Sony a7RIII mirror-less lens adapters

Question in ignorance: How in the world can an adapter (Canon lens to Sony) still focus at infinity given the adapter's added depth? (I place it in context of three ring lens-extenders used for macro work... infinity is no longer available.

EJ's eye-opening convincing choice of the Sony 7RIII is beyond sobering. After several decades of Canon-equipment professionally used, bodies and lenses... maybe it IS time to move on. In hindsight even corporate Kodak and Kodachrome film came to an end, the Yellow Box once a world-recognized standard.

Downside of adapters if I understand this correctly: the bevy of Canon lenses I have will work... but on a relative basis are bulky and heavy compared to Sigma Art Series or Sony's GM high-end equivalent lenses.

Reading EJ's highly informative lists of "Best Lens" recommendations the Sony and Sigma names appear with stark frequency. (A few years previous I bought the Sigma 35mm f/2.8 Art Series and their computer focus tuning system - it was a eye-opening, even today remains my benchmark of quality, resolution, color, and smoothness of lens-ring focus.)

Logic suggests buy the Sony body and lenses specifically made for the mirror-less body (when matching millimeter lenses are available). If cost is not today's buying focus , the long term value gain of image quality plus reduced weight and bulk - Sony becomes a valid choice.

A whole-house jump from Canon to another brand is something I never previously considered. One of those "Who-da' thunk?" moments.

Ed Okie wrote:Question in ignorance: How in the world can an adapter (Canon lens to Sony) still focus at infinity given the adapter's added depth? (I place it in context of three ring lens-extenders used for macro work... infinity is no longer available.

EJ's eye-opening convincing choice of the Sony 7RIII is beyond sobering. After several decades of Canon-equipment professionally used, bodies and lenses... maybe it IS time to move on. In hindsight even corporate Kodak and Kodachrome film came to an end, the Yellow Box once a world-recognized standard.

Downside of adapters if I understand this correctly: the bevy of Canon lenses I have will work... but on a relative basis are bulky and heavy compared to Sigma Art Series or Sony's GM high-end equivalent lenses.

Reading EJ's highly informative lists of "Best Lens" recommendations the Sony and Sigma names appear with stark frequency. (A few years previous I bought the Sigma 35mm f/2.8 Art Series and their computer focus tuning system - it was a eye-opening, even today remains my benchmark of quality, resolution, color, and smoothness of lens-ring focus.)

Logic suggests buy the Sony body and lenses specifically made for the mirror-less body (when matching millimeter lenses are available). If cost is not today's buying focus , the long term value gain of image quality plus reduced weight and bulk - Sony becomes a valid choice.

A whole-house jump from Canon to another brand is something I never previously considered. One of those "Who-da' thunk?" moments.

E.J. will probably explain it much better than I can but I’ll try. 

The Sony distance from the flange mount to the sensor is a lot less than a traditional DSLR because of the lack of a mirror. This allows the use of adapters to retain the sensor to lens focal point distance.  

It all has to do with the flange-back distance, basically the distance from the mount to the sensor.  The Canon EF mount has a flange distance of 44mm.  The Sony E-mount flange distance is 18mm so an adapter that adds 44-18=26mm will allow the lens to focus both at the near point and infinity.  Basically any lens from a system with a flange distance of greater than about 20mm can be adapted to the Sony.  DSLR systems have a much longer flange-back distance since it has to have a mirror box between the sensor and the lens which mirrorless systems do not have.

For example, I have even adapted Leica screw mount lenses from the 1930's to my a7x bodies as that has a flange distance of 27.8mm.

BTW, the Sigma Art 35mm is f/1.4