A lens (objective) of a camera serves to focus light rays from a scene and project them onto the image sensor. This optical component is formed by a set of internal lenses that use the phenomenon of refraction to conduct light.
The basic structure of a photographic lens
The structure of an objective lens can be divided into internal and external components. Understand the role of each below:
inside the lens
- front element: Collects light from the object and directs it into the lens. It is usually made of resistant material to protect the lens from scratches;
- Diaphragm: controls the aperture of the lens, determining the amount of light that enters the lens;
- focus motor: Adjusts the position of inner elements to focus the image. Lenses can be manual focus or auto focus;
- internal elements: manipulate the light path to direct it to the rear element. They are also responsible for adjusting the sharpness and contrast of the image;
- rear element: is responsible for focusing the light on the surface of the image sensor.
exterior of the lens
- filter ring: allows you to fit external filters to the lens, which can modify colors, saturation or reduce unwanted reflections;
- focus ring: Adjusts the position of the internal lens elements to focus the image. It is usually rotary and can be controlled manually or automatically;
- zoom ring: Adjusts the focal length of the lens to get an image closer or farther from the subject. This feature is present only on optical zoom lenses;
- opening ring: Allows you to control the lens aperture to adjust the amount of light entering the camera. Aperture affects depth of field, allowing you to blur the background of the image and highlight the main subject;
- lens mount: Allows you to attach the lens to the camera body. There are several types of mounts, such as Canon EF-S, Nikon F-mount and Sony E-mount, each compatible with a specific camera make and model;
- stabilization controls: Some lens models may have optical stabilization, which helps reduce shake and blur in images captured in low light or high magnification situations.
Focal length and field of view
A focal distance of a lens, measured in millimeters (mm), is the distance between the optical center of the lens and the image sensor. The optical center of the lens is the point where light rays converge to form a sharp image. In general, lenses with a longer focal length are longer.
The longer the focal length of a lens, the further it can see. An 18-55mm lens, for example, is a lens with approximately 3x optical zoom, as its maximum focal length (55mm) is three times the minimum (18mm). As you rotate the zoom ring, the elements inside move to change the optical center.
O field of vision of a lens is the angle in degrees that the objective can see. It is inversely proportional to the focal length. An 18 mm lens, for example, can see 64 degrees horizontally on an APS-C camerabut only 23 degrees at the 55mm focal length.
Fixed vs Zoom lenses
In general, lenses can be classified as fixed or zoom. The differences are:
- fixed lens: It has a single focal length and a fixed angle of view. Also known as a prime lens, it does not have the ability to enlarge the image, but it usually offers superior image quality and a larger aperture;
- zoom lens: It has a variable focal length, which allows the photographer to enlarge or reduce the image without having to change lenses. It is more versatile, but may have lower image quality than fixed lenses due to the greater number of internal elements required to allow for focal length variation.
Lens types and applications
We have an article that compares the main lens types found on smartphones and cameras. Briefly, we can classify them as:
- Wide-angle (wide) lens: Is used to capture a wider area, such as landscapes, architecture, and interior spaces. It has a wider angle of view and a greater depth of field, which makes objects sharper than with telephoto lenses. It is versatile and common in smartphones;
- ultrawide lens: is similar to wide angle, but with an even wider viewing angle. This lens is ideal for capturing panoramic landscapes and wide environments. One downside is that images can have distortions around the edges, such as the fisheye effect;
- Telephoto lens (telephoto): is used to zoom in on distant objects, such as sports scenes and wildlife. It has a longer focal length, which allows for greater optical zoom. It has shallower depth of field, making it easier to blur the background. However, it can be heavier and more expensive;
- macro lens: Used for shooting close-up subjects such as flowers, insects, and small objects. It has a very short focal length and shallow depth of field, allowing the photographer to capture minute details;
- periscope lens: is found on some cell phones and allows for greater optical zoom without increasing the size of the lens. The elements are positioned horizontally within the fixture and require a mirror to deflect light onto the sensor. It’s more versatile than the telephoto lens, but it can lose sharpness.
Lens and image resolution
Lens quality is influenced by factors such as aperture, distortion, and aberrations, which can affect image sharpness and clarity. Therefore, a higher resolution camera sensor alone does not guarantee more detailed images.
Good quality lenses usually offer higher resolution, minimizing these problems and resulting in sharper images. In addition, the lens opening directly influences the amount of light that is captured, which requires lower ISO sensitivity and tends to generate less noise on the image sensor.
Lens aberrations and distortions
Lens aberrations are imperfections that affect the quality of the image captured by the camera. There are two main types of lens aberrations:
- chromatic aberrations: occur when the different colors of light do not focus on the same focal point, causing colored halos in the image;
- spherical aberrations: Occur when light rays are not refracted correctly as they pass through the lens surface, causing a loss of sharpness at the edges of the image.
Lens distortions are another type of imperfection that affects image quality by causing geometric or perspective changes. Distortions can be of two types:
- barrel type (barrel): when the image is curved outwards, that is, the center of the image appears to be enlarged more than the edges. It is usually found in wide-angle type lenses;
- cushion type (pincushion): when the image is curved inwards, that is, the edges of the image appear to be more enlarged than the center. It is usually found on telephoto lenses.
Aberrations and distortions can be corrected with image editing software or in-camera adjustments. When possible, the best solution is to buy a higher quality lens that minimizes the need for post-processing corrections.
Common questions
Use a soft brush or blower to remove any dust on the surface. Afterwards, if there are grease marks, you can use a microfiber cloth to clean the camera lens. The use of isopropyl alcohol or ammonia solutions not recommended by manufacturers as it may damage the lens coating.
The camera lens is spherical to allow light to be collected more efficiently from all directions. In addition, the tubular shape of the lenses is the most practical to handle and the cheapest to produce. However, most image sensors are rectangular, so photos are not round.
