It depends entirely on what the adapter carries, and that is published per adapter rather than implied by the two mounts. A purely mechanical adapter passes nothing, so aperture and focus become manual.
An adapter is a spacer with a fitting at each end. Everything beyond the mechanics is an addition its maker chose to include, and publishes.
The mechanical part, which is arithmetic
Flange distance decides the direction. Adapting a lens built for a longer flange distance onto a body with a shorter one works, because the adapter supplies the difference. The reverse fails at infinity focus and no adapter fixes it — this is subtraction, not engineering.
The electrical part, which is a list
Contacts differ between systems, so nothing passes automatically. What an adapter carries is stated by whoever made it:
- aperture control, without which the lens sits at one opening;
- autofocus, with whatever speed and accuracy the pairing allows;
- stabilisation signalling, where both ends support it;
- lens data, which is what writes the focal length into the file.
A listing naming some of these has claimed those and not the others. A listing naming none has claimed nothing at all, and that is how this site records it.
The third kind, which changes the picture
Some adapters contain glass — a teleconverter multiplies the focal length, and a focal reducer shortens it. Those are optical devices with their own effect on aperture and sharpness, and they are a different purchase from a spacer.
What people ask before they commit
Why can a mirrorless body adapt almost any older lens?
Because its flange distance — the gap between mount and sensor — is shorter, and an adapter can only add distance, never remove it. A lens designed for a longer flange distance can therefore be moved back to where it expects to sit. In the other direction no thickness of adapter recovers focus at infinity, which is arithmetic rather than a limitation of manufacture.
Is a more expensive adapter always better?
It is usually carrying more: contacts, a motor, sometimes optics. What matters is the list of functions the maker states — aperture control, autofocus, stabilisation signalling, lens data — because a listing that names none has not claimed any. Price is a proxy for that list, not a substitute for reading it.
Last reviewed 12 September 2026