Follow focus

A focus puller or focus device (English Follow Focus ) is a attached to a camera lens apparatus with which the distance scale of the lens to be moved and thus the focus of the image plane can be changed.

While lenses from still cameras the distance setting can be performed easily at the distance setting, this is for film cameras that take continuous image sequences, difficult as you want to avoid that the audience in the cinema or watching television uneven change or even break ( if the ring must change hands ) notices of focus, or even the camera is miterschüttert from touching the lens.

For this reason, focus devices have been developed which allow a uniform liquid change of focus without the lens needs to be touched directly. In the simplest case, there is a attached to the focusing ring of the lens, projecting pin, which can be moved back and forth.

In the professional field, however, have now become established focus units, in which the distance scale through gears and sprockets is connected to a rotating wheel on which, for example, the camera assistant rotates to change the sharpness level. Special lenses for movie cameras have usually via a permanently attached / integrated ring gear, while it is attachable gear rings for other lenses, for example in the field of video DSLRs. A gear on the focus system intervenes in this sprocket. The gear, in turn (possibly via further gear wheels) is connected with the rotary ring. To adjust the focus puller for different lens diameter, the gear is mounted on a pivoting arm. The entire focus puller must also be mounted in a position that is invariant to the lens. This is usually achieved by both the camera with the lens and the focus puller on a support system (eg, 15 -mm or 19 -mm light-weight supports ), called rods, are attached.

To ensure compatibility between lenses and focus pulling devices, is the tooth pitch of lens ring gear and is standardized eingreifendem gear, but there are several standards. In the cinema art teeth are common with a modulus of 0.8 (corresponding to a tooth pitch of about 2.51 mm).

A similar device is also available to adjust the iris to the lens.

• Cine - Standard
• Camera technology