Is there something I am doing wrong with Fuji's AF?

Started Mar 18, 2013 | Discussions thread
Adrian Tung Veteran Member • Posts: 3,278
Re: Is there something I am doing wrong with Fuji's AF?

Photozopia wrote:

Like nixda says, Fuji's have a tendency to lock on the 'wrong bit' of a focus box that overlaps near/far objects. Practise is the only real trick ... even AF Lock is easily fooled by an 'overlapping' focus box.

It's actually more predictable than that.

A contrast detect system only detects contrast. In order to start focusing, the lens has to start moving in one direction -- generally towards infinity. If your lens was already focused at a distance beyond your subject, it will keep going towards infinity and find constrast in the background before ever doubling back and reaching the subject.

This is where phase detect pixels help -- if they are active, they are more likely to detect a closer subject and tell the focusing algorithm to move the other way instead.

This won't help in strongly backlit situations though, because due to limited dynamic range the bright background will overpower the foreground. What the sensor sees will be a dark shadowy shape surrounded by very nice and bright details. So guess what it will try to lock on?

Of course, the best solution is to control the position and size of the AF box to avoid overlapping with unwanted features that the AF system may lock on.

 Adrian Tung's gear list:Adrian Tung's gear list
Nikon Coolpix A Canon EOS 10D Canon EOS 5D Mark III Sony Alpha a7R Canon EF 35mm F2.0 +12 more
Keyboard shortcuts:
FForum PPrevious NNext WNext unread UUpvote SSubscribe RReply QQuote BBookmark MMy threads
Color scheme? Blue / Yellow