What is a camera reflex

The name of a reflex camera comes from the fact that these types of cameras use a mirror that reflects ( reflex ) the light coming from the scene and directs it towards the viewfinder (towards the photographer’s eye).

When the shot occurs, the mirror is raised , that is, rotated upwards so that light can reach the electronic sensor (or the film in the case of analog SLR cameras).

Once the mirror is raised, the shutter opens for a time determined by the photographer, to let the correct amount of light pass through.

That light reaches the electronic sensor and is transformed first into an electrical signal and then into a digital value (a number that indicates how bright each point in the image is).

In a SLR, the scene seen by the photographer through the optical viewfinder is the same as the one the camera will take, there are no parallax errors , since both the sensor and the viewfinder visualize exactly the same frame from the same point of view (both collect light coming through the lens).

In all cameras, the image that reaches the sensor is inverted with respect to the scene (the top goes down and the bottom goes up).

For the photographer to see the scene correctly, the optical viewfinder uses a pentaprism or a pentamirror with which the image arriving from the lens is reversed 180º .

The pentaprism mechanism is what gives it that hump or bulge look on top of SLR cameras.

Digital SLR cameras are practically the same as analog (film SLR) when it comes to optics and mechanics.

Features of a reflex camera

The main characteristic of a reflex camera is the one we have discussed: it uses a mirror to get the image from the lens to the optical viewfinder.

At present, what is known as SLR is the digital version: digital SLR camera . In English, they are called DSLR : Digital Single Lens Reflex.

On the other hand would be the film reflex cameras or analog reflex cameras. In English it would be SLR ( Single Lens Reflex ).

Let’s see some characteristics that all digital SLR cameras usually have in common:

Optical viewfinder

The photographer has a direct view of the scene through the mirror and prism mechanism (pentaprism or pentamirror depending on the make and model).

Through the optical viewfinder we have the same point of view and the same frame that the final photo will have (approximately, since depending on the model the viewfinder sometimes does not cover 100% of the frame seen by the sensor)

For many photographers the optical viewfinder is essential, as it offers a very clean view of the scene, directly through the lens.

One of the advantages of the viewfinder (with respect to the rear LCD screen of a camera) is that it allows us to completely isolate ourselves from the environment and thus it is easier for us to focus our attention exclusively on the frame, without distractions.

Dedicated phase detection focusing system

It is a system with an independent sensor and a secondary mirror that depends on the main mirror.

It is only operational in photography, not in video. When we record video or use the rear screen in ‘Live View’ mode the mirror has to be raised all the time.

The phase detection system ( PDAF – Phase Detection AutoFocus ) is a very fast autofocus system.

Interchangeable lenses

The camera itself is the ‘body’ and the lens is mounted on that body.

The photographer can choose between different lenses the one that best suits the scene he wants to photograph.

Manual mode

Full control of different camera parameters: shutter speed, diaphragm aperture, ISO …

This is known as manual mode , which gives the photographer the possibility to freely choose how he wants to take each photograph.

In this type of camera, the design philosophy is based on offering the user full control. Unlike simple ‘ point and shoot ‘ compact cameras or mobile cameras , which are more intended to be used in automatic mode (the camera makes most of the decisions).

RAW format

All digital SLR cameras now have the ability to record photos in RAW format .

This format allows image information to be stored as it comes out of the sensor, without being processed by the camera and without loss of information due to compression, etc.

In addition, the RAW format stores the parameters with which the image was taken.

RAW format images are like film negative. They cannot be used directly for publishing, they must first be developed and then they can be exported to standard formats such as JPEG.

The main advantage of the RAW format is that it is the photographer who has control and can decide how to develop and process their image .

What is a professional camera?

Reflex cameras were sometimes referred to as ‘ professional cameras ‘, to distinguish them from other types of cameras, such as pocket compacts or superzoom (bridge) compact.

It was both a marketing strategy and an association of ideas: people saw professional photographers with that type of camera (large reflex cameras) and that association between professional (photographer) and reflex camera remained in the collective imagination.

But keep in mind that this name, professional camera, does not make much sense: cameras are not professional. Cameras are tools . They are sometimes used by professional photographers and other times by amateur photographers.

There are ranges, within the catalog of SLR cameras, that are more oriented to the professional sector and others that are more oriented to an amateur photographer.

This ‘professional range’ is designed to meet the needs of a photographer who makes a living taking photos or videos and depends on his team, and who has to work in many different circumstances, sometimes in very adverse situations.

Direct viewfinder cameras

In these cameras the viewfinder was located a few centimeters from the lens and aligned with it, but the point of view and the frame are different: the frame that the eye sees through the viewfinder is always the same, regardless of the lens that is using the camera. camera.

In cameras with a direct viewfinder, you could only guess the frame that the final image would have.

For example, if you placed a telephoto lens, you could only guess which part of the scene would appear in the photo. The viewfinder always offers the same angle of view, while the film picks up the angle of view provided by the lens.

Some viewfinders included reference lines for different focal lengths, for example the frame corresponding to a 50mm lens and a 75mm lens.

There was also the problem of parallax , as the photographer’s point of view was slightly offset from the lens’ axis of view.

And another additional problem is that with a direct optical viewfinder you do not have any information about the area of ​​the scene that will be in focus.

Rangefinder cameras

An evolution of the direct viewer was the rangefinder .

In the viewfinder of the rangefinder cameras, two images are combined: the main image that we would see with a direct viewfinder (the scene) and a second image that arrives through an auxiliary viewfinder physically separated by a few centimeters.

The auxiliary viewfinder typically included a mirror that is mechanically connected to the lens’s focusing system. Logically at that time there was no automatic focus, the focus was manual and was done by moving the focus ring of the lens.

Usually the auxiliary image only occupies a small portion in the center of the main viewer.

When the scene is out of focus we see the two images superimposed, not aligned. When the scene is in focus, the two images are combined perfectly aligned.

Some rangefinder cameras could also do a small parallax correction.

TLR (twin lens reflex) cameras

TLR (Twin Lens Reflex) cameras have a performance that would be halfway between rangefinders and reflex cameras that became popular later.

They use two identical lenses, with the same focal length, and share the same focusing mechanism.

One of the lenses sends its image directly to the film. Another lens sends the image to the viewfinder, usually through a mirror. The viewfinder on these cameras used to be at the top.

The main advantage is that the photographer sees the same frame that he will have in the final image, no matter what lens he is using (since the two are identical).

Another advantage is that manual focus is easier. The focusing mechanism works on both lenses at the same time and the image that appears in the viewfinder is large enough to see clearly if it is perfectly in focus. Screens or focus foils could also be used for more precision.


Film SLR cameras were a bit of the evolution of TLRs. They managed to do the same, but using a single lens and in a much smaller body. In English they are called SLR ( Single Lens Reflex) to distinguish them from the twin lens system.

EVIL / mirrorless / mirrorless cameras

EVIL cameras are the natural evolution of SLR cameras.

They are interchangeable lens cameras and have practically the same characteristics as SLR cameras. The only significant difference is that they do not use an optical viewfinder (they do not therefore need a moving mirror, pentaprism and all the internal mechanical part used by SLRs)

In mirrorless cameras it is the sensor that sends the image to the electronic viewfinder and / or the rear LCD screen.

Therefore, when it comes to framing, what we see through the viewfinder or screen is exactly the same as what we will see in the final image .

In addition, these cameras can perfectly simulate how the final image will be in terms of exposure, colors, etc.

Today it is very difficult to talk about the advantages and disadvantages of mirrorless cameras with respect to SLRs, rather it is about comparing specific models of both reflex and EVIL.

  • Some EVIL cameras are smaller and lighter than the typical SLR camera. But other models, especially in professional ranges, are very similar in size to SLRs.
  • Mirrorless cameras have fewer moving parts (the whole mirror mechanism that has to go up and down with every shot)
  • Some photographers prefer the optical viewfinders of the SLR because they give a clearer, more ‘natural’ vision, although the electronic viewfinders of the EVIL are today very good and offer much more information of the scene
  • EVIL cameras usually have a higher battery consumption: the electronic viewfinder and the sensor are working all the time when the camera is active, while in the SLR (when we use the optical viewfinder) the sensor only works at the time of taking the Photo.

Compact cameras

Compact cameras are those that do not allow lens exchange . They are manufactured with a certain optics, which is what the camera always operates with.

They also do not include an optical viewfinder (reflex). They therefore do not have a movable mirror. Some include an electronic viewfinder, others just the rear LCD screen.

In the compact camera category there is a huge range of features and performance.

There are very good mid-range compact cameras , with a very small and light format, high-quality optics and many of the functions that reflex cameras include (for example the possibility of working in manual mode, the possibility of recording in RAW format … )

You can also find high-end compact cameras , with features very similar to larger cameras, but in a small and lightweight format perfect for travel or to carry the camera in your pocket.

The compact high – end usually include a much bigger sensor, 1 inch or higher, which makes that provide very good image quality, especially in light situations where small sensor compact would begin to show its limitations.

Finally, the so-called highend or compact superzoom ‘bridge’ cameras .

These cameras have a format similar to SLRs in terms of size and weight. The optics are designed for each model and cannot be interchanged. They typically include lenses with a very wide zoom range ranging from wide frames (wide angle) to extreme telephoto (long range)

They are widely used cameras for photography of birds and nature (wild animals).

They are also a good option for travel photography because the focal range of the lens covers practically all situations.

They are usually cameras with a small sensor, therefore they have certain limitations in less light situations.