Understanding and Selecting Lens Adapters
You use a lens adapter to fit a lens of another make or mount onto your camera. This feature means you can continue to use your older lenses when you upgrade from one camera to another.
What's a Lens Adapter?
Each camera manufacturer has its own proprietary bayonet fitting for attaching lenses to its cameras. Apart from the mechanical connection, lenses also incorporate a set of electrical contacts that communicate with a processor inside the lens to control focusing, lens stabilization, and aperture.
This degree of complexity means lenses must be designed for one specific camera mount, such as a Nikon, Sony, or Canon lens mount. One exception: lenses with a special screw thread intended for camera T-mount adapters. These are manual lenses such as spotting scopes and telescopes. Although an adapter may have a lens, it's not the same as camera add-on lenses that screw onto the front of existing lenses to change their focal length.
How Lens-to-Sensor Distance Affects Adapters
Each camera manufacturer has a specific flange focal distance, meaning the distance between the lens mount and sensor. When fitting lenses from other manufacturers, the adapter must replicate this distance or, if the flange distance is too short, use an auxiliary lens to focus the image correctly. If not, it'll be impossible to focus on distant objects. This is why a Sony-to-Nikon lens adapter has an auxiliary lens, as does a Sony-to-Canon lens adapter. In addition, some lenses protrude into the camera body, so make sure they don't foul the mirror mechanism or camera body.
Focus and Aperture Control with Lens Adapters
In most, but not all instances, an adapter disrupts the electronic communication between the camera and lens, so features such as automatic focusing, aperture control, and electronic stabilization don't work. While manual focus is possible, unless the lens also has an aperture ring, you can't adjust the aperture, which defaults to its maximum. Some adapters incorporate a dandelion electronic chip that tells the camera you're using an adapter. This allows the camera to confirm the correct focus as it would if you were manually focusing with an OEM lens.
If you have a mirrorless camera and a DSLR from the same manufacturer, you can obtain OEM adapters that provide full lens functionality. A good example is the Sony lens adapter that allows you to mount a Sony A-mount lens to its mirrorless E-mount. Note that you can adapt a DSLR lens to a mirrorless camera, but you can't fit a mirrorless lens on a DSLR.
Choosing a Lens Converter
There are a number of companies selling lens adapters. Some, such as Vello lens adapters, offer a comprehensive selection covering most combinations, while others are more specialized. Apart from adapters for still cameras, several suppliers offer C-mount adapters for cine cameras.
Find the combination you need from the wide selection at B&H Photo and Video.