DOF, Front Focus, Back Focus - HELP!

Started Aug 24, 2005 | Discussions thread
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edhannon Senior Member • Posts: 1,761
DOF, Front Focus, Back Focus - HELP!

All these threads on DOF, Front & Back Focus have me very confused!

Let me put in my own words what I thought I understood before all this. Then maybe someone with a lot more experience than me (like Godfrey) can get me straight.

I thought DOF depended on three things: the subjective opinion of the viewer of what is sharp, the size of enlargement, and the geometry of the "circles of confusion". By the last one I mean the size of the circle projected on the film/sensor by a point in the subject.

I don't think that the first two have nothing to do with the lens/camera so I will ignore them in this.

I thought that the the size of the circle is only a function of the lens focal length, the aperture selected and how far the subject is from the center focus plane.

I can't see how the lens or camera allignment can effect how far front or back of the center focus point that a subject appears in focus.

What I can see is how the center focus point can be different from what I think it is. In manual focus I do not allways manage to focus where I think I am focusing. In auto focus I seem to focus where I don't want to more than in manual focus!

So are not front/back DOF issues really mis-focusing issues?

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