You must focus both ends of your video camera lens.
Back focus refers to the adjustment of the rear element of a video lens in relation to its distance from the pickup device in a video camera. Lens manufacturers make their lenses to fit any number of professional video cameras, and the different manufacturing specifications make adjusting back focus a most important necessity. Where normal focusing changes the distance between internal lens elements to adjust for the distance of the subject from the camera, the distance between the rear lens glass and the camera's pickup device must be adjusted precisely and must remain constant.
Instructions
Setup
1. Power up the camera and mount it to the tripod or other stable surface. Connect it to the video monitor (optional).
2. Set the iris for manual operation and adjust it to its widest setting (usually f1.8). Adjust the lighting to the iris setting to avoid an overexposed image.
3. Adjust the camera's viewfinder (or monitor) to the sharpest image.
4. Mount the back focus chart or printed page to a vertical surface at least 50 feet away from the camera.
Setting Back Focus
5. Loosen the back focus ring lock with the appropriate tool (sometimes it requires fingers only). Make sure that the back focus ring turns freely. The video image will go into and out of focus drastically. Position the back focus ring to the clearest focus.
6. Zoom in fully (telephoto) on the back focus chart and, with the front focus ring (used for normal focusing), focus the image.
7. Zoom out fully (wide angle) and adjust the back focus ring to the sharpest image.
8. Repeat the previous two steps, making sure to focus with the front ring only when zoomed all the way in, and with the back focus ring only when zoomed all the way out. When the image does not require further focusing at either end of the lens, the back focus is set.
9. Carefully tighten the back focus ring, making sure not to turn the ring while tightening.
Tags: back focus, focus ring, back focus ring, back focus, back focus chart, distance between