Remember clicking the shutter release button for the first time? You realized that the camera was a magical device. You just pressed a button and a moment in time was stopped. You viewed the image on your LCD screen and were amazed by the technology.
In truth, though, there’s nothing magical at all about cameras, and understanding the scientific and technological aspects of a camera will improve your photography skills.
The Camera Obscura
While your camera can fit into the palm of your hand, it is considered a dark room, or camera obscura. In a dark room, light enters through a pinhole or a lens. Light from the opposite side of the opening projects an inverted image on a surface in the dark room.
Now here is a quick Physics lesson: rays of light are transmitted in a straight line from their source. For example, if light is coming from the sun, then it is entering the lens at an angle. This light is then altered when it is reflected or absorbed by an object, thus allowing the object to retain the color or brightness of its surface. The lens or pinhole forces the light into the room. When the light is reflected from the top of an object, it courses downwards. If it is coming from the bottom of an object, then the light courses upwards. Therefore, the image that enters the room is inverted. Your eyeballs work on the same principle; however, your brain fixes the inverted image automatically. Your digital camera does the same.
Light has entered the camera, but where does it go? Before modern technology, light reached the film where it created a chemical reaction to make an image. With digital cameras, the light goes to the sensor. The sensor is the soul of a digital camera. If affects many aspects of the image, including the size, resolution, low-light performance, depth of field, and dynamic range.
The sensor is a photosensitive, analog device. It is composed of a specific number of tiny individual sensors called a photosite. There is one photosite for each pixel. For example, my Canon 70D has approximately 20,200,000 photosites or 20.2 megapixels. When light photons hit the photosites, an electrical charge is produced. More photons are collected with brighter light; therefore, a higher electrical charge is generated. Once the exposure is complete, each electrical charge is measured then converted from analog to digital.
With digital cameras, there are two main types of sensors: CCD (Charge-Coupled Device) and CMOS (Complementary Metal Oxide Semiconductor).
To simplify a CCD sensor without using too much technological jargon, this type of sensor’s electrical charge is transmitted to a single amplifier after the photosites have been stored. The charges are transmitted through lines in the sensor and are repeated until all the lines have been amplified and outputted.
This type of sensor produces a higher quality image with better depth of field, less chance of noise, higher resolution, and improved light sensitivity. With that said, this sensor consumes an abundance of power and has a slow processing time.
Photosites in a CMOS sensor contain amplifiers and conduct local processing. This gives the sensor the ability for faster processing. It is also less expensive and consumes less power than a CCD sensor. Nearly all newly produced digital cameras use a CMOS sensor.
These sensors are more susceptible to noise and the light sensitivity seems to be lower than that of a CCD sensor. CMOS sensors are improving and slowly reaching the quality of CCD sensors.
The shutter is a curtain in front the camera’s sensor that opens when the camera fires. It allows light to pass for a determined period. This exposes the sensor to light. A fast shutter would capture less light and decrease the chances of motion blur. A slow shutter would brighten the image; however, you risk capturing a motion blur unless you set the camera on a tripod.
The lens is a vital part of the camera as it focuses and directs incoming light. The lens focal length is measured in millimeters by the distance from the lens’s optical center to the camera’s sensor. The longer the focal length, the smaller the angle of view.
Inside the lens there are interleaved blades that create the aperture. The aperture controls how much light is let in to focus on the image plane. There are between five to nine blades in your lens’s aperture. When shooting in bokeh, or the smoothness of an out-of-focus area, you can determine how many blades your lens has. For example, seven blades would create hexagonal bokeh shapes. Motors in the lens move this element so that the autofocus system can focus on the image.
To summarize, there are multiple technologies in your camera working together to develop an image. It is not just a magical device. The camera is a miniature room which light passes through via the lens, and this light then hits the sensor when the shutter is open.