To Adjust the Flange Back Distance

You will need a Flange Back Adjust Chart for this procedure.

The Flange Back Distance (FBD) is the distance between the mounting flange on the camera mount and the film plane. This is the point where the lens focuses the image onto the image sensor. When you install a new lens on the camera mount, or there is an extreme change in temperature, the lens may need to be adjusted.

  1. Set the Iris control on the lens to manual.
  2. Set up the camera and the flange back adjustment chart about 10 feet (3 metres) away from each other.
  3. Open the iris all the way and adjust the light to obtain the correct video input level.
    Tip: If the video level is too high, use an ND filter or increase the shutter speed.
  4. Loosen the setscrew on the flange back adjust ring on your lens.
  5. Zoom in on the chart.
  6. Adjust the focus until the image is sharp. If you are using a flange back adjustment chart, the center of the chart will appear blurry.
  7. Zoom out from the chart.
  8. Adjust the flange back adjustment ring until the image sharp.
  9. Repeat these steps until the image is consistently sharp at both zoom settings.
  10. Tighten the setscrew on the flange back adjustment ring.