An adapter may well be the smartest accessory there is: for relatively little money you give old or newly purchased lenses a second life on your current camera. Buying used makes extra sense here, because an adapter is a mechanical (and sometimes electronic) little box that carries on doing its job properly, even after years of use.
Check the right direction of the mount
The most important thing with an adapter is the combination: from which lens mount to which camera mount. An EF-to-RF adapter doesn't work the other way round. So always check that the lens side fits your lens and the camera side fits your body. If you want to keep autofocus and automatic aperture control, choose a 'smart' or electronic adapter — a purely manual ring only provides a mechanical connection, fine for vintage glass but without electronic communication. If you're looking specifically at autofocus adapters, the Canon EF-RF Adapter, the Nikon FTZ II Mount Adapter and the Nikon FTZ Mount Adapter are recommended options.
Speed boosters and specials
A speed booster is an adapter with an optical element that compresses the image from a full-frame lens onto a smaller sensor: you gain a little in angle of view and lens speed. You'll also find tilt-shift adapters, close-focus adapters and solutions for using medium format glass on modern systems here. With the optical versions, pay extra attention to scratch-free glass, because it sits in the image path.
Inspection and warranty
Every used adapter is professionally inspected for fit, play and — where applicable — working contacts. You get a minimum 12-month warranty and a 14-day return period, so you can check at your leisure whether the combination with your lens and body does exactly what you want.
