DOF, Front Focus, Back Focus - HELP!

Started Aug 24, 2005 | Discussions thread
brian thomson Regular Member • Posts: 227
Re: DOF, Front Focus, Back Focus - HELP!

edhannon wrote:

brian thomson wrote:

stop down to the selected aperture. Does this mean that:
a) we are (at least partly) talking about a change in a lens' focus
point at different apertures?

The focus point does not change with aperture. What changes is how
far in front and in back of the focus point a point on the subject
produces a circle less than or equal to the circle of confusion.
That is how far front and back appear to be in focus.

By "focus point" here I'm talking about the lens' actual optical focus point at that time, which would have to be in the middle of the field of focus, surely? I know the mechanical focus position on the body or the lens would not change as the lens is stopped down, the selected focal length would not change.

I thought we were talking about a situation where you've focused on e.g. 1 metre away, but the optical focus point shifts when the photo is actuallt taken?

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brian thomson
dublin, ireland

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