A simple autofocus target (free for downloading)

Started Apr 16, 2012 | Discussions thread
ForumParentFirstPreviousNextNext unread
Flat view
Julian Vrieslander
Contributing MemberPosts: 937
Like?
A simple autofocus target (free for downloading)
Apr 16, 2012

Some people are running tests using autofocus targets that might be less than optimal. For example, a starburst pattern can be useful for evaluating sharpness, but when used as a target for a phase detection AF system, the results might be somewhat sensitive to the exact aiming position.

In a message elsewhere on this forum (I lost track of the link), someone showed a photo of a focus test rig at a Nikon service center. The focus target in that rig was a simple series of alternating white and black vertical bars. The width of the bars varied, to prevent errors caused by shifts of one or more pattern cycles.

I made some targets based on this design, and it seems to work well on the line and cross sensors in the Nikon PDAF system. You are welcome to try it out. Here is a file with the graphic:

http://julian.marmotandweasel.com/photos/AF_target.pdf

The file contains three of the targets on an 8.5x11" page. I recommend printing it on a good inkjet. The black background of one target should measure about 100 x 60mm. If you position the target on a plane parallel to the image plane of the camera, and at a distance 50x the focal length of your lens, the target will be approximately the right size to fill one of your focus brackets (at least, for the cameras I have tested recently: D700 and D800).

ViewNX and CaptureNX can be configured to display the selected focus bracket for a shot. This is a 100% crop from a screenshot in ViewNX, showing one of my targets under a focus bracket.

Here is a set of shots showing the setup I used to test the sensors in my D800. I'll describe the details of my test procedure, and the results, in another post.

http://julianv.zenfolio.com/p260391664

Nikon D700 Nikon D800
If you believe there are incorrect tags, please send us this post using our feedback form.
ForumParentFirstPreviousNextNext unread
Flat view
ForumParentFirstPreviousNextNext unread
Keyboard shortcuts:
FForum PPrevious NNext WNext unread UUpvote SSubscribe RReply QQuote BBookmark post MMy threads
Color scheme? Blue / Yellow