CamCyclopedia
Contents
- Basic description and phenomenon related to lens
- Galaxy camera lens
- Notes
Basic description and phenomenon related to lens
[1] What is a lens?
A lens is an optical tool that focuses light rays reflected off a subject to form its image on the image-sensor. The lenses used in smartphone cameras are made of either plastic or glass.
[2-1] Principle of lens
When a light ray passes through two mediums with different refractive indexes, some part of it gets reflected and some refracted. This refers to Snell’s law. Similarly, when a light ray passing through a lens is refracted, this refraction forms a focal point on the image sensor to create an image. This is a basic yet important phenomenon.
According to this law, the focal point of a convex lens forms behind it and that of a concave lens, in front of it. These lenses are combined to form a group, and the distance and focus between these groups are adjusted to form an image on the sensor.
The below double gauss lens is illustrated with a series of examples [1]. This is one of the lens combinations commonly used in cameras.
[2-2] Explanation of the terminology
1. Depth
Depth is the range of distance between the subject and the camera at which the subject becomes clear.
Depth can be mainly divided into Depth of field and Depth of focus. Depth of field is a range where the periphery of the object in focus is clear. Depth of focus is the sensor motion range within which a fixed subject won’t go out of focus.
We usually qualify depth as ‘shallow’ or ‘deep’. The range of sharpness/clarity is extremely narrow in shallow depth and extremely broad in high depth or ‘deep’ depth.
Depth and sharpness are very closely related. Short-range shooting results in background blur as a side effect of size reduction, given the limitations of mobile lenses.
The picture gets blurry because the focal point of the periphery differs from the center because of a shallow depth of field lens or growth in sensor size. In this case, distance the camera and the subject to keep the minimum focus intact. This will make for a sharper photo if you are taking a picture using the zoom feature.
2. Aperture
The aperture changes the effective diameter of the lens. The aperture can adjust the amount of light filtering through the lens and can also control the depth.
The wider the aperture the more the amount of light that comes in and the shallower the depth gets. The tighter the aperture the lesser the amount of light that comes in and the more the depth of the picture. Galaxy cameras have a fixed type aperture.
3. F-number
4. Angle of view
As the name suggests angle of view is the angle at which the camera can capture an image through the lens. The angle of view is the angle of the light ray diagonal to the image sensor. Usually, the angle of view on a telescopic camera is narrower than on an optical camera.
5. MTF (Modulation Transfer Function)
In general, as the spatial frequency rises, the contrast becomes imprecise, resulting in a lower modulation transfer function value. The modulation transfer function is an important indicator of performance in lens design.
[3] Lens phenomena
- Vignetting
Vignetting is a phenomenon where the amount of light near the perimeter decreases compared to the center, causing the picture to become darker. The light intensity decreases towards the periphery due to the Cosine 4th rule [2].
Vignetting is corrected by a process called LSC (Lens Shading Correction) in the ISP (Image Signal Processor) of a smartphone. Sometimes, vignetting is deliberately applied to a picture via post-edit to focus on the subject.
- Flare
3. Distortion
- Optical distortion
Optical Distortion or TV Distortion is one of the many aberrations resulting from the characteristics of lens design. The distortions shown above are Barrel Distortion or Pincushion Distortion. Lens distortions such as these are corrected by a process known as LDC (Lens Distortion Correction).
- Perspective distortion
Perspective Distortion is a distortion in perception when 3-D shapes are captured as 2-D. This gets especially worse when the angle of view is wide or when the subject is large. The reasons behind perspective distortion are different from that of optical distortion, and it can take place even in the absence of optical distortion.
Galaxy camera lens
Configuration of the lens module
The Galaxy camera is divided into viewing angle lenses preferred by the consumer. It is typically made up of ultra-wide, wide and telephoto lenses. However, these days, Galaxy S Ultra models come equipped with an additional high-power zoom telephoto lens that uses prisms (limited to Ultra models). This prism using a high zoom telephoto camera folds the path of the light to take sharper tele pictures while avoiding the ‘camera bump’.
Super-Clear Window
Super-Clear Window is the both-side anti-reflective coating on the camera window glass, unlike the previous one-sided anti-reflective coating. Even the window glass can lead to a flare or ghosting, but applying this technology reduces the rate of reflection thereby preventing ghosting. This allows you to click relatively clearer pictures in a dim environment.
Nano-structure coating
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Notes
[1] Double Gauss Lens: https://en.wikipedia.org/wiki/File:Double_gauss.png
[2] Cosine 4th rule: Douglas A. Kerr, P.E. (2007). Derivation of the “Cosine Fourth” Law for Falloff of Illuminance Across a Camera Image
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