Wednesday, October 3, 2012

Accurate and free AF fine-tuning/microadjustment method

Tried this free AF fine-tuning / micro-adjustment method, which I found through a post on DP Review forums:
I found the method to be accurate and fairly easy. Summary: you download the test image, show it on your laptop screen (not print it out). Then you view that laptop screen image with your camera on Live View. You adjust the focus manually in Live View to maximize the moire pattern, resulting in perfect focus. Then you turn off live view, then autofocus with your lens. If your lens is correctly calibrated then the autofocus should not move. If it moves, you adjust AF fine-tuning until it does not move.
Tip 1: To observe whether your autofocus is moving, look at the lens' distance scale as you focus. I find it easier to notice whether the lens is front- or back-focusing.
Tip 2: When you focus in live view, ideally you should use manual focus. However, if your manual focusing isn't good for whatever reason, then you can try autofocus instead. In live view most cameras use contrast detection (not phase detection) which is immune from backfocusing or frontfocusing errors.