aperture and f-stop are two terms for the same thing: how wide the lens opens to let in light to hit the camera’s sensor. aperture is one of the three aspects of exposure. aperture is both an exposure element and a creative tool. The depth of field it can produce is also dependant on focal length and the distance to the subject. The correct amount of light needed to properly expose your picture can be achieved with many different combinations of f-stop and shutter speed. aperture also controls the depth of field (how much of the picture is in focus). The smaller the lens is open, the sharper the photo’s focus will be from foreground to background. The aperture in the lens is composed of five to fifteen thin, interlocking blades that slide past each other at an angle to control the diameter of the hole. The size of the aperture is measured in F-stops.
F-stops
Common F-stops are:
Although a little counter-intuitive the lower the f-stop number the larger the aperture is. These numbers may seem a little confusing because they seem so random no pattern immediately jumps out at you. f-stop values are determined by the ratio of the focal length of the lens to the diameter of the opening.
f-stop why these numbers
for example lets take a 50mm lens at F/2
Focal Length 50mm/2 = 25
so the diameter of the aperture is 25mm
Now we use the formula for the area of a circle A=Pi*R2
A=3.14159265 * 156.25
A=490.87 mm squared
If you ran these calculations for the next f-stop F/2.8 you get an area of 250.23 mm squared.
So going up one f-stop from F/2 to F/2.8 roughly halved the area of light coming into the lens. So with each f-stop adjustment you can either double or half the amount of light coming into your sensor.
Lenses and aperture
lenses are named for their maximum aperture the smallest f-stop number which is the largest opening. The more light a lens can let in the faster that lens is since you can shoot with higher shutter speeds. The smaller the f-stop the more extreme the bokeh or background blur becomes.
Traditionally older cameras adjusted aperture in full F/stops. Most modern digital cameras allow you to set the aperture steps in 1/2 or 1/3 stops. The sunny 16 rule uses f/16 as its baseline exposure.
The sharpness of a picture is also controlled by the aperture. most modern lenses will produce the sharpest images in the F/5.6 to F/8 range. If you go higher on the f/stop range towards f/22 the sharpness is decreased by diffraction. Diffraction is the spreading of light waves through small openings. If you move towards the lower end towards f/1.4 the sharpness is affected by aberrations. Aberration is a bluring of the image when light from the front of the lens does not converse into a single point. f-stop also has an effect on light fall off on the edges of an image. Wide angle lenses often show a large amount of vignette along the edges at large apertures. F/stop are calculated based on subjects that are an infinite distance away. This is ignored in most photography situations with the exception of macro photography where subjects are much closer to the camera lens. Macro photography uses a more precise working F/stop number.
The accelerati
ng growth curve of light area closely mirrors the escalating price you will pay for lenses with large apertures. These lenses are extremely hard to manufacture which is why You always see the very large aperture lenses as prime lenses. Most zoom lenses only go down to F/2.8. You will also pay more for a fixed F/stop. A zoom lens with a fixed F/stop allows you to set your aperture and it will not change as you zoom. Focusing can be a challenge with large apertures as well. The depth of field becomes quite small, which does not give you a large margin of error. Some extreme aperture lenses include the rare Canon F/0.95 which was made during the 50’s. Also I once read about Director Stanly Kubrick modifying a lens for film that could get F/0.7. Read the full story here.
aperture Priority Mode (AV)
Most digital cameras have an aperture priority mode or AV. This mode allows you to set your desired aperture and the camera will calibrate shutter speed and iso to best match the aperture you need. The camera will base its calculations on the exposure that gives you the fastest shutter speed to minimize blur and camera shake. Understanding aperture will give you some real creative control over your camera and the photos you produce. As a technique it can bring a sense of depth, dimension and mystery into your work.
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