A trait shared by mirrorless camera systems, regardless of if they are micro 4/3rds, APS-C, or full frame, is that the flange distance, or distance from the mount to the sensor, is short in comparison to film cameras and DSLRs. This allows for the adaptation of lenses from other systems, including legacy glass. Adapters for almost any systems can be found, and are often extremely inexpensive*.*Higher quality adapters are available that can cost hundreds of dollars, but add features. Inexpensive adapters simply allow you to mount the lens from one system to another.When adapting lenses to your camera there are several considerationsOptical quality- New lenses have superior optical formulas and coatings to reduce aberrations and provide sharpness that stands up to modern, high megapixel sensors. Optical quality of and performance on modern sensors will vary.Adapter size- Depending on the system that you are adapting lenses from, the adaptor will add size and weight to your system. Leica mount lenses (M & M39 screw mount will be smaller in size. R mount Leica lenses use a larger, more traditionally sized adapter).Aperture control- Legacy/vintage lenses often have an aperture control ring on the lens. This allows you to use a cheap “dumb” adaptor and still have control of aperture. When adapting lenses such as Canon EOS or Nikon G lenses special, more expensive, adapters must be purchased that provides aperture control through electron connections.Focusing- Vintage lenses, for the vast majority, were manual focus to begin with and the technologies built in to the modern mirrorless bodies such as focus peaking and magnification make manual focusing an enjoyable experience (granted manual focus may not be an appealing option if you enjoy photographing moving subjects). Lenses with autofocusing abilities paired with adaptors with electronic autofocusing capabilities will provide limited usefulness. However focusing systems within mirrorless cameras continue to improve as does the technology in the adapters. Autofocusing capabilities will only get better (as promised in the A7rII).Exif Data- As inexpensive adaptors contain no electronic connections, no Exif data will be embedded in the files (focal length and aperture, ISO and shutter speed will be recorded as they are controlled by the camera).Cost- The cost of vintage glass will vary greatly. Many lenses are available in good condition for very little money on sites such as eBay. As adapting vintage lenses continues to increase in popularity, the secondary market for these pieces of glass continues to raise prices. Certain lenses are now being marketed as “rare," "hard to find," or "one of a kind" and the prices reflect that. Also, lenses made by Leica and Zeiss tend to reflect their higher initial MSRPs.Specialty adaptorso   Speed boosters – Reduce the crop factor and increases the maximum apertureo   Built in iris control – Adapter effectively has built in aperture controlo   Helicoid adaptor – Allows you to reduce the minimum focus distance of the lensPersonal ExperienceI adapt a Leica M mount Voigtlander 75mm f/1.8 Heliar to a Fuji X-E2 and Sony A7II. This is a completely manual lens with no electronic connections, however it is a fairly modern lens and is still sold new. Leica M mount lenses fall into the rangefinder category and have short flange distances, making their adapters, as well as the lenses much more compact. Even though the lens is physically compact, it feels very dense weighing in at 15oz.The lens is sharp, especially so when stopped down slightly. It exhibits fairly strong color fringing wide open, but gets better upon stopping down. The minimum focusing distance on the lens is .7 meters as is standard with most M mount lenses (older m mount lenses generally had a 1 meter minimum focusing distance). I purchased the Voigtlander VM-E close focus adapter (helicod apdapter) to mount this lens to the Sony A7II. This shortens the minimum focusing distance, but by no means allows for macro capabilities. When mounting extension tubes to attempt for closer focusing this combo vignettes even with only 10mm of extension tube.*I have read several articles that discuss using wide angle M mount lenses on digital sensors results in softening of the corners and vignetting filled with color fringing, but have no personal experience.With both the Fuji X-E2 and the Sony A7II, I utilize the combination of focus peaking and magnification to achieve focus. I use focus peaking to get my focus close and then use magnification to ensure critical focus. I will warn against relying too heavily on focusing peaking since it shows the entire focus plan rather than critical focus. For my uses, I do not miss autofocus provided with the focus assist aids built into the mirrorless cameras that I am using it with.Closing ThoughtsAs someone who thoroughly enjoys experimenting with new gear, the experience of adapting lenses is a positive one. Having to manually focus helps me to slow down and think more about the photographic process. Adapting lenses is not a solution to all shooting situations or all photographers using mirrorless cameras, but it provides an opportunity for many to use great Scott Gabrielli July 4th, 2015