Back Focus

Occasionally when filming you will find that if you zoom in and focus on a subject and then pull out wider the image will go out of focus. If this happens it is likely that the back focus is out. This is easily remedied by following this simple procedure:

The Procedure:


Before you start, mount your camera on a tripod and adjust your camera's viewfinder to achieve sharp focus.

Ideally, you should place an object at least 25 Metres from the camera or as far from the camera as possible. Set the iris to manual

  1. Set the zoom to manual
  2. Open the iris to its widest aperture - If the illumination on the object is too bright for the open iris, reduce the light or move the object to a darker area
  3. Zoom fully into the centre of the object (maximum focal length of the lens)
  4. Focus on the object
  5. Zoom out fully
  6. Loosen the back focus ring retaining screw
  7. Adjust the back focus ring for the sharpest focus
  8. Repeat steps 4 through 8 until focus is sharp throughout the zoom range
  9. Tighten the back focus ring retaining screw to secure the ring

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