Focus speed
In photography, focusing speed is the length of time an autofocus system takes between the initiation of the AF process by the photographer and the determination of the focus point by the camera electronics. The focus speed is determined by various factors internal to the camera as well as various external factors.
Influencing factors
- The focusing speed is influenced by
- the type of AF system (phase detection AF, contrast AF, hybrid AF)
- the type of AF sensors (cross, line or pixel sensors)
- the light intensity of the optics of the AF module and the lens used
- the speed of internal processing by the camera electronics
- the mass and number of the mechanically moved elements, i.e. lenses in the optical system
- the performance of the autofocus motor
- the translation of the mechanics (with older lenses) and the response behavior of the lens electronics
- the focal length of the lens
- Auxiliary functions of AF (e.g. infrared AF auxiliary light or hybrid AF)
- AF mode of camera AF (single (picture) AF, continuous AF)
- Electrical voltage of the camera battery
In general, the contrast AF used in most compact digital cameras and smartphones is slower than a phase detection AF of an SLR camera. Newer models, especially many mirrorless system cameras, integrate a fast phase AF directly on the recording sensor.
Externally, the subject and the recording situation as a whole are decisive for the effective focusing speed ; The following factors play a role here:
- Object or motif contrast
- Position of the object or the speed as a change in the vertical distance to the camera
- Illuminance or measured light value of the subject or object to be measured (surrounding light situation)
Typical problem situations
The autofocus can have difficulties in extreme light situations such as backlighting , taking pictures with little available light or with very high brightness, etc.; Objects with a low subject contrast can often only be focused reliably with a cross sensor , with active distance measurement or with the help of an AF auxiliary light . When moving quickly to the vertical axis of the camera at a short distance, the ability of the AF system to track the focus and track the subject is important.
Possible solutions
Instead of the fully automatic selection of the active focus point by the camera electronics, the central focus point can be preselected with many cameras, which enables pre-focusing on the desired focus point of the subject and subsequent pivoting and alignment of the camera to the desired subject content.
The photographer can avoid problems with insufficient focusing speed by focusing manually.
If you have too little practice in manual focusing or if you have to work with an electronic viewfinder (EVF) on a digital camera, you can make do with pre- focusing in many cases : To do this, an object is focused on approximately the same distance and the focus is independent of the exposure saved for the next trip.
Cameras without a cross sensor focus unreliably or sometimes not at all with certain streaky subjects; A simple rotation of the camera by 45 to 90 degrees with focus storage and subsequent correction of the subject detail helps here.