History

• The Konica C35AF, released in 1977, was the first autofocus camera commercially available. The small rangefinder camera used a single beam Honeywell system.
  
  

Two Methods of Measurement

• Two methods are used to calculate focus in the Honeywell system, also known as passive autofocus.
  
  The most widely used focus detection method is phase detection. This is a method by which light is split into two images that are compared for light intensity patterns and a calculation is made between the difference (phase) in these patterns which give exact measurements for focusing the lens.
  
  Contrast measurement is where the intensity difference between pixels is measured on the image sensor. Contrast increases with correct focus so the system finds a focus setting resulting in the highest contrast measurement to ensure the sharpest focus.
  
  

Adding Options

• The first autofocus cameras relied on a single area for detecting focus, making measurements from a single set of split images. This system is effective but a user needed to ensure the measurement area was pointed at the object desired to be in focus.
  
  Multi-beam autofocus uses multiple areas for calculating the correct focus. Instead of a single set of split images being measured, the multi-beam system can have up to 45 seperate areas. On high-end SLRs, each of these areas can be selected as the main point of focus.
  
  

Active System

• An active autofocus method was also created using ultrasonic sound or infrared beams of light which are emitted by the camera to determine the range to the subject. The active system proved unreliable in certain situations (especially focusing through glass or other clear objects) and is no longer the preferred focusing system.