How to calibrate your lens.
The calibration process involves taking a series of photos in a controlled way, so you can see exactly how your focus is off. You can then correct it using your camera settings. If the intended subject of your image is blurry, that means your camera is either back focusing or front focusing. A back focus is when the focus falls slightly behind your subject and a front focus is when the focus falls slightly in front of it.
When you calibrate, you’re telling your camera to shift the focus one way or the other when it does the imaging, so your final photo matches what you see in the viewfinder or screen when you take it.
Lens calibration tools and setup.
To calibrate, you need a well-lit environment, a tripod, a flat surface, and a subject to photograph that has easily measurable markings. You can purchase special objects to use as the subject of your test photos, which have been specifically designed to help you find your focus, such as focus pyramids or calibration charts. Or you can create your own prop.
One method is to use a hardcover book and a 12-inch ruler with clear markings. Stand the book up on its bottom edge, so the cover is facing the camera. Tape a small piece of paper with an “X” drawn on it to the front cover at the center line. Then balance the ruler against an object, like a coffee mug, so it’s at a 30-degree angle. You want the ruler placed right beside the book, with the top end tilting away from the camera, and the middle 6-inch point lining up against the center of the book cover where you’ve taped the paper.