Autofocus Calibration



August 2015

DIGITAL SLR AUTOFOCUS CALIBRATION
I realised today that I haven't calibrated my camera's autofocus recently. Keeping your lenses calibrated so that they focus on the correct plane is essential to producing pin sharp images. No matter how good your technique is, if you use the autofocus system on your camera to focus and it is not focusing in the correct place, then this will virtually always produce soft images.

I thought it would be useful to see how far out a lens can be. The two images below (to the left) show the extremes of bad focus that lenses can be set at when attached to our camera, often without us even knowing it.

1. The image below to the left shows an out of focus lens where the autofocus point is almost 2 centimetres in front of where it should be.
2. The central image shows an out of focus lens with the autofocus point 2 centimetres behind where it should be focusing.
3. The image to the right has been correctly calibrated using the Lenscal focusing device so that the autofocus point falls in the middle of the scale - correctly focused!



Of course the calibration is carried out in-camera, so it's actually fine tuning the camera rather than the lens.