Here’s my evolving article on how to best calibrate your digital slr for best focus.
So you have your shiny new Canon or Nikon dSLR and a set of equally shiny lenses. You’ve spent a lot of money and want to get the best of them? You want to make sure they all work as you’d expect and more importantly focus where you want them to? Of course you do. You’d expect everything to work 100% out of the box right? Well sometimes it will sometimes it won’t.
My camera front focuses/back focuses or sometimes misses completely! Sometimes this is human error, sometimes the camera is at fault. We could be moving. The subject could be moving. There could be low contrast on our subject and the camera focuses on high contrast behind our subject. Contrast is what allows us to focus. If you’ve ever tried to focus on a large blank wall of the same colour you’ll see
Why won’t my camera and lens focus perfectly every time?
Well the camera’s autofocus system has a certain tolerance for what it thinks is “in focus”. If it’s in focus then thats deemed good enough. As you can imagine when the camera tells us it’s in focus it may be ‘close’ but it may not be 100%. Coupled with todays much higher resolution sensors and AF if fighting a tough battle indeed.
How can I make my lenses focus better?
Well Canon and Nikon (and some others) added an ability to store an AF offset for each lens you mount on the camera. The offset can be zero. Any typically ranges from -20 to +20. The problem is how do you know what to set these to? one set of values moves the focus point towards the camera and the other values set it further away.
Well initially you have to do it by trial and error by adjusting the values and seeing if it made your focus is now in the correct place or not. This was initially done by photographing a ruler or something and then moving the AF point backwards and forward until you were in the right place. The problem with this is that it’s time consuming and you go half blind staring at the ruler working out if it is now better or worse than before.
Some of the reason for this is the built in variation with the Cameras AF system. Some errors are due to the camera and lens calibration being off, and some due to AF errors (all systems have errors unfortunately). So how do you work out which are errors in the AF system and which are differences in calibrations?
Well I’ve been using Reikans FoCal for years now. I love it so much that I offer calibrations in my studio. After trying the alternatives none are as reliable, repeatable and take into account field curvature of lenses, AF errors, AF consistency, test conditions changing etc. FoCal simply makes it so easy. The only downside to FoCal is that it looks really complex when you first look at it. Especially the PRO version (this is by far the best version to get). In reality it’s super easy. I’m going to add some videos that will show you how easy it really is to use.
FoCal Target Setup
I use the FoCal Hard target and double sticky taped to a noticeboard so i know that it’s nice and flat.
Great news now where can I buy FoCal?
Head over to the Reikan FoCal website, check your camera is compatible and but the electronic download. You’ll want to calibrate every lens before you use it in anger.