SLRs have been the dominant style of camera for almost 70 years. Over that time, SLRs have taken many forms and gone through many changes. What unites them all? What makes an SLR an SLR, and why have they become the most popular type of camera?
We’re here to answer all of these questions and more with an overview of SLR cameras in general. Keep scrolling for the text version.
What is an SLR?
SLR stands for Single Lens Reflex. What does that mean? Well, single lens means that there is only one lens, in contrast to TLR cameras that had separate lenses for viewing and taking. SLRs use one lens for both purposes, using a mechanical mirror and prism to bounce light into the viewfinder. That’s where the reflex comes from.
In this context, reflex means that the light is bouncing off of at least one mirror before reaching the photographer’s eye.
“Great,” you may think, “but if there’s a mirror bouncing the light into my eye then how does the photo end up on the film/sensor?”, which is a great question. Let's discuss
In most situations, the mirror will move up and out of the way when the shutter is pressed. In certain situations, the mirror may move sideways or not move at all, but the vast majority of SLRs have mirrors that move upwards.
This mechanism adds size, complexity, weight, and motion, but has a number of advantages that made it succeed over its competition.
History
In the 50s and earlier, rangefinder cameras were king. They offered the first accurate focusing aids, and companies like Leica and Contax produced excellent cameras with even better lenses.
It was Ihagee, though, that can claim the first true SLR. While Soviet engineers had laid out the groundwork for a commercial SLR, the Germans were the first to bring a product to market. The Kine Exakta had a moving mirror and used 35mm film in 1936, and their Exakta line of SLRs proved to be the first widely popular SLR series. The cameras were especially popular with the medical and scientific community, who preferred the greater flexibility of the SLR platform versus a rangefinder.
Other manufacturers were quick to take notice of the benefits of SLRs, including rangefinder giant Contax. Their first SLR, the Contax S, released in 1949 and was one of the first SLRs to include a pentaprism. This allowed for an eye-level finder rather than a waist-level one, making focusing and framing generally easier.
Japanese companies began to take inspiration from their German competitors, and 1951 saw the Asahi Optical Company release their first SLR, the Asahiflex I. Three years later they released the Asahiflex IIb, with an instant return mirror.
Before this, and after it as well for some, the mirror would remain up after the shutter was pressed. This meant that the viewfinder would be black until the shutter was cocked again.
Soon, Asahi would release their first SLR with a pentaprism, the Pentax. Get it? Pent-ax and pent-aprism? Soon other manufacturers, like Yashica, Minolta, and Miranda, would have SLRs of their own.
Then came the Nikon F. In April 1959, this SLR became the first successful “system” camera, with a large lineup of lenses and accessories aimed at professional photographers. Never before had there been a worthy competitor to professional rangefinders. It truly changed everything.
The next big development was through the lens (TTL) metering, introduced in 1961’s Pentax Spotmatic. Other manufacturers soon followed suit, attempting to one-up each other in automatic features throughout the 60s.
Konica was the first to introduce auto-exposure, with their AR mount allowing for shutter priority auto-exposure as early as 1965. From there, it was a race to see who could innovate the most. Brands either developed shutter or aperture priority auto-exposure, and marketed their SLRs based on the advantages of whichever system they chose.
1977’s Minolta XD-11 was the first SLR to be able to do both shutter and aperture-priority shooting, but Canon’s A-1 could do both at the same time one year later. This was the introduction of full-program exposure, where the camera would select both shutter speed and aperture for the photographer.
From here, focus was the only thing left to be automated. It took until 1985 for Minolta to introduce a lens mount built for autofocus with their Dynax // Maxxum // Alpha 7000. Two years later, Canon’s EF mount put autofocus on the map for even professional use, and started a dominance that continues to this day.
The Canon EOS-1v, a direct descendent of the original EOS-1, Canon's first professional camera for the EF mount.
The next big breakthrough in SLR design had nothing to do with the camera itself and more to do with how light was captured. While digital photography was invented by Kodak in 1975, it did not see widespread commercial use until the 1990s.
Digital photography led to a change in camera design as well, and now many SLRs have separate sensors for autofocus that are constantly receiving light. This makes focusing quite a bit faster. The arrival of digital technology turned the entire photographic industry on its head, but SLRs remained the prevalent camera design.
The important thing to remember, though, is that the basic principle of an SLR has not changed throughout the decades of rapid technological advancement.
Types of SLR
The concept of the single lens reflex system can be applied to many different types of cameras. It’s a bit more complicated than simply scaling the system up or down, but SLRs are feasible in every format, from the Pentax Auto 110 to large format Speed Graphic SLRs.
The Pentax Auto 110 is arguably the smallest true SLR ever sold, using 110 film cassettes and weighing only 172 grams. It also has interchangeable lenses.
Some interesting examples in 35mm are half-frame SLRs like the Yashica Samurai or Olympus Pen F. These two cameras are extremely different, but both use a half-sized mirror and take twice as many photos per roll. The Olympus has a mirror that flips sideways, but uses the same mirror system as other SLRs.
Some medium format cameras like the Pentax 67 seem like scaled up versions of 35mm SLRs. Even square, modular cameras like the Hasselblad 500c , though, are technically SLRs. They follow the basic principle of light going through the lens, bouncing off a mirror, and reaching the photographer’s eye.
Advantages
The SLR mirror system provides a number of advantages when compared with other camera designs, like rangefinders or TLRs.
One of the biggest advantages is that the photographer is looking directly through the lens. With a rangefinder or TLR, there is a difference between what the photographer sees and what the lens sees. This issue gets more dramatic when the subject of the photo is closer to the camera. It can be mitigated in a number of ways, but is a non-issue with an SLR. What you see is what you get.
Seeing directly through the viewfinder also allows the photographer to focus and frame more precisely. Rangefinder focusing can be very difficult if the camera is out of its comfort zone. Anyone who has tried to focus a rangefinder lens at f1.2 will agree. SLRs have no comfort zone, and will perform just as well with any lens that will fit onto it.
This leads into another big advantage of the SLR, the ability to change lenses. While many rangefinder cameras can also do this, SLRs have easier access to a much wider variety of lenses.
Most rangefinder lenses fall within 28mm and 135mm because rangefinders only have a fixed magnification viewfinder. They also require specific framelines in their viewfinders for accurate framing. To use lenses outside of this zone, a rangefinder will need an external viewfinder or something like Leica’s Visoflex. With a true SLR, as long as the lens will mount, it can be used.
Compared to their modern competitors, mirrorless cameras, SLRs still have the edge in terms of sales and accessibility. SLRs benefit from having no lag between real life and the photographer’s eye. A mirrorless camera’s EVF can never truly be lag-free because the digital sensor has to process the information. Some people also just generally prefer seeing the actual world through their camera’s viewfinder rather than a digital readout.
Autofocus is generally superior on SLRs than mirrorless cameras as well. This is because of the way SLR autofocus sensors work. Mirrorless sensors search the entire scene for contrasting edges, which takes longer than the phase detection systems of DSLRs. This system detects different wavelengths of light.
Mirrorless cameras do not have space for a dedicated autofocus sensor and have to rely on contrast detection autofocus. The only way for them to speed up their focusing is with software-based AI solutions. Sony and Panasonic in particular are pushing the boundaries of what AI can do for advanced autofocus.
Another modern benefit is lens stabilisation. This feature was made popular mainly by Canon with their EF lenses . Using a stabilised lens allows a photographer to get usable shots at much slower shutter speeds than they could otherwise. Especially with longer lenses, the effect is noticeable even just looking through the viewfinder.
Arguably the biggest advantage is that SLRs are the most popular type of camera. There are simply more SLR bodies and lenses than rangefinders, TLRs, or any other type of camera. Normally, this means prices are lower and specific items can be found more easily.
Disadvantages
Of course, the SLR is not a perfect design, and may not be the best choice for all situations.
One disadvantage is viewfinder blackout. When the mirror of an SLR moves up and out of the way, it blocks the camera’s viewfinder. This causes the photographer to lose sight of the frame for a split second.
If you’re taking slightly longer exposures or trying to track motion, this can be difficult and distracting. Rangefinders and TLRs do not have this issue because the photographer isn’t looking directly through the lens.
A second issue with SLRs is the noise. Because there is more internal motion than other camera types, SLRs are generally louder than other types of camera. With every shot, the mirror slaps up against the inside of the body.
This only becomes an issue when discretion is key, at sensitive events like a funeral or a wedding. It can be hard to hide the sound of an SLR, and the noise may be distracting or annoying to those at the event.
Like Nico said in the video, the constant “click-click-click-click” in the background while politicians give speeches is the mirror slap of SLRs.
Hard to hide the noise when you're shooting with a Hasselblad 500 series, but why would you want to?
Mirror slap poses another problem as well, however small it actually may be. The idea is that the motion of the mirror is enough to shake the camera and affect the final image. While cameras like the Pentax 6x7 get a bad reputation online, the actual effect of this phenomenon is debatable.
This is neglible with most SLRs, but for longer exposures it may be necessary to lock up the mirror before firing the shutter. Many professional cameras in 35mm or 120 have the ability to lock the mirror up for this reason.
For shorter exposures, try to follow the rule of keeping your shutter speed to 1/(lens focal length). If you’re using a 100mm lens, your minimum shutter speed should be 1/100th of a second to avoid camera shake.
Especially compared with rangefinders or new mirrorless cameras, SLRs lose the size and weight battle quite handily. Unfortunately, the mirror needs a larger, heavier body both to fit it and to mitigate the effects of mirror slap.
While some may think the larger size is more ergonomic, individual needs vary. Size and weight are definitely worth considering when purchasing an SLR camera.
Conclusions
SLRs have existed for almost 90 years, and have dominated the industry since the Nikon F released in 1958. From humble beginnings as the preferred tool of medical professionals, SLRs eventually stole the entire market from rangefinders and TLRs. These cameras are now relegated to niche use cases and old-school aficionados.
Only recently have SLRs begun to cede some market share to mirrorless cameras. Fortunately for SLR shooters, they have some distinct advantages that will prevent them from ever truly disappearing.
The basic principle of the SLR has stood the test of time and defined what a camera is. Light going through a lens, off a mirror, and into the eye is the way most people experience photography.
These cameras are ubiquitous, and represent some of the best ideas the photographic industry has ever had. If you or someone you know is thinking of getting into photography, film or digital, an SLR is arguably the best choice. Hopefully this article has helped clarify why.
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