Tip of the week: Photography basics - Aperture

Continuing our photography basics tips, today we are talking about the aperture. I will explain its meaning in terms of photography and in terms of lens and optics. For the readers who missed my introduction to photography basics, you can check it before reading this text:

Photography basics - Exposure

Physics behind the aperture

Since it is necessary for the light to hit the sensor to create a photograph, we need to control the amount of light that falls on the sensor during the exposure. We can do it in a very simple way, by changing the opening in the lens through which the light goes through the optic elements towards the sensor. That opening is called APERTURE. It is a diaphragm that consist of blades which can be adjusted so the opening changes in diameter. The same principle as in the iris of an eye. So the greater the opening, the more light will fall onto a sensor and vice versa. The aperture can be controlled either directly on the camera, or on the lens aperture ring, depending of the type of a lens and a camera. In most modern lenses, there is no aperture ring, so the camera controls the aperture value. Diaphragm is located on the bottom part of the lens, close to the camera mount.

Aperture Scale

Aperture values are given with f-number. F-number is just a ratio of focal length and aperture diameter. The lower the f-number, the more light goes through the lens onto a sensor, the greater the f-number, less light falls onto a sensor. F-number has discrete values that can be set by the lens or the camera and are called aperture stops (f-stop). Each one f-stop is a square root of number 2 of the previous f-stop (f/1, f/1.4, f/2, f/2.8, f/4, f/5.6, f/8,…) Difference in therm of light intensity between one f-stops is double. So at f/1.4, the amount of light that reaches the sensor is 2 times more than it would fall at f/2. Lenses can also use fractions of one f-stop values such as (f/1.2, f/1.8, f/2.2, f/3.5,…). Lenses with low f-number (wider apertures) are called "fast" lenses and are usually more expensive. Fastest lenses can achieve apertures such as f/1.4 and f/1.8, and in rare cases f/1 and even f/0.95.

Closeup on reflex camera top lcd display with f-stop indication

Aperture in photography

Changing the aperture does not only change the amount of light, but also changes the depth of field. Faster lenses can have very narrow depth of field using low f-numbers and can easily separate the subject from the background, so the background looks blurry. Low f-numbers are often used in portrait photography but can also be used whenever you need to have narrow depth of field. Higher numbers are usually used in macro landscape photography because in most cases, we need all parts of the frame to be in focus. These are not rules, you can explore yourself and find the depth of field which works best for a certain frame. We need to mention that the distance between the subject you focus on and the camera also changes the depth of field. The closer the camera is to the subject, the narrower depth of field is, at the same aperture value. So you can use both the aperture and distance from the subject to play with the depth of field.

Closeup aperture blades

And few advices…

Faster lenses usually have better image quality and are more expensive. Also they are more bulky, especially the lenses for full frame cameras with focal length higher than 100mm, because they need larger optical elements (lenses) to achieve wider apertures. If you need to travel light, you might consider using cameras with APS-C sensors because their lenses tend to be smaller comparing to their full frame counterparts with the same widest aperture. Of course you might be sacrificing some image quality if you go for the APS-C comparing to full frame cameras. If you are into night and astrophotography wide aperture lenses are a must have.

Photo credits: Norgal, Francesco Maltinti, Tea.

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October 17, 2019


Thank you! There always need to refresh the main knowledge

October 16, 2019


Once again a great article! Going to pass it on to my daughter who is taking up photography. William 

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