Low-light photography with the EOS R System

There are many situations in which you'll have to shoot in low-light conditions. These include night sky and astro photography, photographing wildlife at night, and capturing light trails or creative light painting using long exposures. You might be photographing a cityscape at night or a sunset, or even shooting down a coal mine, where the whole aim is depicting the ambient conditions, so that using flash would be inappropriate. Many photographers love shooting during the so-called "golden hour" just before dawn and just after sunset, when everything is bathed in warm colours and soft, diffused lighting but the general light level is lower than in daytime.

However, despite the emotive power that night photography and low-light photography can have, they present significant challenges. By definition, photography entails capturing light, and the less light you have to work with, the more difficult it will be to resolve detail and a wide range of tones. Focusing becomes tricky when you can't see clearly, and autofocus won't help when the camera can't see clearly either. Using a slower shutter speed to let in more light increases the risk of blurring, and raising the camera's ISO or light sensitivity setting typically results in undesirable image noise.

Here we'll explore how advances in camera technologies and innovations in design are remedying these key issues in low-light and night photography, resulting in hugely improved low-light performance in Canon's EOS R System cameras.

When photographers use light meters to measure the brightness of a scene and then adjust their camera settings to match, the unit of measurement is the Exposure Value or EV. A higher number (such as +10 EV) indicates you're exposing for a brighter subject, while a lower EV means a darker scene. In real-world terms, EVs approximately correspond to the following typical scenarios: 

• Daylight (full sun, distinct shadows) = 15 EV
• Hazy sunlight, soft shadows = 14 EV
• Overcast, diffuse light (no shadows) = 12-13 EV
• Landscape just after sunset = 11 EV
• Floodlit sports stadium at night = 9 EV
• Bright street with lighting at night = 8 EV
• Typical home interior = 7 EV
• Christmas tree lights = 4-5 EV
• Distant view of lighted buildings = 2 EV
• Nighttime landscape lit by full moon = -4 EV
• Nighttime landscape lit by half moon = -5 EV

You'll notice that several different combinations of aperture and shutter speed all give the same EV. For example, at ISO100, 1/500 sec at f/1.4 matches an EV of 10, which is the typical brightness of an outdoor scene in the golden hour, but so does 1 sec at f/32. If you add ISO into the equation and change the setting to ISO400, then 1/60 sec at f/16 also gives you an EV of 10. This means there isn't just a single correct setting that will result in a well-exposed photo of a given scene. (This is the same principle your camera applies when you use Aperture Priority mode, for example, rather than fully manual mode: change the aperture, and the camera will automatically adjust the shutter speed to keep the exposure correct.)

This is useful because altering any of the exposure settings won't just affect the exposure, but will change the look of the image. For example, altering the aperture also affects the depth of field – so you can't always use a wider aperture (lower f-number) to let in more light, because this also narrows the depth of field, which won't be suitable if you want foreground-to-background sharpness in a landscape.

Accordingly, you may often prefer to use a slower shutter speed when shooting in low light. However, long exposures introduce the risk of blurring due to camera shake or subject movement. Fortunately, this is a key area where the advanced technologies in EOS R System cameras can help.

Even with your camera mounted on the sturdiest of tripods, the simple act of pressing the shutter button can cause movement that may blur the image, particularly over a longer exposure. That's why it can be a good idea to trigger the shutter remotely, either using a remote shutter release or the Canon Camera Connect app on your smartphone or tablet. In a DSLR, there is a risk of (minor, but perceptible) vibration caused by "mirror slap" when the reflex mirror flips up to expose the sensor, but mirrorless cameras such as the EOS R System range eliminate this entirely. More broadly, Canon's latest cameras and lenses incorporate a range of image stabilisation technologies designed to counteract and minimise camera shake, no matter what the cause.

• Optical image stabilisation in IS lenses utilises gyro sensors in the lens to detect movement and a group of "floating" elements within the lens that can move to compensate for this movement and keep the image static on the camera sensor.
• The groundbreaking EOS R utilises a system one step up from this, in which the camera's imaging sensor also detects any image shifts and feeds motion vector data back to the lens processor, which then fine-tunes the stabilisation in real time. This system can accurately detect and compensate for low-frequency (slow) blur that used to be hard to detect with gyroscopic sensors alone but can be particularly problematic in long exposures. This Dual Sensing IS technology is made possible by the increased speed and bandwidth of communication between camera and lens delivered by Canon's innovative RF lens mount.
• In cameras with In-Body Image Stabilisation (IBIS), introduced in the EOS R5 and EOS R6 in 2020, the sensor itself "floats" magnetically and can also move in order to offset any type of camera movement.

That said, you'll deactivate IS for long exposures at night or shooting on a tripod, and IS won't help anyway if you can't see clearly enough to focus properly in the first place. Fortunately, EOS R System cameras also incorporate cutting-edge autofocus systems effective at very low EVs.

Dual Pixel CMOS AF is a Canon-developed technology introduced in 2013 and now in its second iteration in the latest camera models. Each pixel on the Dual Pixel CMOS sensor has two independent photodiodes (the parts of the sensor that record light intensity or brightness). The camera's processor compares the signals from the two photodiodes and, if they match, it knows that this point of the image is in focus. If they don't, it looks at pairs of photodiodes across a group of pixels, and can calculate which direction the lens needs to be adjusted to achieve sharp focus, and exactly how much focus adjustment is required. This works even at very low light levels, because what matters is the relative signal strength across pairs of photodiodes rather than the absolute level.

What's more, other AF systems use only a limited number of dedicated individual pixels for phase-detect AF, whereas Dual Pixel CMOS AF uses every pixel on the imaging sensor, which means that the active AF area covers in effect the entire image frame. It also gives the camera a significant advantage for tracking a subject around the frame, because there are no gaps between the AF points. The system works in video as well as stills and has been a game-changer for filmmakers who need reliable focusing and subject tracking.

"Dual Pixel CMOS AF technology has pushed the level of AF possible in low light, with AF now capable of -6 EV and lower," Mike points out. "Face and eye tracking are possible around -1 EV, and the technology also enables AF with small apertures."

Canon EOS R System cameras can autofocus down to unprecedented low light levels:¹

• Canon EOS R10: -4 EV
• Canon EOS R7: -5 EV
• Canon EOS RP: -5 EV
• Canon EOS R: -6 EV
• Canon EOS R6: -6 EV
• Canon EOS R5: -6 EV
• Canon EOS R6 Mark II: -6.5 EV
• Canon EOS R3: -7.5 EV

However, Mike points out, "all AF systems need some level of contrast for the system to measure and focus on." AF cannot be effective if the light level is so low that it cannot detect contrast, or if there is too little contrast in the scene to detect. When shooting in low light, you sometimes need to increase the ISO.

What is ISO? ISO is a standard scale to measure the light-sensitivity of film or a digital camera sensor. The name comes from the International Organisation for Standardisation, which combined the older ASA and DIN standards for film into a single standard in the 1970s. Higher-ISO films contained more light-sensitive silver halide, typically in the form of larger grains, which is why you literally saw more grain in images produced from these kinds of film. In digital photography, increasing the ISO setting actually increases the gain or amplification of the electronic signal produced by photons striking the sensor.

Contrary to what you often hear, this does not in itself increase the amount of image noise, the digital equivalent of film grain. Rather, in low-light photography, because image information depends on light, there is inherently a poorer signal-to-noise ratio, and increasing the gain simply amplifies both the image information and the noise already there in the image. The noise thus becomes more prominent.

This is addressed in modern Canon cameras by ever-improving noise-reduction technologies. "Noise reduction capabilities in current Canon EOS and Cinema EOS cameras are more sophisticated than they've ever been," Mike says. These include built-in, automated High ISO Speed noise reduction algorithms. (These can actually be applied at all ISO settings, but the effects are more noticeable at high ISOs.)

"Each camera has chrominance and luminance patterns mapped out in the system," Mike explains. "These presets, based on the sensor specification and ISO settings, basically tell the camera that when a JPEG is shot at a certain ISO, a specific noise reduction value needs to be applied."

Other built-in technologies include Multi-Shot noise reduction, which removes random noise by comparing multiple images taken from the same position, and Long Exposure noise reduction, which uses a modern version of dark frame subtraction to map out the fixed-pattern noise generated during a long exposure.

Alongside such technologies, Canon also continues to develop high-gain sensors with better resolving power and improved signal-to-noise ratios, paired with ever more advanced DIGIC image processors. The stacked design of the back-illuminated sensor in the EOS R3, for example, combines two layers of circuitry on the rear of the chip, enabling it to gather more light and greatly reduce noise. It also allows more of the processor circuitry to be brought into the sensor itself. "Being able to move the A/D converters closer to the signal means that there's less chance of interference generating more noise, which means it produces cleaner images," Mike reveals.

In addition, the stacked sensor design increases the speed at which the sensor can transmit image data to the camera's DIGIC X processor, where, in extreme low light, its processing capabilities can support High ISO noise reduction.

The CMOS sensors used across the EOS R System range all deliver some significant advantages over the CCD chips of old. For a start, they are more efficient at collecting light, which means better high-ISO performance with lower noise. The photo receptors also have a greater saturation capacity, meaning they can capture a much wider dynamic range.

For their part, filmmakers also benefit from Canon's revolutionary Dual Gain Output (DGO) sensor technology in the EOS C300 Mark III and EOS C70 pro video cameras. In the DGO sensor, each pixel is read at two different amplification levels in real-time. The higher amplification signal will capture details within the shadows with reduced noise, while a lower amplification signal captures detail in the highlights. The two readouts are then combined into one, delivering a super-clean output with a huge 16+ stops of dynamic range. DGO technology doesn't consume any more power than a traditional sensor, yet makes it possible to capture clean HDR footage even in low-light conditions.

One further thing about sensors. "It's tempting to assume that more megapixels always means better pictures, but it isn't that simple when it comes to low-light photography," Mike says. If two cameras offer the same pixel count but one has a physically larger sensor than the other, then the camera with the larger sensor will produce higher-quality low-light images. This is because the individual pixels – or more strictly photosites – in the larger sensor will be physically larger than those on the smaller sensor. In the same way that a wider bucket will collect more rainwater than a narrow bucket, a larger photosite can capture more light, which is critical in low-light photography.

Conversely, if two cameras have the same sensor size, then the camera with the lower megapixel count will perform better in low light, other things being equal – if it has fewer pixels in the same area, this means each photosite is larger, so it collects more light, which means a better signal-to-noise ratio.

It's important to keep this in mind when looking at camera specs, says Mike. "For the EOS R6 Mark II we wanted to continue to make the camera suitable for shooting in the widest range of conditions possible, so we designed for an optimal balance of improved resolution and the same excellent low-light ability."

The EOS R System family of cameras have other benefits for low-light shooting. As mirrorless cameras, they use an electronic shutter, which helps prevent the low-level vibration that may be caused by the moving elements in a mechanical shutter.

Also, the high-quality electronic viewfinders (EVFs) in the EOS R System range offer some significant advantages for low-light photography. Because an EVF is illuminated, it can compensate for low light levels and make it much easier to see a dimly-lit scene, giving you a clear view of your subject where an optical viewfinder (OVF) leaves you straining to see in the dark. When you're shooting at night, such as in astrophotography, an OVF won't provide the same clarity that you'll find with an EVF. An electronic viewfinder also lets you utilise features such as focus peaking and focus assist zoom, which are not available on an OVF.

Another major advantage of an EVF over an OVF is that you get to see a live preview of the image you are about to shoot, with your selected Picture Style and other settings applied. With live preview, you can see right away whether you need to adjust your exposure before you take the shot.

What's more, the range of RF lenses brings further advantages. Some RF lenses feature a new Subwavelength Structure Coating and an Air Sphere Coating that help prevent ghosting and flare, which is often a risk when shooting strongly backlit images during sunrise or sunset.

All EOS R System cameras make use of lens correction and other data stored within each lens, enabling the camera to correct for each lens's optical flaws and shortcomings as the images are captured if you're shooting JPEGs or during RAW processing in-camera if you're shooting RAW. Canon's Digital Lens Optimizer (DLO) technology is able to correct a wide variety of lens aberrations in-camera, including the effects of diffraction when shooting long exposures at small apertures.

"Canon has mapped all lenses at different focus, aperture and zoom positions to discover the types of aberrations that occur," Mike explains. "So DLO can apply corrections for these aberrations, producing higher-resolution images than would normally be available. This works with both RF and EF lenses when you use them on EOS R System cameras."

In all these ways – from groundbreaking image stabilisation and autofocus capabilities to advanced noise reduction, sensor and processor technologies – Canon EOS R System cameras and RF lenses continue to tackle the fundamental challenges of low-light photography and deliver low-light performance that was almost unimaginable in the past.

¹ Autofocus performance during still photo shooting, with an f/1.2 lens, Centre AF point, One-Shot AF, at 23°C/73°F, ISO100. Excluding RF lenses with Defocus Smoothing coating.