What is a DSLR Camera? A Beginner’s Guide


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DSLR stands for Digital Single Lens Reflex. Cameras that use SLR technology have been in the scene since 1884 with the introduction of the first production-level SLR camera. When digital imaging techniques advanced, camera manufacturers moved on to digital sensors from analog films. The SLR in analog cameras changed to DSLR to account for the digital camera. We will go through the components, working, and pros and cons of DSLR cameras.

Components of a DSLR Camera

DSLR cameras have been dominating the photography front since the late 20th century. Accelerating advancement in digital electronics provided a new path for digital photography. Keep in mind that the same digital technology led to the development of mirrorless cameras. Let’s take a look at the components of a DSLR camera.


Manufacturers experimented with camera sensors once the technology was flexible. This resulted in inexpensive DSLRs available in the market. A sensor is a crucial part of the camera. It transforms the light into something readable by the camera machine: digital signals. The size of the image sensor in DSLR varies among different camera models.

Image Processor

Processing is the next step after the sensor converts the incident light into a digital form. An Image processor reads the sensor data and then creates an image or video file. It also determines the capability of camera performance in terms of autofocus, readout speed, continuous shooting, etc. Note that this is a very simplified explanation of a very complex system.


Shutters are the part of the camera that controls the exposure of the sensor to light. A very descriptive explanation of the working of the shutter is available in our article on Shutter Speed. We would suggest that you go through it, but we will also give a brief explanation here as well.

Similar to mirrorless cameras, DSLR cameras have both mechanical and electronic shutters. Electronic shutters are used mainly for video recording. Electronic shutters tend to skew the final image due to the rolling shutter effect. You will see this when you are shooting fast-moving objects. Mechanical shutters have a lesser rolling shutter effect than electronic shutters. However, mechanical parts limit the continuous drive speed of a camera. Also, the mechanical moving parts are not durable, unlike the electronic shutter.

Viewfinder in a DSLR Camera

Viewfinder Structure

The figure above shows the cross-section of an SLR system. Unlike electronic viewfinder, an optical viewfinder has parts that we can see in front of a camera. Let’s list out the components of this structure on by one.

  • 1. Lens – Lens let us set the field of view for the image. We change the focal length of the lens to find the desired field of view.
  • 2. Reflex Mirror – It is placed in front of the camera sensor. It flips upwards when the shutter release button is pressed.
  • 3. Shutter
  • 4. Sensor
  • 5. Focusing Screen
  • 6. Condenser Lens
  • 7. Optical Pentaprism
  • 8. Eyepiece / Viewfinder

Viewfinder Workflow

Light reaches the sensor through the lens. A reflex mirror blocks the way in a DSLR camera. This mirror, fixed in 45 degrees, reflects the light falling into the mirror to a combination of the focusing screen, a condenser lens, and a pentaprism. This setup focuses the light to form a sharp image. The pentaprism then reflexes the image to the viewfinder, hence the name single-lens reflex. This way, the viewfinder will display a sharp image of the field of view. Since there are only optical systems int the path, SLR produces no lag between the actual action and what is projected to the viewfinder.

When the shutter-release button is pressed, the mirror flips upwards exposing the sensor. The synchronicity between the mirror and shutter is crucial for a DSLR camera. However, while shooting long exposure photos, many photographers lock the mirror before taking the photo to avoid any shake while clicking the button. Even though this is not prevalent in fast or slow shutter speeds, this tip might help you in long exposure photographs.

This is how a DSLR is different from mirrorless cameras. Mirrorless cameras don’t use the reflex mirror. Instead, they use an electronic viewfinder that relays live feed from the sensor. Hence, the sensor has to stay always on for the photographer to see the field of view.


The inclusion of mirror and pentaprism in DSLRs demand for a larger body than the compact mirrorless cameras. The larger body allows the camera to accommodate a larger battery than a compact mirrorless camera. However, a lack of mirror allowed the manufacturers to add a built-in image stabilization system in mirrorless cameras.


Unlike mirrorless cameras, DSLR cameras have an in-built phase-detect autofocus sensor. The reflex mirror in front of the lens is a partially reflecting surface. The backside of the mirror has a similar reflecting surface that project light to the AF sensor placed horizontally at the body base. A dedicated phase shift AF sensor calculates the phase difference between the arriving light and drives the focusing motor to produce a sharp image.

How does a DSLR camera work?

Now that we have explained the main components governing the DSLR system let’s read them together to understand how an image is captured. While looking at the architecture of a DSLR, it is evident that they are almost similar to that of a mirrorless camera. The photographer composes the image through the optical viewfinder or Live View monitor. DSLR acts like a mirrorless camera when LiveView is enabled because the mirror slides upwards and the sensor is exposed. When the photographer presses the release shutter button, the reflex mirror flips up, and the shutter is released to expose the sensor. Once the sensor generates digital data, the image processor translates the digital data into a viewable image or video. Further, storage cards store the image or video.

Advantages and Disadvantages of DSLR cameras

The combination of a reflex mirror and pentaprism adds up to the mechanical movement inside a camera body. This mechanical part limits the continuous drift speed of a DSLR. But things are changing rapidly as technology is progressing. Take Canon 1DX Mark III for example.

Since DSLRs have been around for decades there is a wide variety of lenses to choose from. Given that, mirrorless cameras are also getting more lens support than ever. It is important to keep in mind that the selection of a camera is all about what you need. SLRs are bulky and heavier than mirrorless cameras. If you are a traveler, the weight of the camera might matter to you. Keep in mind that DSLRs don’t offer silent shutters. Since mirrorless cameras have electronic shutters, they can shoot photos silently. This can help you make nice candid portraits, or help in bird photography.

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Adarsh R

A blend of a photographer, a movie lover, and now a writer.