EOS R System questions answered: all about Canon's full-frame mirrorless range

The EOS R System, Canon's groundbreaking mirrorless camera system, opens up new creative possibilities for photographers and filmmakers. At its heart is the innovative RF Mount, enabling a range of pioneering new RF lenses, including the acclaimed RF 28-70mm F2L USM zoom and innovative RF 600mm F11 IS STM and RF 800mm F11 IS STM prime lenses.

The EOS R, Canon's first full-frame mirrorless camera, was revolutionary for photographers and filmmakers. This was joined by the Canon EOS RP, which puts the power of full-frame mirrorless into a small, lightweight body, ideal for amateur photographers who are ready to take their photography to the next level.

Newer additions to the Canon EOS R System range set new standards in full-frame mirrorless photography and filmmaking. The EOS R6 is a hybrid camera capable of capturing incredible images and 4K video in low light, while the EOS R5 combines 45MP high-resolution stills and future-proof 8K movie recording.

The flagship camera in the range, the Canon EOS R3, brought a host of innovations. These include a stacked, back-illuminated sensor that enables 30fps continuous shooting, an astonishing Eye Control AF system that sets or switches the AF point by detecting what you're looking at, and low-light AF sensitivity to -7.5EV.

As well as new cameras, the range of RF lenses continues to grow. These include the RF 5.2mm F2.8L Dual Fisheye, Canon's innovative dual lens for 180° VR capture, as well as the ultra-wide RF 14-35mm F4L IS USM zoom lens and the RF 100mm F2.8L Macro IS USM lens for macro photography. There are also new super telephoto lenses: the RF 400mm F2.8L IS USM and RF 600mm F4L IS USM.

So is one of the Canon EOS R System cameras right for you? Does the EOS R System offer better image quality than a DSLR? Can you use your existing lenses and accessories? We put 12 frequently asked questions to Canon Europe Senior Product Specialist Mike Burnhill.

1. What is a full-frame camera, and what advantages does full-frame offer?
2. What is a mirrorless camera, and what advantages does mirrorless offer?
3. When looking at the EOS R6's low-light performance, what does -6.5EV mean?
4. Does the EOS R System offer better image quality than a DSLR?
5. Should I buy an EOS R System camera or a DSLR?
6. Can I use my existing lenses, flashes and accessories with EOS R System cameras?
7. Are there limitations to shooting video?
8. What's the point of shooting 8K video with the EOS R5 when hardly anyone has an 8K TV?
9. Why are there different types of multi-function controller on different EOS R System models?
10. Why do some EOS R System cameras have two card slots and not others?
11. Why did Canon decide to introduce in-body image stabilisation in the EOS R5 and EOS R6?
12. What are the key differences between the cameras in the EOS R System range?

"Characteristically, full-frame cameras offer shallower depth of field and greater control over depth of field than cameras with APS-C or smaller sensors. Portrait photographers in particular love that, because it helps subjects stand out more clearly from appealingly-blurred backgrounds."

"When we talk about mirrorless in this context, we mean an interchangeable lens camera which doesn't use a single-lens reflex mechanism (mirror), but instead an electronic viewfinder (EVF). The biggest advantages come from the fact that eliminating the mirror removes certain restrictions in lens design.

"Because you have a mirror in a DSLR, which has to have room to flip up out of the way when you take a picture, you basically have to work around that mirror system when you design a lens. If you want to make a 21mm lens, the centre point of the lens should be 21mm from the sensor. But if you have a 40mm mirror in the way, the lens can't be 21mm away. Therefore you have to add extra elements to move all the optics forward, and more glass to alter the focus point, and lenses become much more complex pieces of engineering. If you eliminate the mirror, you've got potentially much simpler lens design, so you can concentrate on image quality instead of constantly having to fight around the design issues such as retrofocus.

"In fact, when Canon developed the EOS R System, we didn't start with the decision to build a mirrorless camera. We began by asking 'What's the future of lens design? Where do we want to go with lenses?' The impetus was 'reimagining optical excellence', which led to the internal codename Project R, and that's how it comes to be named EOS R."

"The key decision was the development of the RF Mount, which is at the heart of the EOS R System. It has a wide throat similar to the EF mount, and a shorter flange distance from the mount to the sensor, so we can create groundbreaking new lenses that work at the optimum distance from the sensor. This enables the creation of faster, brighter, higher-quality optics with future-proof performance. The RF Mount also has an innovative 12-pin connection that enables radically faster communication between the lens and the body but also offers expansion for the future. One result of this is that EOS R System cameras (with the exception of the EOS RP) have exceptionally fast AF for full-frame mirrorless, interchangeable lens cameras and extremely effective real-time Digital Lens Optimization.

"Another advantage of eliminating the mirror is that the camera body can be made smaller and lighter, which makes a big difference if you're carrying it around with you for a long time. Like for like, EOS R System bodies are lighter than their DSLR equivalents. For instance, the EOS R5 weighs 738g with battery and memory card, while the EOS 5D Mark IV is 890g. There are lighter cameras out there, of course, but with the EOS R System it wasn't our aim to make the lightest cameras possible. We took the decision to construct the EOS R, EOS R5 and EOS R3 bodies using robust magnesium alloy, with pro standard sealing for dust and water resistance, because reliability and durability are important to the photographers we designed those models for.

"There are a few technical advantages to a mirrorless design, such as eliminating the vibration caused by 'mirror slap', but that is likely to be a concern only in a few very specific circumstances. More generally, getting rid of the mechanical mirror means the EOS R System is capable of completely silent shooting, which means you can shoot more discreetly in all kinds of settings, from weddings to wildlife photography. Using an EVF also makes it possible to live-preview your image with your shooting settings applied, as well as to see what you're shooting in previously prohibitive low-light conditions."

"The Canon Dual Pixel CMOS AF technology used in EOS R System cameras provides high-performance focus tracking in still photos and movies. It results in fast, accurate autofocus even in the kind of low-light conditions it was previously too dark to focus in. In one-shot mode, with a Canon RF 50mm F1.2L USM lens, the AF is effective down to -6.5EV on the EOS R6, -6EV on the EOS R5 and EOS R, -5EV on the EOS RP and -7.5EV on the EOS R3.

"To give you an idea of how dark that is: imagine you're out in some remote area at night, where there are no street lights and the only light is a quarter-moon. That's about the same brightness as -6.5EV. The EOS R6 will focus in those conditions, as long as there's some contrast. No camera will focus with zero contrast – if you point it at a white wall, no matter how bright it is, it won't focus, because there's nothing to measure between."

"It partly depends how you measure 'better', but by most criteria the EOS R System sets a new standard in full-frame image quality. Thanks to the improvements in technology and the image sensor, the 24.1-megapixel EOS R3 is resolving a similar amount of detail to the 30.4-megapixel EOS 5D Mark IV. The original Dual Pixel CMOS AF sensor delivers a perfect balance of rich, sharp detail and incredibly reliable low-light performance, and because almost every pixel in the sensor (100% vertically and 88% horizontally) is used for both imaging and autofocus, it ensures outstanding sharpness right across the frame.

"The Dual Pixel CMOS AF II introduced in the EOS R5 and EOS R6 goes even wider, covering 100% of the sensor in Face+Tracking and Auto Selection modes. The DIGIC X processor in these cameras enables us to use deep-learning artificial intelligence that recognises and tracks people's faces and eyes. It can identify a person's head even if they're wearing a mask and a helmet. The system also works with members of the cat and dog families, as well as birds to some extent.

"The CMOS sensor in the EOS R6 is based on the one in our flagship DSLR, the Canon EOS-1D X Mark III. So you'll get a similar level of image quality from both cameras. If you need to capture even more detail, the EOS R5's 45-megapixel resolution gives you incredible clarity. Only the 50-megapixel EOS 5DS and EOS 5DS R offer more resolution, but you really can't see a difference in an image produced by either camera. The actual amount of information in the two frames is identical, because the way in which we process the signal from the EOS R5's sensor makes up for the slight difference in megapixels. On top of that, the EOS R5 features stunning, class-leading dynamic range and high ISO performance. For the EOS R3 we've developed a back-illuminated, stacked sensor that's faster and more sensitive than any previous sensor, and it's at the heart of what that camera is able to do."

"If you're a professional photographer, you might feel there are advantages to a traditional Canon DSLR: a range of proven bodies and lenses to choose from, with all the reliability and ruggedness of the EOS system and a traditional optical viewfinder, which some users prefer for the direct connection it gives you with the scene.

"That said, when the EOS R System was first launched, professional photographers started adding EOS R System cameras to their kitbags, often as a second camera. Now that they've seen the advantages of the outstanding RF lenses, the low-light performance, the totally silent shutter and the major leap forward in autofocusing and tracking systems, EOS R System cameras are usually the main camera in a professional's kitbag."

"Although it's revolutionary in many ways, the EOS R System builds on Canon's 30-year EOS heritage. We retained the name 'EOS' for a reason – the EOS R System cameras are still part of the EOS family, with the compatibility that includes. We recognise that many photographers and filmmakers will have a substantial investment in EF and EF-S lenses, and you can use these lenses on EOS R System cameras with absolutely no loss of quality or functionality, using a choice of EF-EOS R mount adapters.

"With the standard Mount Adapter EF-EOS R you can use your EF and EF-S lenses on EOS R cameras seamlessly. With EF-S lenses, which are designed for EOS DSLRs with the smaller APS-C sensor, you'll get cropped images that match the smaller image circle of EF-S optics.

"The Control Ring Mount Adapter EF-EOS R adds a lens control ring, which is easy to use without taking the camera from your eye. This offers tactile manual control over various settings, just as you get on the RF lenses – you can customise it to adjust aperture, shutter speed, ISO sensitivity or exposure compensation, as you prefer – so in this sense it gives you the potential to get even more out of your existing lenses.

"Alternatively, the Drop-In Filter Mount Adapter EF-EOS R adds the ability to use drop-in filters, removing the need to fit filters on the front of a lens, which is especially useful for wide-angles with a large front lens element. It's available with either a variable neutral density filter or a circular polarising filter."

"Whichever of these adapters you choose, your EF and EF-S lenses are fully compatible. There are technically a few that are not fully compatible – with the Canon 35-80mm Power Zoom lens, which was available in around 1990 for about a year, the lens will autofocus and exposure is all the same, but the power zoom won't work; and with Super telephoto lenses before 2010, the focus lock button does not work but everything else operates as expected.

"As for accessories, most EOS cameras have their own model-specific battery grip for extended shoots. The EOS R5 and EOS R6 are both compatible with Battery Grip BG-R10, which features a multi-controller joystick for selecting the AF point when the camera is held vertically. But all EOS R System cameras are part of the EOS family, so your Speedlites will all fit, and you can attach them to standard tripods and so on.

"That said, there is one thing to watch for when using the EOS R3, which features the new Multi-Function shoe, making it possible for accessories to be powered from the camera. The change in the shoe means the weather sealing of flash accessories such as the Speedlite EL-1 or Speedlite 600EX-RT is no longer effective. When maintaining dust and weather resistance is important to you, Canon recommends adding the Multi-Function Shoe Adapter AD-E1.

"The EOS R5 and EOS R6 also use a new higher-capacity LP-E6NH battery, which gives a battery life of approximately 490 shots on the EOS R5 and 510 shots on the EOS R6 (in LCD power-saving mode in both cases). This is backwards-compatible too, so it can be used in every camera that's powered by the LP-E6 lithium-ion type of battery since it was introduced in 2008, including the EOS R, the EOS 5D Mark IV and EOS 6D Mark II. You can also use older LP-E6 batteries in the EOS R, EOS R5 and EOS R6, although you will get slightly less power. The EOS R3 uses the LP-E19 battery (as used in the EOS-1D X Mark III), which gives approximately 860 shots when using the LCD power-saving mode."

"We think filmmakers will love the EOS R System just as much as stills photographers. All the cameras in the range offer stunning 4K video recording – with a breakthrough 8K in the EOS R5 – and there are a host of creative movie-making features. You can control focus with great accuracy thanks to manual focus peaking, face detection and eye-detection AF, and the Dual Pixel CMOS AF allows you to move your point of focus smoothly and precisely using the touchscreen for professional focus pull effects.

"Naturally, you're not going to get every feature and function you'll find on a professional Cinema EOS camera, but professional workflow features such as 10-bit output and Canon Log make the EOS R, EOS R5, EOS R6 and EOS R3 ideal for use as a B-camera on large-scale productions where you need a compact and flexible tool."

"Recording in 8K gives you more options when it comes to editing. You can shoot wide with 8K and then punch in with a tighter crop or pan or zoom and still retain a 4K resolution image, which is probably as high as most people need at this moment in time.

"If you only need Full HD output, you're effectively giving yourself the option of using a 16x zoom in the edit. Because you're zooming into 8K worth of data, you get this amazingly natural zoom without any of the negative effects you'd get from using such a long zoom lens. It looks as if you've used a super-high quality Cinema parfocal zoom lens, with no breathing, no change in magnification and no change in exposure. This is like the best quality zoom you've ever seen.

"You also have a 4K HQ mode on the EOS R5, which oversamples the video from 8K to give the most detailed 4K image possible. If you record natively in 4K then you're actually only recording 25% of the data in both the red and blue channels due to the Bayer filter array on the sensor. The missing data can cause moiré and introduce artefacts, as well as softening the image.

"With 8K, though, you get 4K worth of red data and 4K worth of blue data, and together that gives you a much higher quality 4K signal. It's theoretically the maximum 4K signal you can get, so therefore sharpness and colour are massively improved and noise is reduced. And it's all saved at the same file size as standard 4K.

"The ability to shoot in 8K also offers new possibilities, such as when shooting 180° VR content using the Canon RF 5.2mm F2.8L Dual Fisheye lens. Shooting in 8K with this lens allows you to create 4K footage for each eye, ensuring a high-detail and realistic VR experience."

"With the EOS R, designing a whole new camera gave us the opportunity to try different ideas, such as removing the AF joystick and including the multi-function touch bar. We wanted to try a new interface that could do a number of things rather than a single task. Although some people loved it, we learned that most users still liked the tactile sensation of the multi-controller (joystick), so we brought it back for the EOS R5 and EOS R6.

"A large proportion of EOS R5 and EOS R6 users are transitioning from their DSLR equivalents, where that controller is universally used. Having the same familiar ergonomic feel to the EOS R System cameras means users are comfortable with them from day one. Often, customers have journeyed through successive generations of cameras and they can pick up a new camera and instinctively know where things are going to be.

"At the same time, we were developing the smart controller on the EOS-1D X Mark III. With the EOS R3, because we have a slightly bigger body and because we had very positive feedback on the smart controller, we included it there.

"It's about offering the best usability we can for the features available. We try to balance the new features and functions with familiar EOS handling, menus and so on, so you don't need to grasp a whole new system and can get up and running as quickly as possible."

"We totally understand why professionals value dual card slots. The Canon EOS-1D Mark II was the first camera with dual card slots. We know some people find it important for backup, or a more flexible workflow, or simply a feeling of security just in case. But not every user needs everything you'd find in a top-of-the-line professional camera. When we design cameras, we tend to be looking at who the customer is for that product, and what they want. That's our starting point. So we'll put some features in and leave some features out, based on what we feel the customer requires, rather than trying to cram everything in.

"The EOS R and EOS RP had one card slot, as they were aimed mainly at enthusiast users, but recent models have two card slots. The EOS R6 has two SD Card (UHS-II) slots, while the EOS R5 and EOS R3 have one high-speed CFexpress card slot and one SD card slot that's universally compatible. Those two cameras have different card slots because the feedback we received from our professional users told us that's what they wanted. Part of the reason is availability: although CFexpress cards are fantastic and super-fast, they're not always easy to get hold of, whereas SD cards are readily available in supermarkets and petrol stations around the world."

"The two types of image stabilisation are more effective with different types of lenses. So, in-body IS is better for wide-angle work, and lens-based IS is better for telephoto work. But the magic trick is combining the two systems to give a better performance across a wider range of focal lengths. That's what we've done with the EOS R5, EOS R6 and EOS R3, because the in-body IS alone wouldn't have significantly improved the level of stabilisation already offered by an IS lens, but having them synchronise together allows us to boost the overall performance.

"We've designed the system to work in tandem with any stabilised RF or EF lens, but you get a noticeable improvement from the in-body system when using an RF lens thanks to the faster communication between the camera and lens. The degree of improvement depends on the lens. The RF 85mm F1.2L USM and the RF 28-70mm F2L USM have very big image circles, for example, which means the IS system has more room to move. Neither of these lenses has built-in IS, but you can get up to 8 stops of stabilisation when they're used on the EOS R5, EOS R3 or EOS R6.

"If you attach an RF lens with built-in IS to these cameras then you'll also get up to 8 stops of stabilisation, but because the body and the lens systems are working together, you will actually see more of an improvement in performance than indicated by the rating. We have to measure stabilisation according to the CIPA standard. But this is done on a machine, and it doesn't take into account the low-level vibrations that are generated when a person breathes or has a raised heart rate or gets arm ache. So in real-world use you're going see even more of an improvement in image quality, because our combined IS system is correcting for different types of vibration that may not be considered in the CIPA standard."

"The flagship camera in the EOS R System is the EOS R3, which is aimed mainly at news and sports photographers. It's primarily about fast shooting, with a burst rate of up to 30fps, and the rapid delivery of images for use online and in print. Its users aren't going to need images big enough to fill a billboard, so its 24 megapixel resolution gives a balance of image quality and file size. You can also shoot video at 6K RAW.

"The EOS R5 offers 45-megapixel resolution, 8K RAW video recording and a 20fps frame-rate. Along with the EOS R3 and EOS R6, it introduces our next-generation DIGIC X processor, which is three times more powerful than the processor in the EOS R. DIGIC X increases our processing capabilities exponentially. Not only does it allow us to do 8K processing, it enables us to use the deep-learning AF system – to process the data from the sensor and match it to an on-board database.

"DIGIC X allows us to introduce a host of little improvements through the camera too. You can record video to one card and stills to the other card, for example, and rename folders in-camera. It also enables greater customisation options. One that I find particularly useful is setting AF Selection on the RF lens control ring. I've narrowed down my AF points to two modes – single point and automatic tracking – and I can switch between the two just by clicking the ring.

"The new processor also gives additional in-camera image processing functions. The EOS R5's Dual Pixel Raw option now features Portrait Relighting, which allows you to replicate the effect of using a reflector, and Background Clarity, which selectively boosts the contrast of the background in an image without affecting the subject.

"The EOS R6 sits between the EOS R5 and the EOS R. Although it has a lower resolution than the EOS R, its advanced AF system and high sensitivity expandable up to ISO 102,400 make it an even better choice for low-light work. It can shoot at 12fps using the mechanical shutter or 20fps using the electronic shutter, and it's better specified for video than the EOS R, including the ability to record full-frame 4K at 60p. The EOS R6 also has a better viewfinder, dual card slots and a joystick, so there's a whole host of upgrades over the EOS R.

"The EOS RP is a smaller, lighter camera aimed at advanced amateurs looking to take a step up to the full-frame mirrorless EOS R System. It is the lightest full-frame camera Canon has produced, making it ideal for travel, landscape and portrait photography and videography, or indeed any kind of creativity on the go.

"For more details, read our EOS R5 vs EOS R6 comparison article, or see the product pages for the EOS R3, EOS R5, EOS R6, EOS R and EOS RP, which include complete specifications and model comparisons."