Not long ago it was only professional photographers, and enthusiasts with very deep pockets, who could afford a full frame DSLR. But there are now more options on the market than ever before, and the price of entry to the full frame fun has come down considerably. That makes it a good time for Gizmag to take a closer look at how the various models compare.

Here's our look at how five of the most popular enthusiast to professional full frame DSLRs stack up against each other. The selected cameras are:

Nit-pickers will be tempted to point out that the Sony isn't a DSLR. Because it uses translucent mirror technology it's technically an SLT (Single-Lens Translucent) camera. But it seemed daft to exclude it on that basis, if it looks like a DSLR and quacks like a DSLR, it's good enough to be compared with them.

Obvious omissions from the line-up include the mighty duo of the Canon EOS-1D X and Nikon D4. The logic for not including this pair is that their buyers typically know exactly what sort of camera they're in the market for and won't be comparing with less professional models. The 1DX and D4 deserve a side-by-side comparison, but that's for another time.

Size and Weight

The cameras here are larger and heavier than the offerings in our entry and mid-range DSLR comparison, and indeed our mirrorless camera comparison. But the models aimed at enthusiasts, Canon 6D, Nikon D600 and Sony A99 are not too dissimilar from the larger APS-C sensored DSLRs. In fact, if you're used to shooting with something like a Nikon D7000, the Nikon D600 or Canon 6D will probably feel very familiar in your hands.

However, there's still quite a wide range of bulk and heft among these five full frame cameras. The Canon EOS 5D III and Nikon D800 are unquestionably bigger and heavier. Aimed more at professionals and weighing in at 950 g and 1,000 g (before you've even mounted a lens), you might not want to wear one of these around your neck everyday while on vacation ... if you do you're likely to come home several inches shorter.

Megapixel Count

The undisputed megapixel monster of the group is the Nikon D800, with its 36.3 megapixel sensor. This dwarfs the 20.2 to 24.3 megapixels the others offer. But it's up to you whether that's a good thing. Sure, the camera will capture extra detail, but the resulting files will be much bigger and you'll need extra computer processing power and storage space to deal with them.

Many people would argue that the 20.2 to 24.3 megapixel range of the other four cameras is currently the sweet-spot for a full frame sensor. Though in a few years 80 megapixel full frame sensors will probably be the norm, and this view will be regarded as naive as those people who said "no-one will ever need more than five megapixels."

It's also worth noting that the "e" variation of the Nikon D800 cancels the effect of the anti-aliasing filter for even sharper and more detailed images. Ditching the AA filter has become something of a trend in 2013, with the Sony RX1R, Nikon D7100 and Ricoh GR all following suit. However, it does make a camera more prone to suffering from moire.

Autofocus

When it comes to autofocus, the Canon 5D III and Nikon D800 really show their higher-end caliber over the other cameras. This time the Canon comes out on top. With an impressive 61 focus points (of which 41 are the better cross type) the 5D III has one of the best autofocus systems on the market and shares its numbers with the Canon EOS 1DX. The Nikon D800, with 51 focus point (15 cross type) isn't a million miles behind and both are more than capable of keeping up with all but the fastest moving action.

Of the remaining three cameras, the Nikon D600 boasts 39 focus points (9 cross type), while the Sony A99 has fewer overall focus points with 19, but more cross type ones with 11. The Sony also benefits from 102 assist phase-detection points when used with compatible lenses. The Canon 6D lags somewhat behind others as it has a total of 11 focus points and only its central one is a cross type.

FPS Burst Rate

The Sony A99 and Canon 5D III share the speed crown when it comes to burst rate continuous shooting. Both are capable of a respectable 6 fps in full resolution, but the Sony also has the option of shooting at a quicker 8 or even 10 fps in crop modes.

The Nikon D600 comes in next with a marginally slower 5.5 fps and then the Canon 6D with 4.5 fps. The veritable tortoise of the group is the Nikon D800 which, due to the large size of the images it produces, can only muster a burst of 4 fps. It is, however, capable of upping this to 6 fps if shooting in DX APS-C crop mode, with the added battery grip.

ISO Range

Using modern full frame sensors, all of these cameras should excel whether shooting in bright sunlight or in lower light situations. Quite simply, because they have bigger sensors they can receive that much more light. While the Sony and both Canons have an ISO range of 100-25,600, the Nikons top out at 6,400 (though this can be expanded to 25,600).

However, it's worth remembering that while it might sound good on paper to be able to dial your ISO up to 25,600 in low light, the resulting images are not going to be the best quality and will suffer from noise and poor colors. Once you get up to 6,400 you should expect photos to resemble camera-phone shots.

Viewfinder and LCD

While DSLRs use optical viewfinders to see what the lens sees, it's worth remembering that the Sony (because it's an SLT) uses an electronic viewfinder. However, this is not the horrendous thing it would have been a couple of years ago, EVF technology has really come on. This one packs an impressive 2,359,000 dots meaning it's very sharp to look at, and is capable of displaying other information that an optical viewfinder could not.

Of the optical viewfinders, only the Canon 6D fails to show 100 percent of the full frame view, falling just short at 97 percent. This means that the actual photographs taken will be slightly wider than what was seen in the viewfinder.

The Sony again stands out when it comes to the rear monitor. This time because it not only has the highest resolution with 1,228,800 dots, but because it is also fully articulated, meaning it can be positioned to make shooting in awkward situations more comfortable.

Canon 5D III and Nikon D800 have larger 3.2 inch LCDs (with 1040k and 921k dots respectively) while the Canon 6D and Nikon D600 have three inch screens, each with the same resolution as their bigger brethren.

Storage Media and File Types

All of the cameras being compared are able to shoot on SD cards, though there are differences in how many cards they can take, and what other formats they can use. Multiple slots are good as it enables instant backup, the ability to shoot stills to one and video to another, or various other combinations.

The Canon 6D is very much the poor relation of the group having just one SD card slot. The Nikon D600 and the Sony A99 can both take two SD cards, though one of the slots on the Sony also has the nifty trick of being able to take any old Memory Stick Pro Duo cards you have lying about. The Canon 5D III and Nikon D800 pair an SD card slot with one for CompactFlash.

All of the cameras are capable of shooting both JPEG and RAW, though there are some differences. For example, the Canons can shoot smaller RAW files (like sRAW) while the Nikons only produce full RAW images.

Construction

The weight difference we noted between the enthusiast orientated cameras and those that are more likely to end up on professional duty, can easily be explained when looking at their construction. While all the cameras feature the use of magnesium alloy to make them stronger and more durable than their entry-level counterparts, this is done to varying degrees.

The Canon 6D and Nikon D600 use a couple of alloy plates, making them stronger than a typical all-plastic DSLR, but without getting too heavy. The Sony also features magnesium alloy panels, but it's the Canon 5D III and Nikon D800 that feel really solid with their more complete magnesium alloy chassis.

Video Modes

All of the cameras are capable of shooting Full HD video, but while the others can only shoot 1080p at 30/35/24 fps, the Sony A99 can do 60/50 fps. At 720p the other cameras have caught up and can also shoot 60/50 fps.

Wi-Fi Options

The Canon 6D is the only camera in the line-up to boast built-in wireless functions which include Wi-Fi for image transfer and even remote shooting, along with GPS for geotagging images. The Nikon D600 can gain similar functionality though the use of the optional and not too expensive WU-1b Wireless Mobile Adapter. However, the wireless transmitters for the Canon 5D III and Nikon D800 are going to set you back almost as much as an additional mid-range DSLR camera. Designed for professionals who need to send images fast and reliably, they can transfer images over a much greater distance.

Kit Lens

Kit lenses can offer great value, when bought with a new camera they normally cost a fraction of what they would on their own. Unfortunately, manufacturers tend not to offer kit lenses with higher-end cameras, presumably because buyers are likely to have better quality lenses already. As such the Sony A99, Canon 6D and the Nikon D800 are generally sold body only.

However, the Canon 6D and the Nikon D600 are both available with kit lenses. The 6D comes with a Canon EF 24-105mm IS F4 while the D600 is frequently bundled with a Nikkor 24-85mm f/3.5-4.5G ED VR. Both lenses are respectable all-rounders, and when purchased with their respective cameras, are good deals.

The extra reach makes the Canon kit lens that a bit more versatile, and it also benefits from being a constant F4. It's also worth remembering that both kit lenses have image stabilization, so even if you have better and faster lenses, these could be very viable options for video shooting.

Lens Mount

This one is fairly straight forward, each of the cameras is designed to use its manufacturers standard DSLR mount. This means the Canons can work with EF lenses, the Nikons take F mount lenses and the Sony works with A mount glass.

It's worth remembering that if you currently have lenses designed for a crop sensor DSLR, they are unlikely to cover the larger full-frame sensor in these cameras. So you'll either have to think about upgrading them or shoot in a crop mode, but that's not really the point of getting a full frame camera is it?

Price

As will have undoubtedly become clear when comparing these cameras, they are not all aimed at the same market. The Canon 6D and Nikon D600, being the more affordable of the cameras here, are aimed at enthusiasts while the Canon 5D III and the Nikon D800 are targeted at professionals (and enthusiasts with deep pockets). The Sony falls somewhere between these two pairs.

As such, the prices reflect this. The Canon 6D and Nikon D600 are $2,000 and $2,100 body only, or $2,600 and $2,700 with their kit lenses. The Sony comes in at $2,800 for the body only, with the Nikon D800 sitting above it at $3,000. The Canon 5D III is the most expensive, costing $3,500.

Summing up...

There are more options than ever in the full frame DSLR market, making it a great (if confusing) time for would-be buyers. There's no one camera that is the best of the bunch, it's all about picking the one which best suits your needs. Do you need the wireless capabilities of the Canon 6D or the resolution of the Nikon D800? You should also never underestimate the issue of which one feels right in your hands. It's always worth spending a bit of time with a camera before making a purchase. They all feel a bit different and one shape, or even button layout, might just suit you more than another.

The chances are that if you're in the market for a full frame DSLR, you'll already have a DSLR. That will undoubtedly have an impact on what camera you go for as you've got time invested in learning the system and money invested in lenses and accessories. However, it's worth remembering that if your current DSLR has an APS-C sensor and your lenses are designed for that, you're probably going to want to change them too, so you don't have to feel locked-in to a brand in quite the same way you might have ordinarily.

Personally, I think there are two cameras here which are really quite compelling. At the enthusiast end the Nikon D600 is hard to beat, it has a better autofocus system than the Canon 6D and is considerably cheaper than the Sony A99. While on the professional side, the Canon EOS 5D III seems to be the better all-rounder (and that's coming from a D800 owner) .

But, ultimately, all of the cameras compared here are very capable and can turn out amazing image quality, the likes of which would have been impossible a couple of years ago. As such, choosing between them means looking at which one offers the combination of build, features and price that best suits you.