What is a DSLR Camera?

If it seems like there’s more new photography technology than what you can keep up with, you are probably correct. However, don’t let that deter you from learning the industry standards and terms within it. One of those terms that you’ll likely come across is the digital single-lens reflex (DSLR) camera, which has been the leading type of camera for still photography throughout the past decade.

While we are likely nearing (or already at) the end of the DSLR’s reign, the DSLR will be relevant in photography for many years to come. This guide will help you understand what a DSLR camera is and how it compares to other types of cameras.

Table of Contents

What Does DSLR Mean?

“Digital single-lens reflex” isn’t exactly the easiest term to understand off the bat. However, it makes more sense when you break down each part.

Digital: This implies that the camera is not film-based and that images are captured digitally on an image sensor instead of using photographic light-sensitive film. The film-based counterpart (which came before the DSLR) was called a single-lens reflex, or SLR, camera.

Single-Lens: This term is somewhat self-explanatory, and it means that only one lens is used on the camera. The lens is used in taking and previewing the image. This is opposed to a twin-lens reflex camera, which essentially uses one lens to take the picture and one lens to view the scene before the picture is taken.

Reflex: This refers to the fact that the photographer can see exactly what scene will be captured using a DSLR camera. The mirror in a DSLR directs the light toward the optical viewfinder. Other types of cameras sometimes have different mechanisms, and they don’t always project the exact scene that will be captured.

DSLR cameras operate using a mirror angled at 45 degrees, which directs light up toward the optical viewfinder for the photographer to see. The light is not routed through a digital path, which is why you can see a scene through a DSLR’s viewfinder when it is powered off.

When the shutter button is pressed, the mirror is lifted up to reveal the camera’s sensor for an exposure. This changes the path of light from going up into the viewfinder to going straight into the sensor, which is why there is a brief blackout of the viewfinder when taking a picture. This also produces the satisfying, yet sometimes inconvenient shutter noise that is commonly associated with DSLR cameras.

A diagram illustrating how a DSLR camera works, with a view of the internal components. Image by Guru Camera and licensed under CC BY 2.0.

While the first commercially-available DSLR cameras became available in the 1980s and 1990s, film cameras dominated the professional field for at least a decade due to various factors such as price and speed. A similar transition has been happening between DSLR and mirrorless cameras in recent years, and many would argue that we’ve reached the point where mirrorless cameras are overall more desirable than DSLRs. There are still arguments for DSLRs, however, which will be addressed in this article.

DSLR Body Designs

DSLR cameras come in two major body styles. The most common style is based on the traditional SLR camera from the days of film photography — it is the prototypical shape that most people think of when they think of an interchangeable-lens camera.

The Canon 5D Mark IV and Nikon D850 are two popular models that feature the more common DSLR body design.

Flagship DSLRs designed for professionals, however, typically feature a larger square-shaped design that has a battery grip built into the camera. This additional grip allows photographers to comfortably hold the camera the same way whether shooting in portrait or landscape orientation.

The flagship Canon EOS 1D X Mark III and Nikon D6 are two DSLR cameras that feature a larger pro camera design with built-in battery grips.

There are also optional battery grip attachments for lower-end DSLRs that can provide the same form factor, ergonomics, and increased battery life.

The Canon EOS Digital Rebel XTi (AKA Canon 400D) with a battery grip attached. Photo by Torsten Bätge and licensed under CC BY-SA 3.0.

DSLR Sensor Sizes

While there has been a wide range of sensor sizes used in DSLR cameras over the years, the two most common image sensor formats have been full frame and APS-C.

Higher-end (and more expensive) DSLRs typically feature full-frame sensors, which are the exact same size as a frame of 35mm film.

APS-C (Advanced Photo System type-C) DSLRs, which are also known as crop sensor camera bodies, feature a smaller image sensor that’s typically 1.4-1.6 times smaller than full frame and based on the vertical frames recorded on 35mm film by Super 35mm motion picture cameras.

The Canon 5D Mark IV (left) is a full-frame DSLR with a larger sensor than the Canon 90D APS-C DSLR (right).

Sensor formats other than full frame have different crop factors that provide photographers with a reference for the equivalent focal length of lenses relative to 35mm full frame. The same focal length will have a narrower field of view when used on a smaller sensor.

Popular DSLR Models and Brands

Canon and Nikon have generally been regarded as the leaders of the DSLR market, and their respective Canon EF and Nikon F lens ecosystems feature thousands of lenses developed over the years that continue to be compatible with the latest cameras.

The flagship Canon EOS-1D X Mark III and Nikon D6 are used by many professional sports and wedding photographers due to their speed and accurate autofocus. Other cameras such as the Canon 5D Mark IV and Nikon D850 have higher-resolution sensors, but slower autofocus and drive systems.

The Canon Rebel line of DSLRs are designed for beginning photographers and are some of the cheapest, smallest, and lightest DSLRs on the market. Ultimately, the brand of camera that you use is up to you and there are different theories on how much you should worry about that.

Other companies that still produce DSLR cameras include Pentax, Leica, and Sigma.

Point-and-Shoot vs DSLR

DSLR cameras are commonly thought of as “professional” cameras, even though a good number of them are geared toward amateur photographers. They are still more expensive than most point-and-shoot cameras (also known as compact cameras), mainly due to their increase in quality and capabilities. The ability to change lenses adds another potential cost because most photographers using a DSLR will want more than one lens.

Here are a few key differences between point-and-shoot cameras and DSLR cameras.

  • Image quality. DSLR cameras generally have larger sensors, which produce a higher-quality image. The sensor will also perform better in low-light conditions.
  • Viewfinder. Most point-and-shoot cameras display a digitally-processed preview of a scene on the back of an LCD screen. This can be difficult to view in certain lighting conditions and isn’t always an exact representation of how the scene will be captured.
  • Autofocus. Although it depends on the camera, DSLRs typically have faster and more accurate autofocus than point-and-shoot cameras.
  • Interchangeable lenses. Most point-and-shoot lenses offer one lens that will provide digital or optical zoom. It’s hard to make one lens that will cover all desirable focal lengths, so point-and-shoot cameras are usually limited in their fields of view. In addition, digital zoom magnifies images and compromises quality. Think of DSLR cameras as separate entities from their lenses, and every focal length can produce the same size and quality of image (disregarding differences in lens sharpness/quality).
  • Customizable. DSLR cameras generally have more settings and options than point-and-shoot cameras. While each camera is different, DSLR cameras generally offer more settings and controls.
  • Price. Point-and-shoot cameras are still generally less expensive than DSLR cameras, although you will find more expensive point-and-shoot cameras and less expensive DSLR cameras.
  • Size. Because of their small size and retractable lenses, point-and-shoot cameras are generally smaller and more portable than DSLR cameras. They’re usually lighter, as well.
  • Convenience. The overall convenience of not wanting to worry about camera settings is a factor that many consider when choosing a point-and-shoot camera. It’s easy to grab a point-and-shoot, toss it in your bag, and have it in case you decide you want to snap a few photos. While it’s also not very hard to do that with a DSLR, it’s more convenient with a point-and-shoot.

Mirrorless vs DSLR

What if a camera existed that had DSLR-like quality (or better) without all of the bulk? Enter the mirrorless camera, the DSLR’s challenger for the title of being the industry standard. The mirrorless vs DSLR debate is now one that photographers must pay attention to. Mirrorless cameras operate just like their name implies – there is no mirror required to reflect light to an optical viewfinder. Instead, an electronic viewfinder (EVF) is used to display a digital projection of the image.

The design differences between DSLR and mirrorless cameras. Illustrations by Canon.

Most mirrorless cameras still allow for one lens to be attached and changed, and mirrorless sensor sizes are comparable to (or sometimes larger than) DSLR cameras. There are upsides and downsides to both types of cameras, and it’s important to understand the key differences.

DSLR Advantages vs Mirrorless

  • Battery life. DSLRs generally have the upper hand here, mainly because it takes less power to move a mirror in a DSLR camera than it does to display a digital projection of the image in a mirrorless camera. Mirrorless cameras are also striving to be smaller than DSLR cameras, which means that batteries with lower capacities are often used. Although additional batteries can be purchased for either type of camera, brand-name batteries can be upwards of $50 each.
  • Cost and selection. Demand for entry-level DSLRs drove companies to produce less-expensive DSLR models with fewer features than professional models. While entry-level mirrorless cameras exist and are getting better with time, DSLRs still have a wider selection.
  • Lenses. DSLR lens technology has been developed for over a decade, so it will take time before the mirrorless lens selection is at the same caliber. However, many companies including third-party lens manufacturers are working to make more mirrorless-compatible lenses.
  • General industry resources. Since DSLR cameras have been around and leading the photography industry for many years, there are tons of DSLR-related resources available. From repair experts to guides on how to modify DSLR cameras, the DSLR world still has more resources than the mirrorless world. However, the mirrorless world is constantly expanding.
  • Well-reviewed and tested. In the past decade, DSLRs have been tested and reviewed at a greater scale than mirrorless cameras, at least at the professional level. Mirrorless is catching up, but DSLRs still have an advantage in terms of the sheer number of users who photograph using DSLRs professionally.

DSLR Disadvantages vs Mirrorless

  • Size. Mirrorless cameras do not have to incorporate an entire mirror and mirror-movement mechanism. Additionally, the use of an electronic viewfinder means that the viewfinder can be more compact. This means that mirrorless cameras are generally smaller than DSLR cameras, although the lens size and model sizes vary.
  • Speed. It takes fewer physical movements to capture an image on a mirrorless camera because a mirror doesn’t have to be flipped up and down with a press of the shutter button. Mirrorless cameras generally have faster frame rates than DSLR cameras, with professional-level mirrorless cameras often shooting 20-30 frames per second at full resolution. High-end DSLRs can keep up, but with greater limitations in terms of speed, resolution, or buffer capacity.
  • Autofocus. The autofocus system in a mirrorless camera can exist on the sensor itself since there is no mirror obstructing the sensor. This means that autofocus systems are generally faster and they can be more accurate than DSLR autofocus systems. There are also greater numbers of autofocus points on mirrorless systems because focusing happens on the sensor itself rather than with a separate autofocus sensor.
  • Sound. In situations where a camera shutter would be distracting, mirrorless cameras have the advantage. Many DSLRs have a “silent mode,” but the shutter noise is still somewhat audible. Mirrorless cameras don’t have to move a mirror when the shutter button is pressed, so there is no (or a very quiet) sound. This could be useful in scenarios where video is being shot on another camera and the sound of the shutter would interrupt the audio.


Whether you’re just getting into photography or you’ve been in the industry for a while, it’s important to understand the tools of the trade. DSLR cameras have been the leading cameras in the still photography industry for at least the past decade, and they may continue to be relevant far into the future. Keep an eye on other types of cameras, because the DSLR likely won’t be the leader (or maybe already isn’t) for long, but DSLRs will continue to be great options for professional and amateur photographers alike.

Image credits: Header photo by Basile Morin and licensed under CC BY-SA 4.0