Adjusting The Back Focus of a Lens

In most cases, changing a lens will not require adjusting the back focus of a lens. But when a lens does not hold focus at both ends of the zoom range, you may need to adjust the back focus. By adjusting the back focus, you are changing the distance of between the pick-up device and the rear element of the lens. Technically, it’s the distance from the vertex of the rearmost element of the lens to the focal plane, but we’ll keep it simple. Note that not all lenses have a back focus adjustment.


The Steps

Before starting, put the camera on a tripod and adjust your camera’s viewfinder so it is in sharp focus. Ideally, you’d want a test pattern chart (looks like a dart board) to be at least 75 feet from the camera. Otherwise, as far as possible. If you don’t have a test chart, Use a page from a magazine.

  1. Set the iris to manual.
  2. Set the zoom to manual.
  3. Open the iris to 1.4 or its widest aperture. If the illumination on the test chart is too bright for the open iris, reduce the light or move the chart to a darker area.
  4. Turn the zoom barrel to extreme telephoto.
  5. Focus on the chart.
  6. Set the zoom to wide angle.
  7. Loosen the back focus ring retaining knob.
  8. Adjust the back focus ring for the sharpest focus.
  9. Repeat steps 4 through 8 until focus is consistently sharp.
  10. When it is, tighten the back focus ring retaining knob to secure the ring.

Note: Most lenses are at their sharpest focus at about a middle iris position like F5.6.


Keep Reading...

FAA files model pilot

FAA takes first legal action against model airplane pilot

FAA takes first legal action against model airplane pilot. Raphael Pirker was fined $10,000 for illegally

Read More
Quicktime For Windows Malacious Threat

QuickTime for Windows Vulnerable to Exploit

Trend Micro, the software security company, warns there are two “critical vulnerabilities” in QuickTime for Windows and advises users to uninstall this program immediately. The Homeland Security Department also posted a warning https://www.us-cert.gov/ncas/alerts/TA16-105A based on Trend Micro’s findings and also recommends that PC users remove QuickTime from their systems. Apple stopped supporting QuickTime for Windows, […]

Read More
Robin Williams speaks to the press

The Night I Met Robin Williams At My Front Door

Meeting Robin Williams at my front door.

Read More

A Brilliant Marketing Video For Young Girls

Barbie dolls have often been criticized as a poor role model for young girls. There were comments about Barbie’s unrealistic body standards and a Computer Engineer Barbie who required the help of her male counterparts to get rid of a virus. And there were many other accusations made against Mattel who produced the Barbie doll. […]

Read More


Leave a Reply

Your email address will not be published. Required fields are marked *


  • Forbes Magazine calls VideoUniversity one of the best business-to-business sites for digital video production.
  • WINNER
    Videography Magazine's
    "Website of the Month" Award
  • WINNER
    PC Magazine Online "Best Desktop Video Site" Award
  • WINNER
    CyberFilm School's "FOUR STAR" Award