What is Fisheye Lens?
A Fisheye lens is an ultra wide angle lens that is used to produce strong visual distortions and create a wide panoramic view. Fisheye lenses can achieve extremely wide angles of view. Instead of producing straight line images (or rectilinear images), the fisheye lenses produce a characteristic convex image (non-rectilinear image) by using a special mapping angle (equisolid angle).
An American physicist and inventor Robert Wood coined the term fish eye in 1906. Wood studied how a fish can view an ultrawide hemispherical view from underwater (a phenomenon known as Snell's window).
Fisheye lenses were first used in the 1920s for meteorological purposes to study the formation of clouds. The lenses were called "whole-sky lenses." The fisheye lens usually has an angle of view between 100 to 180 degrees. The focal length of the lens depends on the film format.
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Types of Fisheye Lens
There are mainly two types of fisheye lenses; Circular fisheye lens and Full-frame fisheye lens. They produce very different results.
1. Circular Fisheye
Circular fisheye lenses are used to capture a view angle of 180 degrees or larger, the image is projected as a circle within the frame. The image produced is highly distorted; distortion depends on the distance of the object from the lens and the structure in which it is located.
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2. Full-frame Fisheye
Full-frame fisheye lenses produce an enlarged image circle that covers the image frame entirely. That's why the picture angle generated by this lens measures 180 degrees when measured from one corner to another corner. It is the most common type of fisheye used by photographers.
What is a Fisheye Lens used for?
A fisheye lens is designed to capture very wide-angle images, usually an image of 180 degrees. They are primarily used for landscape, artistic photography, and extreme sports.
Here are some of the benefits of the Fisheye Lens:
1. Distortion
Distortion is annoying a lot of times, but not always. Distortion is an advantage for the fisheye. Find views where the fisheye effect adds beauty to the scene. When it is used rightly, the fisheye distortion effect is pleasing to the eyes and can be preferred for a wide-angle lens.
2. Point it up
If you point the fisheye lens towards the sky or just partly upwards (by keeping ground in a still frame), you can get some crazy good-looking views.
In this case, the fisheye lens is used to get a super-wide view when it is pointed upwards.
3. You can use them on Portraits
You can make an extreme wide-angle selfish by using a fisheye lens. Note that you should not keep the object close to the edge, or it will get distorted.
4. Creativity
A fisheye lens is able to create some images which are not possible by using normal lenses. You can use a fisheye lens on your camera for a more extended timespan and find engaging and creative image views by pointing it everywhere.
Fisheye Lens Projection
In a fisheye projection, the distance between the point and center of the image is proportional to the true angle of separation.
The fisheye projections are not single but occur in a group of transformation projections that are named differently by manufacturers like equisolid angle projection, equidistant fisheye projection, etc.
The traditional spherical projections like orthographic or stereographic projections over circular images are not common these days. Panorama tools are there to capture views of such projections.
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(This is a Circular Fisheye projection)
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(The image mentioned above is a Full-frame Fisheye projection)
Characteristics of Fisheye Lens
These are the characteristics of a fisheye lens:
Focal Length: A standard fisheye lens has a focal length of 8 mm to 10 mm, and a full-frame lens has a focal length of 15 mm to 16 mm.
The Angle of View: The angle of view of a commonly used fisheye lens is 180° at its widest point.
Image Distortion: The distortion of the image formed from the fisheye lens is called barrel distortion. In barrel distortion, the central part of the frame appears to bulge outwards, and due to this, the image produced is called a curvilinear image.
Depth of Field: Due to the extreme wide-angle, the depth of field of a fisheye lens is also considerable.
Applications of Fisheye Lens
Here are some of the applications of the fisheye lens.
The fisheye lenses are used in extreme sport, artistic photography, and landscape.
Fisheye Lens is used in planetariums for night sky projections. The projects are also useful for making digital contents in the interior part of the room.
Fisheye Lens is used by Visual combat simulators and flight simulators to monitor and control the air traffic, thereby making it easier to train military personnel.
Fisheye Lens is used by resource managers and scientists for hemispherical photography.
Fisheye Lens is used by astronomers to capture light pollution data and cloud cover.
Videographers and photographers use fisheye lenses to take motion shots. For example, while riding, these lenses are used to focus on the bike and the rider.
Fisheye Lens is used in computer graphics to create environment maps from the physical world.
FAQs on Fisheye Lens
1. What is a fisheye lens and what is its main purpose?
A fisheye lens is an ultra-wide-angle lens that produces strong visual distortion to create a wide, hemispherical, or panoramic image. Its main purpose is to capture an extremely wide field of view (FOV), typically 180 degrees or more. This allows photographers and scientists to capture vast scenes, such as entire landscapes or architectural interiors, in a single frame, which is impossible with a standard lens.
2. How does a fisheye lens work to capture such a wide angle?
A fisheye lens works by using a unique assembly of highly curved glass elements. The front element is extremely convex, allowing it to bend light from a very wide angle and project it onto the camera's flat sensor. Unlike a standard lens that aims to correct distortion, a fisheye lens intentionally creates it. This process, known as equisolid angle projection, maps the wide scene into a characteristically distorted image, embracing the curvature.
3. What is the main difference between a fisheye lens and a standard wide-angle lens?
The primary difference lies in how they handle distortion. A standard wide-angle lens is rectilinear, meaning it is designed to render straight lines in a scene as straight lines in the final image. In contrast, a fisheye lens is curvilinear; it does not correct for distortion, causing straight lines that don't pass through the image centre to bend, creating a convex effect known as barrel distortion.
4. What are some common real-world applications of a fisheye lens?
Due to their unique wide-angle view, fisheye lenses are used in various fields:
- Photography and Cinematography: For creating artistic, distorted effects and capturing expansive scenes or tight interior shots.
- Security and Surveillance: A single CCTV camera with a fisheye lens can monitor a wide area like an entire room, eliminating blind spots.
- Action Cameras: Brands like GoPro use fisheye lenses to capture immersive, first-person-view footage in sports.
- Scientific Research: Used in meteorology to capture cloud patterns (whole-sky cameras) and in architecture to document building interiors.
5. What are the typical focal lengths for a fisheye lens?
A fisheye lens has a very short focal length. For full-frame cameras (equivalent to 35mm film), typical focal lengths range from 8mm to 16mm. Shorter focal lengths (e.g., 8mm) usually produce a distinct circular image within the rectangular frame, while longer ones (e.g., 15mm-16mm) produce a 'full-frame' fisheye image that covers the entire sensor area.
6. Why does a fisheye lens produce a distorted image instead of a realistic one?
The distortion is an intentional design trade-off. To map a 180-degree hemispherical view onto a flat sensor, the lens must compress the visual information, especially at the edges. A realistic (rectilinear) lens would require an infinitely large sensor to do this. The fisheye lens solves this by compressing the periphery of the image more than the centre, which results in extreme barrel distortion. This effect is not a flaw but the very feature that allows it to achieve its ultra-wide perspective.
7. Can the fisheye effect be corrected or removed from a photo?
Yes, the distortion from a fisheye lens can be corrected using software in a process called 'de-fishing'. Photo editing programs can apply algorithms to remap the pixels, straightening the curved lines and converting the curvilinear image into a standard rectilinear one. However, this process involves stretching the image, especially at the corners, which can sometimes result in a loss of sharpness and detail in those areas.
8. How does the image from a fisheye lens differ from what is formed by a simple convex lens studied in ray optics?
While both are converging lens systems, their complexity and goals are fundamentally different. A simple convex lens, as per basic ray optics, is meant to form a predictable image with minimal aberrations over a narrow field of view. In contrast, a fisheye lens is a complex multi-element system designed to manage a massive field of view. The extreme barrel distortion that defines a fisheye lens is considered a severe aberration in a simple lens but is the primary intended feature of a fisheye.
