Are your lenses focusing where they should? In our latest DIY Photography Hacks post we show you how to make an AF micro adjustment to get spot-on autofocus with any camera-lens combination
When your viewfinder’s autofocus points turn red and your digital camera beeps, you know your focusing is bang on. Or is it?
Unfortunately, some camera-lens combinations don’t focus as accurately as you’d hope, and a lens that works fine on one camera body may be slightly off on another.
What we’re talking about isn’t so much a focusing issue, but the fact that autofocus may not stop at precisely the correct place.
You may have heard about ‘front-focus’ or ‘back-focus’, and the problem manifests itself with your depth of field not extending in front of and behind your subject correctly, or with ‘soft’ images when shooting wide open.
Need some space
The Datacolor SpyderLensCal will diagnose focusing issues with your camera and lens, so you can then use the AF micro adjustment custom function found on some DSLR models to correct for pin-sharp focus.
You’ll need space; it’s recommended to have 50x the focal length of the lens – that’s 15 metres for a 300mm lens! You also need a brightly lit area to place the photo target, as autofocus will have to accurately lock on.
You’ll also need two tripods: one for the camera and the other to set up the target, aligned to the same height and square-on to the lens. There’s a bubble level on the target to aid precise positioning.
The whole setting can be performed on the camera’s LCD, but it’s best to check the images on a computer.
Short sharp shot
But is it worth doing? We tested six lenses on two camera bodies and none had serious focusing issues. If you suspect focusing problems, however, as images aren’t sharp where you want them, it’s relatively easy to test your system.
On shorter focal-length lenses, especially ones without very wide maximum apertures, it’s hard to identify the exact point of focus on the scale, but it gets much easier with longer focal-length lenses.
Unfortunately, not all camera models allow you to fine-tune autofocus in this way. If your camera has focus problems but doesn’t enable you to perform AF micro adjustment, try an authorised service centre.
The DIY Photography AF calibration solution
How to make your own AF calibrator using a ruler!
It’s perfectly possible to make your own focus calibration aid – all you need is a ruler positioned at a 45º angle placed next to a chart to focus on; use the central mark on the ruler aligned with the target as the point to get in focus.
Another option is to use tethered shooting, aiming the camera at your computer monitor and shooting a specially designed on-screen target and checking the resulting moiré patterns.
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