The area or region in an image that has to be sharped and fine in contrast as compared to other parts, has to be in focus. A completely focused picture is completely sharped, detailed, well apertured. Similarly, a completely unfocused picture will be completely blurred. Focus also works with integral parts in an image. Focusing on an image is used to bring the viewer’s attention to important elements within the image.
Aperture, light, and an image sensor inside combine to decide about focus. when light enters through an aperture hole, passes/converging through lens, and incidents on an image sensor. Based upon the aperture we selected, if the aperture whole is small like an aperture of f/32 or f/16, all of the rays entering through this tiny hole will concentrate on a shorter part of an image sensor, creating a large part of the image in focus. On the other hand, larger aperture wholes from f/1.4 to f/4 will allow more light to pass in and spread that light onto a wider part of an image sensor creating a smaller depth of field focusing on specific objects within the image
Manual vs Auto Focusing:
Manual focusing is a good practice where we have to adjust our lens by hands, even the camera technology is advanced, still, it can’t read the human mind. So, deciding which part of the image or subject is to be in focus and then adjust your lens according to it will be beneficial. Genres are astronomy, macro photography or stationary objects, etc. where there is low light and the camera could not decide which portion of an image you want to take in focus.
Autofocusing or AF is done by the camera automatically. Inside lens motors and applied AI and software algorithm decides what to focus on. A charge-coupled device (CCD) is used in a typical autofocus sensor. Photographers are free of adjusting the lens to focus for every shot but this practice will not always give considerable results as human perceptions can’t match the integrated AI. Genres include motion subject’s photography like wildlife, sports, etc.
There are three autofocus modes based on the subjects and their motions.
- Auto Focus Single (One-Shot AF or AF-S):
The basic one autofocus option locks the focus on a moving object only once, if the object is continuous to move, you have to set the focus again.
- Auto Focus Continuous (AI Servo or AF-C):
The advanced Auto Focus option puts a continuous focus in a frame on a subject even if it is in a continuous motion but the better AF-C mode depends on camera technology and the movement of the subject with the light conditions.
- Auto Focus Hybrid (AI-Focus AF or AF-A):
A combination of single and continuous Auto Focus modes provides photographers, the option to automatically switch between both modes based on the movement of a subject.