How a Camera Phone Works- Part 1

Cameras have come a long way from the original Pinhole Camera invented in the 12th century by Ibn Al-Haitham .  One of the fastest growing and most popular cameras is the camera phone. By 2009, the cumulative number of camera phones shipped since the inception of the camera phone category in this millennium will exceed the total number of all film and digital cameras shipped in the entire history of photography since the 1800s [Via Lyra.com]  So, I figured what a better place to start a blog about Digital Imaging then to talk about how a camera phone works.

I am going to break the camera phone into three major parts:

1. Lens Assembly
2. CMOS Image Sensor
3. Image Processing

Lens Assembly

The typical camera phone utilizes a fixed focus lens design.  The lens assembly consists of several components, this can be seen in the figure on the left.  The first part is the 3 element lens, which consists of 1 glass and 2 plastic elements.  This is then followed by an IR filter, the IR filter blocks any light above 780nm.  By removing the light above 780nm the sensor is able to only focus what the eye is able to see.  The figure below is an assembled camera phone assembly from Largan.  The typical optical properties of a camera phone lens are

• Effective Focal Length (EFL)  is 4.45
• F/Number  is 2.8

Since your typical cell phone camera is a fixed focus this lens have been optimized to be in focus from 100mm to infinity.  Of course this is not always the case and still has draw backs and in later blog entries we will discuss Depth of Field and other issues.

I figure this is a good spot to stop today and over the next few days I will continue explaining how a camera phone works.