How a reflex is made

1. Objective-is the element that allows the passage of light inside the body of the camera: it consists of one or more lenses that "transmit" the real image of a subject framed on the focal plane (7). The focal plane is the plane placed at a distance for which a lens forms a sharp image: Here is the element (film or sensor) able to record a perfectly defined image

Reflex-Mirror

2. and 3. Mirror-is the mobile element that allows you to frame in the viewfinder the image seen from the lens. Normally The mirror is tilted by 45 ° (2), just to reflect upwards the light that crosses the lens: when you press the shutter release the Mirror rises Up (3) so that you can discover the "sensitive" element, the digital sensor, on which The rays of light incidents will form the image.

4. Pentaprism – is the optical system able to reverse the right with the left (and vice versa) in the image reflected by reflex-Pentaprisma1specchio reflex: In this way, through the viewfinder you can observe a real image and not upside down the Subject framed. For economic reasons many cameras use in place of the pentaprism a system of five mirrors, precisely called Pentaspecchi: it costs less, weighs less, but returns to the eye a less luminous framing, making in some cases more difficult the setting to Manual focus, especially when shooting in low light. However, it Does not affect the quality of the images in any way.

5 Viewfinder. Viewfinder-is the device that allows you to choose and compose the shot. Within the viewfinder, in addition to displaying the framed scene, there are indicators to evaluate the focus and exposure of the subject. The great advantage of the reflex viewfinder is the possibility to frame the scene through the lens itself, being able to see then exactly the image that will form on the sensor. The viewfinder cover is an important factor for the composition of the image: in professional cameras the viewfinder allows a complete view of the framed scene, while in the cheapest products only 90-95% is made visible. Unlike digital compact cameras, DSLRs cannot use the LCD monitor on the back to frame the scene, for the simple reason that the sensor is covered by the mirror; In fact you have managed to circumvent the obstacle with the so-called Live view (the function allows you to see the scene in real time on the LCD screen of the camera). With the development of digital photography was born also a type of electronic viewfinder and have become possible systems non-reflex and without mirror.

Reflex-Shutter

6. Shutter-is the device that allows you to get light to the sensor when you press the shutter button. The shutter can be of two types: central and curtain. In The central shutter there is a series of movable slats placed between the lenses of the lens; They are normally closed and only at the time of shooting they open for the preset time. In the slide shutter, instead, we have two curtains placed near the sensor: when you take the photo, they form a slot that slides all over the sensor, exposing it to the light.

Reflex-Sensor

7. Sensor-is the camera element exposed to light: it is an electronic component that captures images and "translates" them into data to be stored in the memory card. The operation is rather complex: we will see it in a forthcoming article.

8. Diaphragm-is the inner element to the lens through which the light passes that enters the camera before reaching the sensor. It is made up of a set of slats that go to form a small hole of variable amplitude, allowing to dose the amount of light.

9. Path of Light-After having known the essential parts described above, one can understand more clearly how a framed scene can become a photograph. We Follow the Green Line of the figure at the top: the light beams are collected and pass through the lens (with aperture all open) and arrive in the mirror that, inclined at 45 °, reflects them towards the pentaprism which, in turn, "straightens" them and sends them to the viewfinder, Where we square the scene. When We press the shutter release the diaphragm in the lens closes to the diameter we wanted, the mirror rises, the shutter opens for the time we have established and the light beams are deposited on the sensor. On the sensor will form the image, which will be stored then as digital data in the memory card... And here is our photograph.

AND AGAIN...

So Far we have seen the essential parts of the operation of a D-SLR: We add some brief mention to other important elements whose knowledge will come in handy in the following articles.

Shutter-release button - The shutter-release button operates the shutter and the iris: a first slight push of the button allows the focus to be set and the exposure to be read within the viewfinder.

Focus / Focusing screen - The image of objects in front of the lens is formed on the sensor. In general, a photograph is considered technically successful when it has sharpness, ie when it is in perfect focus: the image is sharp only when the distance between the lens and the focal plane is correct. Focusing can be done by turning the appropriate ring on the lens, which causes the lens to move until optimal sharpness is achieved. All the cameras are then equipped with autofocus, with automatic focusing: it will be the internal electric motor, incorporated in the machine or in the lens, to perform all the operations. A focusing screen is made of translucent material, usually frosted glass, which allows us to preview the image framed in a viewfinder. A focusing screen has engraved signs which, varying from model to model, provide help for manual focusing or for aligning the composition.

Exposure meter - In reflex cameras, the exposure meter is TTL (acronym of through the lens, "through the lens"), ie it reads and measures the light that passes through the lenses of the optical system and falls on the sensitive surface.

Sensitivity selector (ISO) - Allows you to set the ISO speed (light sensitivity of the sensor) according to the brightness level of the environment.

Exposure compensation selector - Exposure compensation can increase (brighter) or decrease (darker) the standard exposure set by the camera.

Flash - Most SLRs come with a small built-in flash. There is the possibility of adding an external flash, much more powerful and functional, housing it in the special sled.

Sharpness control - Depth of field is the distance between the nearest and those farthest from the camera within which the image appears sharp. The view through the viewfinder is completely open diaphragm: by pressing this button the aperture closes at the set value and allows you to check the sharpness of the various objects placed on different planes.

Memory card - It is the element that allows to memorize the images, that is the digital data that come from the sensor hit by the light where the image was formed.