The mirrorless camera revolution, which began with Micro Four Thirds cameras from Olympus and Panasonic and has continued with the Sony NEX series, has been a boon for enthusiasts who want D-SLR-like image quality, speed, and interchangeable lenses in cameras with much smaller bodies. Sony's Alpha NEX-C3, for one, packs an image sensor that is the same size as a D-SLR into a body that isn’t much bigger than a point-and-shoot camera. But what if you’ve already invested in an SLR with accompanying lenses?

Whether you’re simply looking to use some of your old glass with a new mirrorless camera, or if you are looking to acquire some new-to-you glass from the last century, adding an adapter to your mirrorless digital camera can open up a new world of photographic possibilities.

Thanks to the way optics work, you can adapt an SLR lens to a mirrorless camera. A lens is designed to be placed a precise distance from the sensor plane. This ensures that it can focus properly through its proper range. Because mirrorless cameras are much slimmer than other systems, it’s simply a matter of adding the proper amount of distance and making sure the mount is correct. And a lens adapter can achieve this.

Shooting with old lenses can be a lot of fun, and give a distinct look and feel to your photographs. And, if you already have a closet full of lenses, can save you quite a bit of money. Regardless of the brand of old lenses you have in storage—Canon, Nikon, Olympus, Minolta, Leica, Pentax, or something else—there’s a good chance that you’ll be able to find a third-party adapter. I purchased an adapter to use my Leica M lenses on the Sony NEX-C3 on eBay for about $20, including shipping. You can also find them pretty easily on Amazon.com, and at specialty camera shops.

Searching through online listings for the correct adapter might seem like a daunting task, but with a little bit of research it should be fairly simple to choose the correct adapter. You’ll need to know with certainty which mount your lens uses. Canon, for example, used a few mounts over the years—FD for manual focus SLRs, M39 screw mount for rangefinders, and EOS for autofocus SLRs. If you’re unsure which mount your older lens uses, take a look at the text around its front element. The mount type will often be listed there. If that fails, try searching the Web for information. Camerapedia is an excellent resource for information on older cameras, and you may also find PDF scans of manuals for long-discontinued models scattered around the Internet.

Of course, you’ll lose any sort of autofocus capability when you use a lens adapter—even when using a lens that supports autofocus on its native system. Most mirrorless cameras allow you to zoom in on your frame for fine focus. Some, like the Olympus PEN E-P3, have an accessory port that allows you to add a high-resolution electronic viewfinder.

You’ll also want to consider the sensor size of your camera before pairing it with an older lens. The image sensors in mirrorless bodies are smaller than the 35mm frames of film that most older lenses were originally meant to cover. The 50mm lens that was practically glued to your Pentax K1000 in the darkroom days will give you a field of view like a 100mm lens when used on a Micro Four Thirds camera, or a 75mm lens on a Sony NEX body.

You also may find that SLR lenses are a bit front heavy when used on smaller bodies. Many photographers, who are put off by the high price of Leica’s digital cameras, use a mirrorless camera as a digital platform for rangefinder lenses. Rangefinders are traditionally smaller than SLRs, as they use a fixed viewfinder for image framing and a rather complicated mechanical mechanism to confirm focus. Optics used on these cameras tend to smaller and lighter than those designed for SLRs, and balance very well with mirrorless bodies.

Revitalizing an old lens that’s hiding out in the back of your closet can be rewarding. Using it on your new, mirrorless camera can save you money, and the sentimental among us may like the idea of capturing images through the same lens that recorded many of your favorite moments in years past.