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...

Ultra Zoom 150 - 600

Ultra-Telephoto Zoom Lens From Tamron

The new Ultra Zoom from Tamron has a focal length of 150 to 600, f5 to f6.3.

Read More
Commercial Drone Use Now Legal

DJI Phantom 2 Vision+ Quadcopter with FPV HD Video Camera

DJI Phantom 2 Vision+ Quadcopter with FPV HD Video Camera, drone, quadcopter

Read More

How To Coil Audio and Video Cables

Thanks to the London School of Sound.

Read More
Produce Video For The NY Times

Produce Video For The NY Times

Get Ready To Produce Video For The NY Times You can produce video for the NY Times. If you can point to a short doc or samples on the web and can pitch an idea, you could produce an OP-Doc for the NY Times. Op-Doc is short for opinionated documentaries. They are typically 5 -10 […]

Read More


Facebook Comments

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Your email address will not be published.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