"I'd rather have a DSLR for the money" - I've heard these words one too many times when talking about mirrorless cameras with beginner photographers. DSLR cameras have been the staple of image quality for a very long time now, and a sort of natural companion to any professional shooter. Many beginner photographers asking for advice on which DSLR to buy, especially those coming from point-and-shoots, find it very difficult to understand how a camera barely bigger than a compact can be a match to a big, solid-looking DSLR. After-all, wedding photographers, photojournalists, sports, wildlife photographers - basically anyone who is serious about digital photography - all carry DSLRs (with the exception of select few that rely on medium format and other specialized cameras).

Sensor Size and Image Quality Correlation

Image quality heavily depends on physical sensor size, not the size and look of the camera itself. Most point-and-shoot cameras have millions of pixels crammed into a tiny sensor, which limits their use in low-light environments and brings most of the scene into focus. DSLRs, on the other hand, have big sensors, which ultimately means much better low-light performance and ability to isolate subjects (thanks to fast interchangeable lenses that can provide shallow depth of field). Most interchangeable lens mirrorless cameras have the same or slightly smaller sensors as their APS-C DSLR counterparts and are capable of equally good, and sometimes even better results. Today, you don't choose one over the other based on image quality (unless you want to go full-frame), but on what you are planning to photograph. For specific needs such as sports and wildlife photography, where autofocus speed, subject tracking ability and lack of viewfinder lag are extremely important, DSLR cameras are still the way to go. True, mirrorless cameras have not fully caught up with DSLRs yet, but it is just a matter of time (more on this below).

For all other situations, a mirrorless camera makes much more sense - it's smaller, lighter, easier to carry, has potentially smaller lenses and because of all these reasons, is much more likely to be with you wherever you go. Once you get past the I-have-a-DSLR-which-is-cool factor, don't you find these advantages tempting and worthy of consideration?

The Potential

Mirrorless systems have a lot of potential. The reason why DSLRs are so big even in their smallest incarnations is because they have a mirror and an optical viewfinder, as shown below:

In order for the mirror to fit between the sensor and the lens mount, there needs to be a longer flange focal distance (distance between mount and film/sensor plane). Optical viewfinder and long flange focal distance make the camera taller and broader. However, other components are relatively small. Even those powerful image processors don't take up much space - the same EXPEED 3 processor used on the Nikon D800 is used on the much more compact mirrorless Nikon 1 V1. What this means is that it is possible to make a tough, high-quality, speedy camera with a large sensor and sufficient buffer by throwing away large moving components and replacing them with compact electronics. Potentially, that's an almost pocket-friendly D4 for you right there. With smaller lenses, too, as demonstrated by older rangefinder cameras. I'm a wedding photographer - it's my passion as well as main source of income. And I can honestly say I would love such a small camera, as plenty of other professional photographers would, I am sure.

What's more important is seeing how mirrorless cameras are slowly taking advantage of the theoretical possibilities. To be fair, compact system cameras weren't always that interesting to working professionals. At first, all of them were targeted at point-and-shoot users wanting to upgrade. Cameras like the original Sony NEX-5 were an alternative to budget DSLRs. They tempted buyers who didn't want the bulk of an entry-level DSLR, but craved the same image quality. Now, however, we have cameras that target professionals, such as Sony NEX-7, Olympus OM-D E-M5 and Fujifilm X-Pro1. Many of them offer fast burst modes, great video

The Market

As I've already pointed out, mirrorless cameras are getting more serious each year. We've seen huge strides in AF performance, EVF designs and image quality. OM-D E-M5 has proven that small 4/3 sensors are indeed a very well thought-out compromise, something that wasn't entirely obvious with their DSLR lineup. Fujifilm's sensor technology has finally helped us see that improvements can be made not only with increased number of pixels, ISO and dynamic range performance, but also with innovative approach to the very design of the matrix (something Sigma was eager to do as well with its Foveon sensors). All these improvements made sure that the mirrorless cameras receive deserved attention from those new to photography, as well as from advanced users. They make the small cameras that much more attractive to professional photographers craving for smaller and lighter gear. All that's missing is a full-frame interchangeable lens mirrorless camera.

The only option for a truly compact full-frame camera with interchangeable lenses is Leica, and has been so ever since M9 came out back in 2009. They may have their reasons, but Leica is also preposterously expensive as a system and the expense part is what puts it out of reach for most photographers. While good for certain types of photography, digital Leica rangefinders rely on manual focus and don't work well with longer lenses. There are also no current zoom lenses except for the Tri-Elmar, which has three focal lengths for you to choose from and costs nearly $5K. In other words, Leica is a very specialized tool, the use of which is difficult to understand for many, let alone justify the purchase. But the concept of a compact full frame camera does seem to have caught the attention of other manufacturers, not to mention the potential buyers. We now have professional-targeted APS-C mirrorless cameras, such as NEX-7 and X-Pro1. We have a full-frame compact camera in the shape of Sony RX-1. A full-frame mirrorless will come sooner or later and will be of much interest to a large portion of professional photographers. By then, contrast and hybrid autofocus systems will probably catch up, if not surpass, DSLR speeds.

So... Could a Compact Camera System truly Replace a DSLR?

Yes and No. Nasim already expressed his opinion about the future of cropped-sensor cameras and why he believes that small sensor DSLRs will be replaced by mirrorless cameras pretty soon. The day when capable mirrorless APS-C cameras become cheaper than entry-level DSLRs, I strongly believe most people will start switching to the lighter mirrorless options. We already have budget options such as the Sony NEX-F3 on the market, but they lack viewfinders (adding which is either impossible on low-end models or too expensive) and they lack advanced functionality and customization options found on entry-level DSLRs. But it is clear that the mirrorless market is already competing with the lower-end DSLR market. Take a look at some of the Sony commercials that show photographers that have no idea how to use a DSLR:

DSLR GEAR NO IDEA

These commercials are specifically targeted to market the Sony NEX series cameras. Sony wants people to move away from large DSLRs to much smaller NEX-series cameras. I am sure we will see more manufacturers doing this in the future...

Without a doubt, mirrorless cameras have plenty of advantages over their larger siblings. They are smaller, lighter and potentially come with smaller and lighter lenses. They are also quieter and more discreet, which photojournalists and street shooters are surely going to appreciate. So I just do not see how APS-C DSLRs will be able to compete with mirrorless cameras in the future.

What about full-frame DSLRs? I agree with Nasim's projection that full-frame is here to stay for a long time. Partly because manufacturers have invested so much into them, partly because they are simply more suitable for certain applications. In five years, I would love to have a non-yet-existing full-frame X-Pro5 hanging around my neck on weddings with a fast prime lens mounted. But I know I'd probably still have a workhorse DSLR with me. It's that much more secure in my hand thanks to its size and weight - in some situations, it's actually an advantage. It's that bit more dependable, having been around for such a long time. Sports and wildlife photographers are also likely to appreciate the bigger cameras for their ergonomics when mounted with large lenses.

However, there is a possibility that full-frame DSLRs become very specialized tools in the future, similar to medium format cameras today. What if Nikon came out with a full-frame mirrorless camera with superb battery life and all the same features (and more) you get from the latest generation DSLRs? Considering the shorter flange distance, this means that Nikon would have to replace all of its full-frame lenses, which obviously sounds like a bad proposition for anyone that owns lenses. But with a small electronic adapter, similar to the Nikon FT-1, you could potentially use all current and old DSLR lenses on such a mirrorless full-frame camera.

Maybe, in time, mirrorless cameras will make us all dump our bulky DSLR systems. Technology is changing fast, so I believe that it is just a matter of time. A mechanical mirror that has to move up and down before and after every exposure is just another potential point of failure, so losing it and thus simplifying the camera is the way of the future. Sony has already gotten rid of the mirror with their translucent SLT cameras, but the mirror is still there and it eats up some of the incoming light. SLT just seems like an intermediary step for now, which I am sure Sony will eventually get rid of in the future.

And for those that want the bulk and the build of a pro DSLR, a full-frame mirrorless camera can be designed to be the same size as current DSLRs. Once the mirror is removed, the light will pass through directly onto the shutter and the sensor. Imagine what benefits that would bring to wildlife and wedding photographers - you no longer have the loud mirror slap that disturbs wildlife and people. The "Quiet" mode would be replaced with a noise-free electronic shutter!

Why Do We Care?

By no means do I want to bash DSLR cameras as photographic tools. Instead, I'd rather celebrate the choice we've been given with the new camera systems - lighter and smaller, yet in many cases, just as capable to keep up with our varying demands. I'm a photographer. I've been through quite a few weddings and other jobs. My most go-to gear is rather lightweight and easy to lug around. Usually I don't need more than a camera body, a few backup batteries, a flash for rare occasions when there's no way around poor light and a couple of fast primes. But the possibility of having even less weight on my shoulders when I work for 14-16 hours straight is, undeniably, very attractive. If a couple of years ago I'd only consider a DSLR as a second body, today I'd put a mirrorless camera in that place with full confidence.

What's important to realize is that compact system cameras are catching up with established DSLR systems rapidly. They're not only good enough for some day-to-day photography anymore - they are good enough for clients, even if those clients don't yet realize it. Give the market two or three more years, and you'll probably find such a camera in most pro's bags next to the big stuff. Lenses will come and performance will come. And if you're on a lookout for your first DSLR camera, you may want to give Sony NEX, Fujifilm X, Olympus, Panasonic and other mirrorless camera brands a closer look. Perhaps DSLR is what will suit you better. Or perhaps you'll be happier with a smaller, but just as capable camera you can actually take with you anywhere you go? You've got choices, which is great news for all of us.