Have you ever noticed that your camera’s autofocus seems a bit soft when shooting? Are your pictures as sharp as they could be? Ever buy a brand new lens, only to be disappointed by its sharpness? Ever heard of lens calibration? It's what the pros have done for years.
All cameras and lenses are mass produced & manufactured to fall within certain tolerance range (For example: +/-3). This means that a camera or lens is considered in spec if it falls within that certain range of accuracy. Every manufacturer is different, and has its own set of tolerances, the numbers used in this article are just for example purposes only. Sometimes a lens that is front or back focusing +/-3 is considered acceptable, and within normal operating quality. Very rarely would every camera & lens ship from the factory as perfect (0).
So, if your camera was manufactured and tested by the manufacture to be a +3. That camera would be within acceptable limits and be shipped out for sale. So lets say you buy a new lens and it tested to be a -3. That lens on your camera would make a perfect AF match. +3 + -3 = 0
But what if you had a camera with a +3 and a lens that is also a +3.. That would result in poor autofocus of +6. All your pictures would be on the soft side.
So what can you do? Camera manufacturers can't mass produce every camera and lens to be perfect on every camera ever produced. That's where lens calibration comes in.
Most cameras today, offer a lens AF micro-adjustment option, built right into the camera. This will allow you to calibrate each of your lens exactly to your camera body for the maximum sharpness.
Here are instructions for performing AF adjustments for Canon & Nikon: