If you are wondering about how to calibrate lenses, this article has detailed explanations and different methods of AF fine tuning. Due to the nature of the phase detect autofocus system that is present on all SLR cameras, both cameras and lenses must be properly calibrated by manufacturers in order to yield sharp images. Various factors such as manufacturer defects, sample variation, insufficient quality assurance testing/tuning and improper shipping and handling can all negatively impact autofocus precision. A lot of photographers get frustrated after spending thousands of dollars on camera equipment and not being able to get anything in focus. After receiving a number of emails from our readers requesting help on how to calibrate lenses, I decided to write this tutorial on ways to properly fine tune focus on cameras and lenses.
Why is there a need to calibrate lenses? With the release of new, high-resolution cameras like Nikon D800, it seems like calibration is becoming an important and hot topic. As I have explained in a number of my photography articles and reviews, while the increase of megapixels in our cameras has a number of benefits (see benefits of high resolution cameras), it can also expose potential focus problems. A slight focus issue might not be as noticeable on a 10-12 MP sensor, but will be much more noticeable on a 25+ MP sensor (assuming both sensors are of the same size).
While landscape and architectural photographers might not care about focus issues (since they photograph at very small apertures that hide small focus issues), portrait, event and wildlife photographers are typically much more worried about focusing problems. I personally like to photograph people wide open with my lenses, which can be a challenge for obtaining perfect focus on my subjects. How frustrated would you be, if you focus on someone’s eye and you get their nose or ears in focus instead?
The process of calibration involves going through a specific camera setting that allows fine tuning autofocus operation of lenses, which means that we will NOT be changing anything on the actual lens. Physical calibration of lenses should only be performed by manufacturers, since lenses have to be disassembled, tuned and reassembled.
As I pointed out in the phase detection autofocus system and how to test your DSLR for autofocus issues articles, the source of autofocus problems could be an improperly calibrated camera, a lens or both. The way calibration works, is the camera has a setting, which allows compensating for either back-focus (when focus is shifted behind the focused area) or front-focus (when focus is shifted in front of the focused area). This compensation can be performed in small incremental steps (typically from 0 to -20 and +20 in steps of 1), which allows for precise fine tuning of the autofocus system. Negative numbers compensate for back focus, while positive numbers compensate for front focus problems. To put it differently, dialing a negative “-” number will move the focused point closer to the camera, while dialing a positive “+” number will move the focused point away from the camera. The camera tells the lens something like this: “aim at where you would normally focus, except slightly move the focused point closer to the camera”. In essence, this would be needed when your camera and lens combination constantly back-focuses.
An important fact to keep in mind, is that calibration is camera and lens specific, which means that if you have multiple cameras and lenses, you have to fine tune autofocus on each camera, for each lens you own (unless you have a camera that constantly front-focuses or back-focuses by the same amount with all lenses, in which case you might need to compensate only for the camera itself). In addition, you might need to periodically re-calibrate your camera gear (more on this below).
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