A lens adapter is provided, comprising a cylindrical base, one end of the base is provided with a first mounting seat for connecting with a lens and a manual aperture controlling ring sheathed on the base, the other end of the base is provided with a second mounting seat for connecting with a camera. The lens adapter also comprises an adjusting mechanism connected to a lens aperture controlling rod and the manual aperture controlling ring. The manual aperture controlling ring is adjusted by the adjusting mechanism to make the rotation angle of the manual aperture controlling ring linearly proportional to the size variation of the lens aperture. The lens adapter allows the rotation angle of the manual aperture controlling ring linearly proportional to the size variation of the lens aperture in a manner of synchronously changing, thus facilitating the user to control the lens aperture.