The pixel count may be very similar to its predecessor but, in fact, the EOS 5D Mk III has a brand new sensor. There is a small increase in the image size, from 21.1 to 22.1 megapixels - 5616 x 3744 versus 5760 x 3840 - but this is just a little too much for a change in the true crop and the de-Bayer process to account for. It's common to get two similar silicon sources producing images 20 or 30 pixels different in dimensions from two different camera makers. Getting 144 more pixels on the long dimension indicates it's a new design. So when Canon claims a new type of photodiode, gapless microlenses and improved on-chip noise reduction, you can be sure it is a ground-up rework, not a fix applied to the existing one.

As expected, the Mk III jumps from a comfortable ISO 6400 highest true ISO to a just usable 25,600 before departing from the ISO standard to add two stops of High expanded sensitivity (to 102,400) and one stop of attenuated (50). At the same time, with the aid of a DIGIC-5+ processor and some beefed up mechanicals, it achieves six frames per second stills shooting. This was one of the main issues with the Mk II; its sequence speed barely faster than 4fps when that kind of rate was becoming associated with more entry-level DSLR cameras. So by the time the Mk II had been on sale for two years, cameras at a third of its price were offering 8fps and faster.

Edinburgh Zoo's male giant panda Yang Guang can often only be photographed through glass in low light. The 5D MkIII achieved fur-sharp resolution at ISO 1000, with a stabilised 1/80th wide open at f/4 on the 70-200mm L lens. The in-camera JPEG (above) has the usual problems with pandas - the black fur and black eyes. The raw file (below) allowed local corrections to improve detail in shaded areas, make the right eye as visible as the left, and improve overall resolution compared to the JPEG. Reflections in the glass were also retouched out.

Images (c) David Kilpatrick.

Canon originally pitched the 5D as a high-resolution option for the enthusiast and so-called semi-professional market, not intending it to replace the 1D series (of heavy-duty, high-speed models for editorial sports and news) or 1Ds (high-resolution, full-frame cameras aimed at advertising and commercial shooters) range. But there was a change of tack when Canon eventually realised the cult-like devotion praised upon the 5D's filmic image quality, compounded by the runaway success of the Mk II in the pro arena, first of all for its HD 1080p video, which was an industry first, and secondly for its combination of size, weight, features and price.

The Mk III now takes high-end features from the new EOS 1DX at twice its price. The processor and a new 61-point compact autofocus array come straight from the 1DX, while the magnesium body resembles the 7D, which was derived from the solid construction of the two-figure APS-C series. In place of the lighter plastic-skinned design of the earlier 5D models, this body has tight weatherproof seams and feels far more solid in the hand. Some ergonomic improvements are also derived from changes first made in the 7D, giving faster fulltime access to video shooting without having to move control settings chosen for stills.

The optical prism viewfinder is increased from 98 percent view to 100 percent. The earlier 5D models had interchangeable screens, with a method for lighting up active AF points. The Mk III does not, because the screen is a complex LCD sandwich assembly used to display the many setups and response states of the AF array. The downside to this change is that the screen seems dimmer, to my eye, and the passive state of the AF markings is more obtrusive. You are looking through what is almost a grid pattern of small rectangles filling the central APS-C zone, and you can't make this go away. When AF groups are active, they become more visible, and when focus is achieved, multiple points will highlight themselves.

Autofocus

This AF system is a major advance on the mere nine points of the Mk II, or the 19 of the 7D, offering a bewildering performance curve, with parts of the array becoming active as the aperture is increased from f/5.6 to f/2.8. It appears to have been designed with an APS-C format in mind for future use. This is something we have already seen in the 7D, where points that would sit in the central patch of a full frame sensor spread across most of the field of view.

The AF is not just more complex and capable, it is also 1.5 stops more sensitive for low-light use, although the exposure metering unit remains limited to EV1, eight times less sensitive than the AF. Since the two work together, with evaluative metering linked to the entire AF array, the limit for optimum performance is probably this not EV -2.

Above, the full image area, below, a magnified crop. At ISO 1250 even without any noise reduction applied the image is highly detailed. Focus was a challenge with this moving subject, but by using the pinpoint accuracy of the selectable AF points confirmed in the viewfinder, was confirmed on the baby marmoset's face. Images (c) David Kilpatrick.

Anyone who has hired a Canon rather than lived with one will know that the AF setup, through menus, is critical to assuring correct performance. Get the preferences wrong, and sharp subjects can be elusive. Get them right, and the most demanding action will be tracked and captured. That's why many specialist hire counters will set up your camera for you when you collect it, and it's why they restore cameras to factory defaults on return. For the Mk III, Canon has devised a new menu system that uses clear plain English (and presumably, all other languages) to say exactly what you can set, and what effect this will have.

Instead of obscure custom function labelling only clarified by poring over the camera manual while creating your setups, you can just pick up the camera and each main focus setup choice is explained as you go through the list. The manual explains how variously orientated strips of AF sensor are activated in set patterns when available apertures are detected, which helps you understand why some AF points can or cannot be selected. It also shows why you are wasting a lot of what you pay for if you do not use f/2.8 lenses. I used a 24mm f/1.4 with a lightning fast and dead accurate response, and a 70-200mm f/4 IS L, which was disappointing in comparison.

Accessories

It's good to see a vertical grip that not only uses the standard Canon lith-ion cells, but can also take a bunch of AAs. That's a great backup for travel shoots, or anywhere you might be unable to recharge, or run out of fully charged cells. And you are likely to have a few batteries around if you add the new wireless-remote Speedlite system to the camera. This is not dedicated only to new models, as it can work with a shoe-mounted master flash, or a radio controller. That's right, it is RF (on the same lines as Pocket Wizard or Skyport, or Quantum's TTL-enabled system) not infrared.

The entry price is around £1000 for the Speedlite 600EX-RT and WT-ES-RT controller, increasing by around £700 for each flash head up to a maximum of 15 in five groups. If you have about £10,000 to invest in complex off-camera flash and want to light up a 100-yard radius from many positions, you now have a camera maker's system capable of requiring 62 fresh alkaline cells at a loading. The Mk III lacks a built-in flash and can't match the 7D ability to control groups of the existing Speedlite models without requiring a shoe-mounted flash or commander.

Though the Canon does not have innovations to match Nikon's use of Ethernet, it will accept a wifi transmitter and a GPS positional data unit. These are connected through the USB port, so you can't use both at once.

Shooting modes

Canon has responded to constant demands for extreme bracketing, and offers exposure compensation of ±5 EV (manual) and auto bracketing of ±3 EV (in either 1/3rd or ½ EV steps). Using the more powerful processor, in-camera HDR is added, with a choice of ±1, ±2 or ±3 EV three-shot assembly and auto alignment of pixel detail if you work handheld. There are also five HDR effects, from "Natural" to "Art Embossed", which you may not want to try on portraits. And you can now shoot from two to nine overlaid multiple exposures, with a layer-type blending control (Additive, Average, Bright and Dark), not unlike similarly named Photoshop settings.

In live view mode, the Mk III offers four possible formats with three crops - 4:3, 16:9 and square 1:1. Unlike Nikon's D4, which has a fairly dense LCD viewfinder screen to enable grey masked crop areas in viewfinder mode, these crops only apply in live view and can not be shown in the prism finder. Live view must also be used to access a silent shooting mode. This uses an electronic first curtain and only ends the exposure with a physical shutter closure. It's not a true silent mode, but it is quieter than Nikon's. The battery life imposes limits on live view use, dropping from 850 shots per 1800mAh charge for normal shooting to only 180 if you use the preview function.

Remote triggering with the RC-6 infrared hand control only works from the front of the camera (there's no rear or top sensor), and since it is a separate still photo "drive" setting, it cannot be used to start video recording. This also applies to wired cable release through the N3-type terminal.

Noise and speed

Most potential buyers of the Mk III will have a simple enough question - does the two-stop increase in maximum ISO translate to all settings being two stops better? Given that most users have been happy to use ISO 1600 regularly and 3200 occasionally, that could mean 6400 for clean images and 12,800 when the light demands. After comparing similar images shot in 2010 with the Mk II at ISO 2500, new ones taken with the Mk III at 6400, and a range of different shots over the range of speeds, I'd give the Mk III one stop of real advantage in the usual working range - 800 to 3200 - but two stops as you go to what was the limit of the Mk II's capability and then beyond. Where 3200 was fully usable with the older camera, 6400 is with the new one. It's a touch grainer, but the noise is luminance and can be removed easily. The Mk II has much coarser underlying colour noise issues. If Adobe Camera Raw is turned back to the state it was when the Mk II came out (the 2003 process), the gain is multiplied, because the first assessments of Mk II performance were made with poor raw conversions.

What is surprising is that the Mk III avoids colour noise, or tinting of shadow colour, up to 25,600. The noise present at this and 12,800 is crisp and visible, but luminance based. It is very easy to get a clean image. This is not the case with the Mk III [does he mean Mk II?], and comparing some EOS 7D files, the benefit of full frame is massive. The 7D at 3200 has already left any kind of comfort zone. The Mk III at 6400 yields midtone to highlight quality you would once have been glad to see at ISO 100.

In comparisons, Nikon's new 16-megapixel, full-frame sensor is yet another complete EV step ahead. This you could expect, compared to 22 megapixels. The appearance of raw conversions through Adobe Camera Raw is very similar, with crisp easily smoothed out luminance noise and hardly any obtrusive colour noise.

After using both these cameras, I have to wonder whether flash is redundant. I've never used portable flash much, only for industrial and PR work of a certain type. With a Mk III I would work by ambient light. The raw files have the robust qualities needed to pull almost anything from difficult conditions.

Body design

Most of the new model is based on a mixture of control changes from the original 5 series, the 7D and the higher end 1 series. It's familiar, and overall it falls to the hand well. There is one exception in the default button allocations, which I found difficult to use; it must have been designed on paper not in practice. The ISO setting button, which must be held in to activate the dialog and enable the change, is sited just millimetres behind the front grip control dial that does the changing. It's so close that using just the right hand is difficult; you end up with your forefinger on the button and your index finger crammed up against it trying to change the setting. It's easier to use a left hand finger to press the button.

5D MkIII rear layout - features borrowed from the original 5 series, additions from the 7D like the movie/live view control, and the same screen as the top end 1DX

There's also a "Rate" button on the left hand of the rear screen - this may be a popular function today, importing pre-judged images into Lightroom complete with 1 to 5 rating, but I don't find it useful. You have to spend far too much time viewing and zooming in on images to rate them. The depth-of-field preview, a chunky button placed opposite the lens release on the mount, can be reassigned other functions (like Sony's similarly placed preview button, but with more choices). I did not program it but I can see how useful this will be as it's very fast indeed to hit with a finger without losing your grip on the camera.

It's a bit disappointing to see that the rear LCD screen remains fixed when so many lesser Canon bodies have articulated screens with the best hinge design around (no hanging under the body, side position to face forward). The 7D suffers the same deficit compared to the 600D and 60D, and the new 5D is based on the 7D body shape. A virtual horizon feature for levelling the camera has been added.

The 5D MkIII has dual card slots, accepting UDMA-7 and SDHC/XC fast SD cards.

The Mk III has twin card slots, for Compactflash up to UDMA-7, and SDHC/XC. I was able to test it with 45MB/s and 95MB/s Sandisk cards, and neither have any problems keeping up with video or with 6fps raw shooting. It can shoot only 13 raw images in one full speed burst, seven raw+JPEG, or 22 maximum size and quality JPEGs. The cards can be allocated to record simultaneous backups, sequentially, or with file quality split between two. This can be useful when fitting an EyeFi SD card dedicated to small JPEGs only. The camera has EyeFi support.

Good points of design include the C1, C2 and C3 dial-set custom setting recall positions - great if you move from studio to outdoor shooting frequently; and the inclusion of a headphone jack for monitoring during video, not even present in the high-end 1DX. You can also change audio level and other settings silently during filming using the rear control pad's new soft-touch functions.

Lens correction

Finally, there's one killer feature in the Mk III. Micro AF correction is important if you want good phase detection autofocus without front or back focus on all your lenses. The Mk III is the first DSLR to offer separate correction for the wide and tele end of zooms. Canon still recommends you do a Micro AF correction based on your normal shooting conditions, subjects and distance. Even with a prime lens, typical adjustment for a portrait studio could be different from adjustment to shoot track sports.

It's the normal process, but you select the extremes of the zoom range in turn and enter your figure, using live view and its 10x magnification to check against test shots. The camera does the rest, interpolating the values for intermediate focal lengths. You can also set chromatic abberation, distortion and vignetting correction for Canon lenses. This is one innovation we can expect to see in future cameras from all makers.