Advances in optics and image sensors for interchangeable-lens cameras have made choosing the right camera more complicated than just big vs. small.

Purchasing a new camera presents a wide array of choices in body style, optical range, display size, resolution and more. But until a few years ago, the first decision was a simple one: Did you want a compact camera with a single built-in lens, or did you want to pay a lot more money for a much larger camera that could work with multiple lenses?

Nowadays, even that choice is a complicated one. Compact cameras, for example, have a range of optics, from fixed-focal-length lenses to exceptionally long zooms — up to 36x. But the real change is in interchangeable-lens cameras, or ILCs.

Notice I wrote "ILC," not "SLR." That abbreviation stands for "single lens reflex." While most interchangeable-lens cameras sold today are still SLRs, that is no longer exclusively the case.

SLRs today work much as they did in the decades ruled by film photography. Pocket cameras and rangefinders had one path of light from lens to film and another for the viewfinder through which the user framed the shot. The SLR, on the other hand, had a single light path, with a mirror bouncing light from the lens to the optical viewfinder — a mirror that had to bounce out of the way for the camera to expose the film. The primary advantage of the SLR design was that the photographer saw through the optical viewfinder exactly what would be captured on film.

Digital photography meant the film was replaced with an electronic sensor that could feed an LCD with a real-time preview, which, in many ways, eliminated the need for an optical viewfinder. This is why optical viewfinders are now in short supply on compact cameras; manufacturers found that most casual photographers preferred the large display rather than the small see-through viewfinder.

For many years, however, the SLRs preferred by professionals and enthusiasts had larger, slower sensors that could not feed the LCD quickly enough to be a useful preview. To work around this issue, some manufacturers tried an additional sensor that powered only the display.

In recent years, the sensors have literally come up to speed. The large, high-resolution sensors are not only fast enough to provide a real-time preview on an LCD screen, they have proved fast enough for 30-frame-per-second, high-definition video. Professional filmmakers and videographers have turned to Canon and Nikon SLRs, thanks to their much smaller size and lower cost as compared to high-end film equipment. Canon, for example, promotes the fact that its SLRs were used for the TV show "House" and the movie "Captain America."

But if the large professional cameras could now feed their displays directly from the sensor, why still have an SLR moving mirror design? Was a true optical viewfinder — which still required the mirror configuration — that important to any but the most exacting professional photographers?

Enter the ILC

That's the question first answered by Olympus and Panasonic with their "Micro Four Thirds" cameras — and the answer was a resounding "no." Both companies produced bodies that, because they did not have to house the old-style mirror box, were more compact than SLRs. Despite the size reduction, these cameras had sensors that were almost eight times larger than those in pocket-size all-in-one cameras, and so yielded better image quality; and they had a mount for a variety of interchangeable lenses.

How small are ILCs? Panasonic's Lumix DMC-GF3 is comparable to a smartphone in size: 4.2 x 2.6 x 1.3 inches (a lens can add to that significantly). Sony and Samsung also offer ILCs that are small, compared to standard SLRs, but they have larger sensors than the Micro Four Thirds chip, giving them higher resolution and sensitivity. Micro Four Thirds sensors measure 17.3 x 13mm; the APS-C-size sensors used by Samsung and Sony measure 23.6 x 15.7mm.

Ever-improving technology means that resolution and sensitivity are less tightly linked to sensor size than they were just a few years ago. Even with the larger sensor, these alternative models are almost as compact as the Micro Four Thirds cameras: Sony's latest measures 4.3 x 2.4 x 1.3 inches.

What to choose

Where does that leave the potential new camera buyer? On the next page, I've provided a chart listing some of the latest ILC models and basic features. Both Canon and Nikon now offer very affordable SLRs that also capture HD video and come with articulating LCD displays. On the higher end, they offer greater resolution and sensitivity for unbeatable image quality in the below-$10,000 range, but neither company is offering anything much different from the HD video capture and real-time live displays released years ago.

While these two market leaders still command the vast majority of ILC sales, they have been slow to address the desires of those who want to continue using their wide collection of lenses, but who no longer wish to lug around a large, moving-mirror camera body. (Editor's note: At presstime, Nikon released its mirrorless Nikon 1 system.Visit photomediaonline.com for details.)

For those moving up from pocket-size cameras who want greater image quality and the creative ILC options without having to adjust to a large camera body, Panasonic and Olympus each offer aptly named "compact system cameras" that deliver much of the power and flexibility found in an SLR. If image quality size is a more important criterion than size, then it might be worth considering the options from Samsung and Sony, with their larger APS-C-size sensors.

And just to confuse things: Sony has yet another ILC design. This one is much like a standard SLR in size and function, except that while the mirror does bounce light to the autofocus mechanism, it does not need to flip out of the way to expose the sensor to light because it is translucent.

If you are comparison shopping for a new ILC, keep in mind that low-cost compact cameras are better than ever. It would not be far-fetched to say that a $200 pocketable model today takes better pictures than a very large $2,000 SLR from 10 years ago. Unless you are a very exacting photographer or take pictures in very demanding situations, you are likely going to be very pleased with the output of any model from the top five manufacturers priced from $200 to $500.

That said, SLRs and ILCs aimed at pros and enthusiasts have also improved incredibly in the last decade. And with the ever-increasing number of lenses — telephoto, wide-angle, wide aperture and more — they offer ever greater creative potential.