed Graphic camera.


The shutter moves relatively slowly on this camera, when compared with modern SLRs, which gives the distortion of the racing car. The distortion is especially visible in the wheels, which appear to be leaning forward. This effect was later copied by cartoonists when they wanted to give the impression of speed.

The term "rolling shutter" is not only used to describe the mechanical or electronic shutter implementation, but also the distortion itself. You're not likely to see this distortion effect when using Micro Four Thirds cameras, since the shutter is moving very fast. You must take a picture of something very fast moving to be able see the effect.

One such example is recording a rotating propeller. Here are two images captured from a 1080-line video recording using the Panasonic Lumix GH1 camera and the Panasonic Lumix 20mm f/1.7 pancake lens.



While the camera is exposing the video frame vertically, the propeller is moving, making it look bent. In reality, the propeller blades are straight, of course.

Rolling shutter distortion artifacts can be very annoying in video. You may see this as a "wobbling" when the photographer is panning horizontally. Luckily, the GH1 handles this rather good when recording videos. In normal use, you'll need to look very closely to find these artifacts in typical video captures.

I have made a study of the amount or rolling shutter distortion in Panasonic GH1 and GH2. It seems that the GH2 is slightly better than the GH1. Even though I generate rolling shutter artifacts in my study, they are not commonly seen in real life usage. So this is not any big issue at all.