Camera Basics #14 - Difference between contrast autofocus, phase autofocus and hybrid autofocus
Autofocus does a lot of work for us photographers; of course, there are also purists who like to focus manually. But let's take a look at how the different autofocus models work: Edge contrast autofocus, phase comparison autofocus and hybrid autofocus.
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Edge contrast autofocus
With contrast-based focusing, the autofocus is tested by trying out different focal planes. The glass of the lens is moved until the brightness gradient of light and dark edges reaches maximum agreement.
The camera must receive the same measurement at least twice before the focus is finally determined. This is to ensure that the focus is actually calculated correctly. This method is quite inexpensive to install, which is why it was used for a long time in video and compact cameras.
Advantages of contrast autofocus
- strong low light autofocus performance
- can recognize and track structures and shapes
- reliable detection and focusing of faces
Disadvantages of contrast autofocus
- often focuses past the object
- not good focus performance with moving objects
- slow focus speed
Phase comparison autofocus
Phase comparison autofocus is in itself an older system than contrast-based autofocus, but it is partly applied to the sensor. In contrast to contrast autofocus, this system is more of a performance-saving system. This system recognizes the direction in which the autofocus must focus in the first step. This is done by creating comparable light intensity patterns, whereby the line and cross sensors help. It is important to understand that the autofocus performance depends on the amount of exposed sensors: The wider the aperture is closed, the less light the sensors receive. In this case, it is an advantage if the camera has more sensors.
Advantages of phase autofocus
- high accuracy
- fast focus performance
- can track movements better
- faster due to the calculation of direction and distance information
- predictive focus - it calculates the required position at the time of shooting
Disadvantages
- weak low light AF performance
- Measurements only possible in AF fields
Hybrid autofocus
Hybrid autofocus combines both contrast autofocus and phase comparison autofocus. It is often also called phase hybrid autofocus. This system utilizes the advantages of both systems and allows them to work together perfectly.
First, the object is determined by the light intensity patterns, followed by fine tuning via the contrast autofocus. Hybrid focus systems are able to partially switch their function, so that a phase autofocus not only remains a phase autofocus alone, but also switches to a contrast autofocus point.
Advantages of hybrid autofocus
- better low light autofocus performance
- fast focusing
- good motion tracking
- high accuracy
What role does AI play?
Anyone who demonizes AI is losing out on huge potential, especially when it comes to autofocus systems. These systems benefit greatly from AI, as it helps to recognize objects and precisely define their position in three-dimensional space. Sony, for example, creates a skeleton of the object to define exactly how it relates to the camera in the image. In this way, the camera knows whether the eye is turned to or away from the camera.
What role do lenses play?
Lenses can offer advantages or disadvantages depending on the focus system. The built-in focus motors play an important role in the performance of the autofocus. Linear autofocus is advantageous compared to hybrid autofocus, as it does not produce strong focus breathing, which makes the image unsteady when recording video. When focusing, the aperture determines how much light falls on the sensor, so depending on this, the shadow of the aperture covers the cross sensors of your camera's focus system.
Tip for backlit shots
If you want to take great backlit shots and have problems with the autofocus, you can hold your hand in front of the sun to make focusing easier. Once the camera has focused, all you have to do is quickly pull your hand away from the lens.
Conclusion
The focus systems have now achieved very good performance. You can almost always trust them without hesitation. Especially with the introduction of hybrid autofocus, focusing is now not only fast, but also particularly reliable. However, even today there is certainly still potential that could be exploited. Especially in the development of faster motors and the expansion of hardware support systems.
Nikon Z8 Body
Fujifilm
Panasonic Lumix DC-S9
OM SYSTEM OM-1 II Body
Nikon Z6 III Housing
A little task for you:
Play around with different lighting situations to get to know your autofocus better. This will give you more confidence in your camera and help you deal with stressful situations.
Show us your pictures on Instagram and/or Facebook and tag us @fotokochde! We look forward to seeing your results!
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