Why Do You Need a Lens Calibration Tool?

It is a fact of life that camera bodies and lenses don’t always play well together. Most cameras and lens combinations suffer from a bit of front or back focus, meaning the lens doesn’t focus accurately on the subject.  This is most obvious when using long lenses and wide apertures.  Most cameras and long lens combinations can benefit from some focus tweaking. Your camera body needs to have micro-adjustments in the menu system. If you are using normal to wide angle lenses at medium to small aperture settings (f/8 to f/16), front or back focus doesn’t matter because you have plenty of depth of field to cover for any focusing errors. But, if you are using longer lenses at wider apertures to focus wildlife or sports, front or back focus can cost you much needed sharpness in your images. The good news is you can do your own lens calibration after purchasing this tool. 

To use a calibration tool: 

  • Set up your camera on a tripod so the sensor plane in your camera is parallel to the auto-focus target of the lens calibration tool.  
  • With most calibration tools the camera sensor plane needs to be at a distance of 25 times the lens focal length from the calibration tool.  

                      o 18mm lens that is between 40 cm and 50 centimetres 

                      o 55mm lens that is between 1.00 m and 1.5 meters 

                      o 300mm lens that is between 7.5m and 8 meters 

                      o 200mm lens that would be about 5 meters. 

  • When testing a zoom lens test at both ends of the lens settings. 

                      o 18-55 or 18-350 and 55-300  

  • Auto-focus on the target.  
  • Once the lens has focused turn off the auto-focus.

IMPORTANT : Use mirror lockup and a self timer or shutter release to eliminate vibrations and take a picture.  

  1. Open the photo on your computer and look at the image at 100% (actual pixels) magnification.  
  2. Check out the sharpness of the lines on the Focus Calibration Tool Alignment Ruler.  
  3. If the zero line (the line that is even with the focus target) is the sharpest, the camera and lens combination is good to go.  
  4. If one of the other ruler lines is sharpest, your camera/lens combination is front or back focusing.  
  5. You will need to go into the camera’s menu system, make a change to the micro-adjustment for that lens.  
  6. Repeat the whole process again by taking another picture.  Check out the photo again.  

Repeat the process until the zero line is the sharpest line. With zoom lenses you do this at both the longest and shortest focal lengths.  Your camera can store each lens and its micro-adjustment settings in its memory.  If you have more than one camera body, you will need to test your lenses on each body.

This image displays accurate focus

Here you can see a slight bias to the rear of the focus line

 

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