In recent years digital cameras have gotten so cheap that almost anyone can afford one. But how do they work? How is the light converted into images inside a digital camera? What are the secrets of the digital images? What is the resolution of an image? What is the difference between a picture saved in .jpg and a picture saved in .tiff?
This is not a guide to using digital cameras. Probably, with so many existing devices, all with their peculiarities, no one can’t write that, an universal guide for using digital cameras. For that, you have the user’s manual available for every camera you buy. Sometimes, when you buy second-hand items, you might not get an user’s manual, but they are downloadable from the Internet and usually they are free.
The article would, instead, is a brief foray into the world of digital photography, explaining those concepts which we believe will be useful for amateur photographers to obtain better photos and a better understanding of the concepts encountered when they want to process photos with specific programs such as Photoshop.
How does a digital camera work? Although digital, it has much in common with the analog camera with film. It uses an objective, shuttered systems, viewfinders and focusing or targeting systems. It differs in how it captures, stores and processes photographic images.
Digital cameras use image sensors to save the original picture. The image sensor performs the transformation of the image into an electrical signal that is, at its turn, transformed into a digital signal through which the information is stored on a storage medium (memory card).
There are two types of image sensors:
::: CCD – charge-couple device (for which it was awarded the Nobel Prize for Physics in 2009) and
::: CMOS – complementary metal oxide semiconductor.
What is the difference between the two types of sensors?
::: CCD sensors create high quality images with less noise, but the data read speed is lower than at the CMOS sensors;
::: The light sensitivity of the CMOS sensors is lower, but they consume less energy, so the cameras have a longer life for their batteries in the device;
::: CMOS sensors use the traditional technology of chip manufacturing, so they are cheaper than CCD sensors, which are manufactured using a special technology, which involves higher costs.
Recently it was developed a new technology called sCMOS, trying to use the advantages offered by each of the two technologies above CCD and CMOS.
The image sensor works with an image processor. The latter takes an analog signal from the image sensor, converts it into digital signal (in bits – strings of 0 and 1), the digital signal, a carrier of information about the image captured with the camera, is then stored on a memory card.
The structure of a camera is presented next. Whether a digital camera or a classical one, they essentially have the following components: Objective; Shuttered system ; Targeting system.
The objective is a converging and diverging lens group, grouped in different ways, so the resulting image to have a very good quality. The main parameters of an object are: focal length (f) and relative openness.
The focal length is the distance between the center (point where the converging rays meet; they are reflected or refracted by an optical system) and the lens plane. The focal length is measured in millimeters. The lower it is, the bigger will be the visual area of coverage.
The relative openness is the ratio of the focal length and the maximum diameter of the opening of the objective, f: = f / D ≥ 1. If the opening is close to 1, then the brightness of the objective is better.
In classical objectives there are two adjustable parameters: the ring of the distances – to control the image quality and the aperture ring – to control the diameter of the light passing through the target. At the objectives that allow zooming, there is a ring that allows changing the focal length.
When talking about digital cameras all these parameters are adjusted automatically by the software, so that the users should not even bother with adjustments. But professional photographers know these details and use them to their advantage, managing to achieve high visual impact images.
The aperture or the diaphragm is another important element of a digital camera. The diaphragm opening control means controlling the amount of light that will “impress” the film or the image sensor. Using the camera, you probably have noticed the following inscriptions: f: 2, f: 2.8; 4; 5; 6; 8; 11; 16 or 22. What these values?
The relative openings of the aperture f: 2 correspond to the maximum aperture opening and f: 22 indicates that the diaphragm is closed. Switching from one indication to another, for example from f: 2 to f: 2.8, shows halving surface of the aperture’s opening.
The depth of the objective represents the area in front and behind the target object where the background elements have an acceptable clarity. The depth of the objective increases with the closure of the diaphragm and decreases when the object of the photo is too close to the camera and with the increasing of the focal length of the objective.
The shuttered system ensures the control of the camera to light the image sensor (or the film, if the device is a classic one). The range of exposure times (the times when the aperture is open and the light is allowed to enter the device) is very wide, the technology progress bringing with it very small times (ten thousandth part of a second) or very large times (a few minutes).
The targeting system allows the control of the camera for taking the correct photo of the subject. It also helps to control the image clarity. Digital cameras allow both targeting the subject using a display (LCD screen) and also using the classical way, through a viewfinder.
In my next article I will talk the discuss about the same subject, the difference being that the article is supposed to be a continuation of that presented here today. I will talk about themes like exposure to the light and how many pixels does a resolution must have in order to consider the camera taking high-definition photos.
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