| 摘要 |
A conversion arrangement for mounting optical units on a camera such as a film or television camera has a generally cylindrical mounting body (12, 14) for attachments to the camera body, a generally cylindrical carrier (B) for attachment to the optical unit, the carrier being co-axially coupled to the mounting body for axle movement relative to the mounting body, and a focusing ring (22) which is co-axial with and coupled to both the mounting body (12, 14) and the carrier (B). The focusing ring is rotatably relative to the mounting body and carrier to move the carrier axially off the mounting body to focus the optical unit. Backlash during focusing is reduced to negligible proportions by use of a screw-thread arrangement in which a screw-thread is formed on a radially inner wall of the focusing ring by means of a wire coil (44), the pitch of the wire coil being set by end members (46) and gapped rings (48) acting as spacers between the turns of the wire coil. Several followers (30) are supported on the carrier and engage with the wire coil so that rotation of the focusing ring winds the followers and therefore the carriage axially along the focusing ring in order to effect focusing. This screw-thread arrangement avoids the need for very precise machining of the screw-threads on the focusing ring (22) and carrier (B) and provides for simple replacement of the followers (30) in the event of wear or damage. |
