Aperture priority mode
Perhaps this is the most used and most useful mode on the Dslr camera. To set the Dslr camera to aperture priority mode, must turn the dial at the left top part of the camera to A or Av. At this mode you can choose aperture and the camera calculates the shutter speed for proper images.
Ok, ok but what is the aperture ?
Aperture is the hole on the lens, where the light enters the camera. It can be regulated to be bigger or smaller. Aperture is noted with a number, usually from 1 to 32. Lenses usually noted with their brightest (biggest aperture) for example 100mm f/2.8. The f/2.8 (or referred 2.8) is the lens‘s brightest possible aperture. Aperture can be regulated on the lens, but usually you cannot see just on older lenses with a dedicated aperture ring, because newer digital lenses usually only regulate aperture at the very moment when the picture is taken, otherwise the aperture is always open at the widest setting. In older lenses you actually see the hole will be smaller when you turn the ring.
Small aperture f/22 the whole is small, every stop the whole are will be double, f/16 double, f/11 double, f/8, f/5.6 f/4 f/2.8 f/2 f/1.4 f/1. The f/1 aperture is a really big hole, only brightest lenses has this big aperture. F/1.4 is more common.
How to learn the lens brightest aperture?
The lenses are usually defined with two numbers: the focal length and brightest aperture. For example Canon 60mm f/2.8 Macro. The f/2.8 refers to aperture. Zoom lenses defined with two numbers: 24-105mm f/4. In this case the lens has f/4 constant bright aperture at both end of the zoom range at wide angle and telephoto settings as well. Most zoom lenses has different aperture settings at the two end of the zoom range, for example 18-55mm f/3.5-5.6 this means that wide end has f/3.5 aperture, the long end f/5.6 (usually telephoto lenses with the same size glass let less light in)
Aperture does two things:
1. regulate the light amount into the camera
2. and control depth of field, or other words how many part of the image is in focus.
If we use smaller apertures(smaller hole, bigger number like f/11-f/16) the amount of focus is bigger, if we use bigger aperture(smaller number f/1.8-f/2.8) smaller parts of the image in focus, preferred for portraits, the background and foreground is more blurred.
Lets speak about different types of lenses and apertures.
1. Wide angle lenses – focal length of 30mm and smaller.
Here usually almost everything is in focus, for wider lenses more so. There are two differences, first if we make pictures of very close subject, and if we want to have a picture that is sharp in a long distance and very close as well (for example dramatic landscapes on a hilltop for example). Usually the sharpest or smaller apertures to selected for landscapes (f/5.6-f/16)
2. Telephoto lenses – 100mm-800mm
This lenses blur the background anyway we usually use the sharpest settings to have the best output, if the subject is closer we can use bigger apertures as well, as we like to control the depth of field.
3. Macro lenses usually 60-180mm but used for very close focusing
Here we can choose the aperture, but if we want more portion of the focus we usually use small apertures of f/8-f/22.
In reality the best is to experiment and look the results to understand what picture you like to take.
If you turn the main dial to Av, and after turn the front dial you see numbers changing from f/2.8 or f/3.5 or f/5.6 to usually f/22 or f/32.
How to choose aperture setting?
If we want the background blurred and high shutter speed we usually use bigger or brighter apertures (smaller number f/1-f/2.8-f/4). If we want more things in focus for example for macro or landscapes we use smaller apertures(f/8-f/22). The thing is not so easy though because the lens is usually not the sharpest at bigger apertures this way we use little smaller apertures to have sharp pictures especially for telephoto lenses.
Image sharpness is also depend on aperture. The sharpest apertures are usually between f/4 and f/8 on any lens, this often referred as sweet spot of the lens.
If you really want to learn do the assignment. Make pictures with different apertures from the biggest(smaller number) to the smallest apertures. Study the pictures you make.