AG Photo luxury
How it is made a reflex camera
Introduction
In this important chapter I will try to explain how the DSLR cameras (digital single lens reflex) are put together and above all how do they work. First let’s see how the external camera body is made and how through the bayonet coupling can be paired with many different lenses. I drew a professional model in order to be able to show the numerous parts that make up a reflex digital camera. Obviously, cheaper models will lack some of the parts. In the orthogonal projection in figure 01, you can see the part on top (see above), the multifunction wheel for adjusting the various settings (to the left), and the rear of the camera (on the right).
01 Orthogonal projection of the reflex digital camera.
Multifunction wheel
Finger wheel of diaphragms
Interchangeable lens
Sled for the external flash or accessories
Secondary display
Wheel of exposure times
Optical viewfinder
Built-in flash
Bayonet coupling for attaching lenses
Connection slots
Main display
Memory card slot
Anatomy of the camera body
A reflex digital camera is made up of various principal components. Inside the camera body there is a reflective mirror able to modify its angle, an image sensor, a signal amplifier, a processor, a pentaprism, the LCD monitor, an optical viewfinder, a memory card and the battery. In figure 02, we can see a schema of it.
02 Anatomy of a reflex digital camera.
Pentaprism
Introduction
The camera
How it is made a Reflex camera
Photographic lenses
Equipment and accessories
Take a picture:
Buyer’s guide
Sensor
Signal amplifier
CPU
Optical viewfinder
Display
Lens
Movable mirror
Autofocus sensor
Shutter
Memory card
Reflex digital cameras get their name from the particular optic system that uses a reflective mirror (hence the name “reflex”) that is mounted in front of the image sensor. The mirror is mounted on a pivot that allows it to rotate. Normally, the mirror covers the sensor and does not allow light to strike it; in this resting position, having a particular angle, channels the light rays that arrive from the lens towards the pentaprism where they are reflected in such a way that displays the image directly in the optical viewfinder (in the right orientation). This is the characteristic that distinguishes reflex digital cameras from the others. Through the optical viewfinder we are able to see exactly what the lens sees without any parallax errors that occur when the viewfinder instead uses its own separate lens of lower quality than the principal. In the resting phase, as you can see in figure 03, the sensor receives no light.
03 Mirror in the resting phase.
04 Mirror in the shooting phase, live view or video mode
When we shoot a photograph, the shutter release button operates the motor that makes the mirror rotate and keeps it raised for the entire exposure time; in this way allows light to reach the image sensor. During the shooting phase, the viewfinder is then darkened in that it does not receive any more light from the lens. In figure 04 we can see the schema of the shooting phase.
Immediately after the shot, the mirror returns to its resting position, again diverting the light rays towards the pentaprism. When we use the “Live view” function, the mirror is always kept in the shooting position in order to allow the sensor to receive the light that generates the image on the display rather than being reflected into the optical viewfinder. While using “Live view”, the viewfinder will be obscured for the entire time that we are using this function.
The lens has the function of capturing the light and making the rays converge on the focal plane. At the point in which the light rays meet, the focal plane will pass. Having passed this point, the rays that cross, and reversing the image (see figure 04). Then the sensor receives the upside-down image (that will then be oriented correctly by the processor or by the mirror and the pentaprism). In the shot phase, the light reaches the sensor that converts it into an electrical signal. This signal is sent to the amplifier that amplifies it to the corresponding ISO value selected. The signal is then sent to the processor which processes the data, transforming the data to a RAW format image. The image as processed is then sent to the memory to be saved and to the display to be viewed. If we have selected a different format other than RAW, say for example, JPG, then the images are processed, adding filters, white balance and all the other settings selected before the shot and then compressed so that less space is occupied (which would not happen to a RAW image).