This page describes a simple experiment to illustrate a main different between CMOS and CCD image sensors.

-CMOS Image Sensors
Light is absorbed by the image sensor column after column as the shutter is being opened.

-CCD Image Sensors
Light is absorbed by the entire array of the image sensor at the same time, after the shutter is opened.

Description of Experiment:

1. Find a long piece of cable or rope.

2. Tie one end of the cable to a horizontal beam on the roof.

3. Let it hang from the roof and do not let it touch the ground. Tie the excess rope or cable in a bundle together. Or you can also tie a piece of rock to the end of the rope.

4. Hold the rope to the side until it is at about 45 degrees to the vertical and let it swing.

5. Make sure the cable is straight when it is swinging. Otherwise, you need to add more weight to the end of the cable.

6. Take pictures of the swinging cable using your digital camera.

This experiment is carried out using the Ennyah Tech DigiCam ES3310 digital camera, which has a CMOS image sensor, and the Kyocera SL400R, which has a CCD image sensor.

Picture of Swinging Cable taken using DigiCam ES3310 (CMOS sensor)
(Click on image or link to view full size image)

swing_es3310.jpg

Picture of Swinging Cable taken using Kyocera SL400R (CCD sensor)
(Click on image or link to view full size image)

swing_SL400R.jpg

My Observations:

-Straight Swinging Cable Becomes Curved in CMOS Camera
As can be seen in the pictures above, the straight swinging cable becomes curved in the picture taken by the CMOS camera DigiCam ES3310. In a similar picture taken by the CCD camera Kyocera SL400R, the cable looks straight.

This is because the CMOS image sensor absorbs light column after column as the shutter is being opened. Thus, there is a delay between the time when the top row is activated and the time when the bottom row is activated. This causes the swinging cable to look curved in the picture.

In contrast, the CCD image sensor takes the whole picture in one go. Therefore, it is able to capture a single shot of the straight swinging cable.

Therefore, next time when you take pictures of fast moving objects using CMOS cameras, it is wise to take note of this often neglected property.