DOF, Front Focus, Back Focus - HELP!

Started Aug 24, 2005 | Discussions thread
OP edhannon Senior Member • Posts: 1,761
I think I have it now

After all the responses, I think I have an understanding of what is going on:

1. The threads about back/front focus are really talking about where the AF decides the plane on which it will focus is located. I got confused with terminology when some talked about how much was in focus in back of the focus plane vs how much in front.

2. DoF is not an absolute concept. It varies depending on a lot of variables: the viewer, amount of enlargement (on screen or on print), etc.

3. I learned that how much is in focus in back vs front is not constant but varies depending on lens focal length and distance. Thus the location of the plane of focus is not easily judged by looking at the front and back edges of the DoF.

4. The only physical constant in all this is that, for a given focus setting on a lens (distance from sensor), there is only one plane parallel to the sensor that is really in focus.

5. AF is even less deterministic than I thought. Only the Shadow knows where it will lock. Another reason for me to avoid AF as much as I can.


 edhannon's gear list:edhannon's gear list
Pentax K10D Pentax K-3 Pentax smc DA 16-45mm F4 ED AL Pentax smc FA 77mm 1.8 Limited +1 more
Post (hide subjects) Posted by
Keyboard shortcuts:
FForum PPrevious NNext WNext unread UUpvote SSubscribe RReply QQuote BBookmark MMy threads
Color scheme? Blue / Yellow