Canon EOS 70D Hands-on Preview

Preview based on a pre-production Canon EOS 70D

During the early days of digital SLRs, Canon was pretty much the undisputed leader in CMOS image sensor technology. Almost every new EOS model came with an increase in resolution and high ISO range, and when the EOS 7D appeared in late 2009, the company had progressed from 3MP to 18MP, and ISO 1600 to ISO 12800, in just over nine years. But since then Canon's APS-C cameras have all sported variants on the same basic sensor design, to the extent that you could be forgiven for wondering what on earth their engineers were doing all day. Now we know.

The EOS 70D is a mid-range SLR for enthusiast photographers that from the outside looks like a sensible, indeed desirable upgrade to the EOS 60D. It borrows many of the best bits from Canon's existing SLRs, including the autofocus sensor from the EOS 7D, the fully articulated touchscreen from the EOS 700D (Rebel T5i), and built-in Wi-Fi from the EOS 6D. But on the inside it sports an entirely new sensor that is, potentially, revolutionary. It offers 20.2MP resolution, but uses a 'Dual Pixel CMOS AF' design in which every single pixel is split into two separately-readable photodiodes, facing left and right. This means that in principle they are all capable of phase detection autofocus in live view and movie mode.

On-chip phase detection is nothing new - we first saw it in the Fujifilm F300EXR back in 2010. Since then it's been adopted in one form or another by most manufacturers, with arguably its most successful implementation coming in Nikon's 1 System mirrorless models. But because until now it's used relatively few active pixels scattered sparsely across the sensor, it's had practical limitations, often only covering a restricted area of the frame and struggling once the light drops below outdoor daylight levels. Canon says that its Dual Pixel AF system, in contrast, works across an area 80% of the frame width and height, in light levels as low as 0 EV, and at apertures down to F11. This means it could well be the most capable live view autofocus system we've yet seen on any type of camera.

We'll look at the technology behind the EOS 70D's live view AF in more detail later, but let's not forget that it has to work as a conventional SLR too. To this end it uses the same 19-point AF sensor as the EOS 7D for viewfinder shooting, but with slightly simplified control options in firmware. It can rattle shots off at 7fps for up to 65 frames in JPEG or 16 in RAW, and its standard ISO range covers 100-12800, with ISO 25600 as an expanded option. Image processing is via the DIGIC 5+ processor first seen in the EOS 5D Mark III.

In terms of control layout the EOS 70D is a logical evolution of the EOS 60D, adopting many of Canon's intervening updates and improvements. So it offers a full set of external controls to operate most key functions, and Canon's well-designed Quick Control screen to cover pretty much everything else. It also adopts the superb touchscreen interface that debuted on the EOS 650D (Rebel T4i), which we've found to be more useful than you might at first think. The 70D also regains an array of features that disappeared between the EOS 50D and 60D, such as AF microadjustment.

Canon EOS 70D key features

• 20.2MP APS-C 'Dual Pixel CMOS AF' sensor
• DIGIC 5+ image processor
• ISO 100-12800 standard, 25600 expanded
• 7fps continuous shooting, burst depth 65 JPEG / 16 RAW
• 'Silent' shutter mode
• 1080p30 video recording, stereo sound via external mic
• 19-point AF system, all points cross-type, sensitive to -0.5 EV
• 63-zone iFCL metering system
• 98% viewfinder coverage, 0.95x magnification, switchable gridlines and electronic level display
• Fully-articulated touchscreen, 1040k dot 3" ClearView II LCD, 3:2 aspect ratio
• Single SD/SDHC/SDXC card slot
• Built-in Wi-Fi
• Single-axis electronic level
• Built-in flash works as off-camera remote flash controller
• AF microadjustment (can be set individually for up to 40 lenses, remembered by lens serial number)
• In-camera High Dynamic Range and Multiple Exposure modes (JPEG-only)
• 'Creative Filter' image processing styles, previewed in live view

Key specs compared

In the table below we see how some of the EOS 70D's key specs measure up against its more expensive big brother, the EOS 7D, and its main rival, the Nikon D7100. What's interesting here is just how close the 70D is to the 7D in terms of spec - in much the same way as Nikon's D7000 made the D300S look almost redundant, it's quite difficult to see why most Canon users would now choose the top-end APS-C model.

Size and design compared to the EOS 60D

The EOS 70D directly replaces the EOS 60D in Canon's range, and is very similar in terms of size and design. It's a bit smaller though, and has a sensibly-updated control layout. Here we take a more-detailed look at the two cameras side-by-side.

From the front the EOS 70D looks almost identical to the 60D. But it's slimmed down a bit, being fractionally narrower. Look a little closer and you can also see that the 60D's front-facing mono microphone has gone (replaced by stereo mics on the top plate).
The two cameras are pretty similar from the back too, with the 70D retaining the same basic layout. It gains Canon's improved live view/movie mode controller, and has a physical switch to lock the rear dial against accidental operation rather than a button. Other than that it uses all the same buttons, just not necessarily in the same order.
From the top, again the 70D is very much a sensible evolution. The mode dial is simplified and now rotates continuously rather than having hard end stops, and there's a new AF area expansion button next to the shutter release. But the rest of the controls are all essentially the same.

Kit options and pricing

The EOS 70D will be sold body-only for £1079 / $1199 / €1099, as a kit with the EF-S 18-55mm f/3.5-5.6 IS STM for £1199.99 / $1340 / €1249, or with the EF-S 18-135mm f/3.5-5.6 IS STM lens for £1399.99 $1549 / €1499. The BG-E14 battery grip will cost £229.99 / $270 / €215.

If you're new to digital photography you may wish to read the Digital Photography Glossary before diving into this article (it may help you understand some of the terms used).

Conclusion / Recommendation / Ratings are based on the opinion of the reviewer, you should read the ENTIRE review before coming to your own conclusions.

Technology explained

The EOS 70D's headline feature is undoubtedly its unique 'Dual Pixel CMOS AF' sensor. This offers 20.2MP resolution, but uses two photodiodes for every single pixel ('facing' left and right), so that they're all capable of on-chip phase detection. This in turn promises hugely improved autofocus in both live view and movie recording. For example Canon says the EOS 70D will be able to hold a face in focus when the subject is moving back and forwards relative to the camera, even when filming with a fast prime lens at large apertures.

To understand what this technology is, and why it's a big deal, it's perhaps best to start with looking at how phase detection autofocus works, and some of the limitations of existing systems.

How phase detection autofocus works

Put simply, phase detection autofocus works by looking at the images projected by the left and right sides of the lens separately. When the subject is out of focus, these are 'out of phase' and don't coincide on the sensor, giving a blurred image. When the lens is moved into correct focus the images coincide, giving a sharp photograph. The key point is that it's possible to determine from a single measurement precisely how to move the lens to achieve correct focus.

Back Focus	In Focus	Front Focus
In this simplified schematic, you can see what happens to the image cast by the light passing through the left (blue dotted line) and right (red dotted lines) sides of the lens. When in focus, the light from both sides of the lens converges to create a focused image. However, when not in focus, the images projected by two sides of the lens do not overlap (they are out of phase with one another). Of course this is a massively simplified diagram with a single, vertical straight line as the subject (and no inversion of the image as it passes through the lens). The point is that we can derive information about focus if we can separately view light coming from opposite sides of the lens.

			How does a phase detection sensor 'see'? And we don't need the whole image to do this. Think about a strip of pixels taken from the sensor in the previous diagram. If you could make one such strip that receives light only from the left hand side of the lens and another that 'looks' only to the right-hand side of the lens, then you have enough information to find focus. By comparing images from just these two strips it's possible to work out not only how far but also in which direction the lens needs to be moved to bring them into phase.
Back Focus	In Focus	Front Focus

This basic approach has been used by SLRs since autofocus first appeared in the mid-1980s. Some light is allowed to pass through the main mirror and redirected down to an autofocus sensor in the base of camera. This works when shooting with the optical viewfinder, but the moment the camera is switched to live view and the mirror flips up, the autofocus sensor no longer receives any light and so can't be used. One solution to this is Sony's 'SLT' design, which uses a fixed mirror that always feeds some light to the AF sensor. But these cameras can no longer use optical viewfinders, and have to use electronic ones instead - the isn't a bad thing per se, but not all photographers like them.

An alternative solution that's used by many current cameras (including Canon's recent entry-level SLRs, and many mirrorless cameras) is on-chip phase detection. Some of the pixels on the main image sensor are masked black on one half, so that they only register light coming from one side of the lens. By using left- and right-facing pixels, it's possible to implement phase detection focusing using the image sensor itself.

This diagram shows how on-chip phase detection was implemented on the first cameras to use it, the Fujifilm F300 EXR and Z800 EXR. Click here to read more about their PDAF system.

The problem with on-chip phase detection is that these pixels only register half the usual amount of light. So when it comes to taking the photograph they output a lower-quality noisier signal, and can't always be used for imaging, especially in low light; instead their values have to be interpolated from the surrounding pixels. This in turn means there can't be too many of them on the sensor, or image quality will drop noticeably. And as light levels drop, the signal quality from the masked pixels can deteriorate to the point that the focusing system doesn't work either. Canon's fix for all of these problems is, rather than masking the pixels, to split them into two.

Canon's new 'Dual Pixel CMOS AF' sensor

Canon's schematic of its Dual Pixel CMOS AF sensor structure. The top layer illustrates the light-gathering microlenses and conventional Bayer-type colour filter array. The lower layer shows how each pixel is split into two photodiodes, left and right, which are coloured blue and red respectively. (Note that this does not indicate different colour sensitivity.)

Canon's 'Dual Pixel CMOS AF' sensor looks at the concept of on-chip phase detection, and takes it to a logical conclusion. Instead of masking some pixels so they only 'face' left or right, it uses two photodiodes for each pixel, so every single one has a left- and right-facing component that can be used for phase detection. When a photograph is taken, the output from the two photodiodes is combined. The diagram below illustrates what this means for phase detection AF.

Lens back-focused Overall view	Lens back-focused Left-facing photosites	Lens back-focused Right-facing photosites
Lens in focus Overall view	Lens in focus Left-facing photosites	Lens in focus Right-facing photosites

This immediately brings many theoretical advantages. In principle there's no significant light loss overall, so the quality of the output pixels shouldn't be lower compared to a conventional sensor. But because there are many more pixels capable of phase detection on the sensor, they can be used together for more accurate focusing, and in principle the system should work much better in low light.

Because the phase detection sites are more closely-spaced, the system can also work at small apertures, which allows continuous focusing in movie mode with the lens stopped down, or functional autofocus when using long lenses with teleconverters. Last but not least, because the main image sensor is used for focusing, it should be effectively immune from any systematic front- or back-focus problems that can come from an AF sensor with a separate light path.

According the Canon the EOS 70D's Dual Pixel CMOS AF system has the following key characteristics:

• Usable phase detection AF area covers 80% of the frame horizontally and vertically
• AF works at apertures down to F11
• AF works in light levels as low as 0 EV
• Can work with face detection to keep moving subjects in focus

Caon says the EOS 70D's 'Dual Pixel Hybrid AF' is active across 80% or the frame by width and height, as outlined here. (Pixels towards the edge aren't used for AF for technical reasons, despite having the same dual-photodiode structure.) This means that almost wherever your subject is in the frame, the camera can attempt to track focus on it during live view and movie shooting using its on-sensor phase detection.

Lens compatibility

Canon has made no fewer than 156 EF lens models in the 26 years since the EOS system first appeared, and it says that 103 of them fully support Dual Pixel CMOS AF, including all current lenses. This means that these lenses only ever use phase detection for live view and movie focusing - there's no need for a slower contrast detection step. The other 53 lenses count as partially supported, which means that for One-Shot AF (either stills or movie) they use a hybrid system with phase detection to determine the initial focus movement, and contrast detection to fine-tune correct focus. The full list of lens compatibility is on Canon's website.

What we don't know anything about, as yet, is how well third party lenses will work.

But does it actually work?

This, of course, is the million-dollar question - technology can be as conceptually clever as you like, but ultimately all that matters is whether it works in the real world. So far we've only had our hands on a non-final EOS 70D for a relatively short time, but our initial impressions are pretty positive. With the EF-S 18-55mm f/3.5-5.6 IS STM kit zoom, the camera is clearly much faster and more decisive at focusing in Live View than any previous EOS - or indeed any other SLR. We'll need to test it with more lenses in real-world shooting, but at the moment we're cautiously optimistic.

The big unknown right now is image quality - the 70D uses a 20.2MP sensor but the image is formed from 40.3M photodiodes, which is a lot to fit onto an APS-C chip. We're assuming that much of the work Canon has been doing over the past few years has been directed towards keeping noise as low as possible, and the company is confident enough to offer the same ISO range as its latest 18MP APS-C cameras (100 - 12800, with 25600 as an extended option). But ultimately the proof can only come from the images themselves.

In the meantime, as part of its launch materials, Canon has produced some video content highlighting the abilities of the 70D's AF system. Click here to see the footage.

Canon EOS 70D specifications

Body & Design

The EOS 70D looks very much like the EOS 60D, although it's actually a little smaller. Body construction is mainly plastic, but in this case that's not much to worry about - it still feels nicely put together. All of the main shooting controls are in essentially the same places, but some of the secondary ones have been moved around or revamped. Overall there's not a lot of space left on the camera where more buttons could realistically have been placed.

Top of camera

The top of the 70D very closely resembles that of the EOS 60D. The buttons along the top of the LCD screen each serve a single purpose rather than doubling-up, giving direct access to autofocus and drive modes, metering and ISO (which is easily changed with the camera to your eye). The exposure mode dial has been simplified to group the various automated scene modes (portrait, landscape, sports etc) under a single position, and a pair of stereo microphones placed behind the pop-up flash housing replace the mono mic that was on the front of the 60D.

The small button between the shutter release and the front dial is a dedicated focus area expansion control. Pressing it allows you to expand the AF area from a single point to progressively larger groups of points - useful when tracking a moving subject.

Weather sealing

Canon's spec sheet for the EOS 70D says it has water and dust resistance 'equivalent to the EOS-1N' - Canon's professional 35mm SLR in the mid-1990s. It's debatable how much this information will mean to most buyers, but the implication is that it shouldn't be fazed by a splash of rain. The diagram below gives an idea of how the body is sealed (courtesy of Canon EU).

In your hand

The EOS 70D has a good-sized grip and sits solidly in your hand; anyone who's used a recent twin-dial Canon EOS should be able to pick it up and feel right at home. Most of the key controls are well-placed for operation with the camera to your eye, but if you want to move the focus point using the multi-controller, this requires a fairly large movement of your thumb downwards. You can also move the AF point with the front and rear dials, but have to press the AF point selection button first.

Articulating Touchscreen

The EOS 70D uses a fully articulated touchscreen that's very similar to that used in the EOS 650D and EOS 700D. This means it's substantially improved on the one in the EOS 60D, as the air gap between the cover glass and the screen itself has been eliminated; this should improve visibility in bright light.

The screen can flip out and rotate to point directly downwards, upwards or even forwards for shooting self-portraits (in this position the camera handily mirrors the live view display). It can also be folded up with the screen facing inwards to the camera for added protection (or if you somehow prefer an old-fashioned film-camera experience).

The screen is also touch-sensitive, and as on Canon's recent entry-level models, absolutely every aspect of the camera's interface can be controlled by touch. In concert with the camera's Q button, it means a wide range of settings can be changed quickly and intuitively. This doesn't make so much difference while shooting with the optical viewfinder, when you'll probably want to use conventional 'hard' controls as far as possible. But it's genuinely useful in live view or when shooting from a tripod, allowing the focus point to be selected (and, if you like, the shutter to be released) simply by touching the screen.

In movie mode you can also 'pull' focus to a new subject by tapping the touchscreen, with the camera shifting focus smoothly in a controlled fashion. We've seen this before on Canon's Hybrid AF cameras like the EOS 100D / Rebel SL1, but with the 70D's new AF system it promises to be a particularly neat trick.

The screen has a high-sensitivity setting which Canon says allows operation with (thin) gloves. Alternatively you can turn the touchscreen off altogether if you don't like it.

Viewfinder

The EOS 70D uses a glass pentaprism viewfinder with 98% coverage and 0.95x magnification. This is an improvement on the 96% coverage offered by the 60D, and places it much closer to competitors like the Nikon D7100 and Pentax K-5 II, which both offer 100% coverage and slightly higher effective magnification. Of course it still can't match full-frame cameras like the EOS 6D.

The 70D's viewfinder also gains a switchable gridline overlay, along with the neat trick of being able to use the AF array indicators to display a single-axis electronic level in the viewfinder to help keep your horizons straight (both features lifted from the EOS 7D).

Battery Grip BG-E14

The EOS 70D gets a new battery grip, the BG-E14.
The grip replicates the main control set for portrait format shooting, including the dedicated AF-area expansion button. The camera is designed so the rear dial is reasonably accessible when using the grip.	It will take either two LP-E6 batteries to double the camera's endurance, or six AA batteries (via a second tray included in the box). There's also a storage slot for the camera's battery compartment door.