What’s the best way to calibrate a lens for autofocus accuracy?

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December 19, 2014 at 10:06 am  •  Posted in Q&A, Tips & Techniques by  •  0 Comments

A friend sent me a link to an article on the Internet about the need to calibrate lenses so they will autofocus with 100% accuracy? But if this is so important, why has it not gotten more coverage? Also the calibration process seems very complicated. Can you provide a simpler method for AF fine-tuning with a DSLR camera?
Allen T.

This topic is complex, Allen, and it would require a lengthy discussion of the concepts and the solutions, step-by-step, but here’s a brief summary. Yes, it is possible that a certain lens might need calibration to force it to autofocus with 100% accuracy. Any slight focus inaccuracy is most noticeable in images made at a very wide aperture (such as f/1.8 or f/2.8) using a camera with 20+ megapixel resolution. Because only one of my oldest lenses exhibited a focusing problem with a 36-MP Nikon D800, I cannot comment as to whether many others require fine-tuning for optimal autofocus.

A lens should provide razor sharp focus on the area where you focused in AF mode, such as the hawk's eye in this image. If your lens does not seem to be providing maximum accuracy, you'll want to confirm that and make any required correction. Frankly, many images are soft overall, and that's caused by other problems such as blurring from camera shake.  (At 300 mm; f/2.8) © 2013 Peter K. Burian

A lens should provide razor sharp focus on the area where you focused in AF mode, such as the hawk’s eye in this image. If your lens does not seem to be providing maximum accuracy, you’ll want to confirm that and make any required correction. Frankly, many images are soft overall, and that’s caused by other problems such as blurring from camera shake. (300 mm; f/2.8) © 2013 Peter K. Burian

Many recent DSLRs of all brands include a feature that allows for lens calibration, called AF Fine Tuning by Nikon and AF Microadjustment by Canon, for example. This process is necessary only when a lens produces back-focus (setting focus at a point behind the intended plane) or front-focus (setting focus at a point in front of the intended plane). Both companies provide technical information about their specific technologies as discussed in these articles: AF Fine-Tuning – Technical Solutions, How to use the AF Fine-Tune function (Nikon), and AF Microadjustment: A Detailed Look (Canon).

Note: The following comment from Nikon is relevant to any camera and any lens, regardless of the brand: “It’s important to remember that AF Fine-Tune [or whatever term is used by the camera brand that you own] is an adjustment specific to the camera and lens combination under test. The adjustment has to be repeated should you need to adjust another lens with the same camera body or another camera body and lens combination.”

The lens calibration feature has its own name depending on the brand of camera. If it's available in your DSLR's menu, the focus test/calibration process is straightforward when using a kit such as the Datacolor Spyder LensCal. Photo Courtesy of Datacolor

The lens calibration feature has its own name depending on the brand of camera. If it’s available in your DSLR’s menu, the focus test/calibration process is straightforward when using a kit such as the Datacolor Spyder LensCal. Photo Courtesy of Datacolor

These articles provide an indication as to how you can find the pertinent Menu item and how you can do a basic test to determine whether a lens might require AF fine-tuning or Microadjustment. That requires a focus target and a measuring scale designed specifically for this purpose. The most readily available kit, the Datacolor Spyder LensCal ($80), definitely works well. Check out Datacolor’s SpyderLensCal – YouTube video which makes the process straightforward, if not necessarily “simple.” While a Canon EOS camera is used for the demonstration, the method is similar with DSLRs of other brands, so this tutorial should be valuable regardless of the equipment that you own.

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