In the field of film production, the focus star is often called a “back focus chart” or “Siemens Star”. The star is widely used to adjust the back focus of removable lenses. It is also used during film or video shoots to help setting the focus in special situations.
How to Adjust the Camera Back Focus by Media Collage
- Set your camera on a tripod or stable mount, with your subject (back focus chart or other contrasting object) at least 20 metres/70 feet away (or as far as possible).
- Your iris should be wide open, so it’s better to perform this operation in low light. Alternatively, add some shutter speed or a ND filter.
- If your lens has a 2X extender, switch it to 1X.
- Zoom in on your subject.
- Adjust the focus normally until the picture is sharp. If you’re using a back focus chart, the centre of the chart will appear blurry – your focus is sharpest when the blurred circle is smallest. (You can simulate this effect by looking at the chart above and defocusing your eyes.)
- Zoom out.
- Loosen the back-focus ring’s locking screw, and adjust the ring until the picture is sharp.
- Repeat steps 3-6 until the focus is consistently sharp.
- Tighten the back-focus locking screw.