On Tue, 20 Aug 2002 23:35:55 GMT, Rudy Garcia wrote:
>In article <3d665b0b.5923100@newsstand.cit.cornell.edu>,
> d_ruether@hotmail.com (Neuman - Ruether) wrote:
>> On Mon, 19 Aug 2002 21:53:49 GMT, Rudy Garcia
>> wrote:
>> >In article ,
>> > "Kevin Neilson" wrote:

>> >> A watch is pretty flat, so I would think you would get enough
>> >> depth-of-field
>> >> on F/32. Remember that the focal range is exponential, so to maximize
>> >> DOF,
>> >> you focus in front of the object, because if the DOF is 3", then 1" of
>> >> that
>> >> is in front of the focal point, and 2" is behind it. Check your DOF
>> >> indicator on the lens.
>> >>
>> >> You could also make a pinhole cover for the lens, but you would get a lot
>> >> of
>> >> diffraction.

>> >Actually, in closeup or macro work the DOF is roughly equally divided in
>> >front of and behind the plane of focus.
>> >
>> >The not very accurate 1/3 in front and 2/3 behind rule doesn't apply in
>> >the macro domain.

>> I don't think it applies at normal distances, either.
>> It does in theory, but equal "out-of-focus" for DOF
>> coverage often looks worse on the far side than it does
>> for the near-side (particularly in landscapes), possibly
>> because the "scale" of the detail is smaller on the far
>> side of focus, requiring greater sharpness for similar
>> subject parts to look about equally sharp on both sides
>> of the actual focus plane...
>>
>> David Ruether

>That is why I refered to it as the "not very accurate ..."
>
>Your observation about the far side out of focus looking worse than the
>near side is correct, but for a different reason.
>
>The treatment of DOF is based around determining the bounding planes
>around the plane of focus, that render subject points as no larger than
>some arbitrary cicle of confusion.
>
>However, a different question can also be asked: How does the diameter
>of the circle of confusion grow for planes successively away from the
>near and far DOF planes? You will find, particularly with longer focal
>length lenses, that the diameter grows at a faster rate for planes
>behind the far DOF than for planes in front of the near DOF. That is
>why you perceive DOF coverage being worse on the far side.
> RG

Interesting...
We should then lay to rest the 1/3-2/3 proportion rule,
it appears, and substitute the 1/2-1/2 rule... It used
to bug me when I saw photos that obviously were made
"by the rules" for universal DOF, but which noticeably
lacked crispness in the infinity-focus parts (due both
to incorrect choice of focus distance and insufficiently
small stop for the image size) - they had a "gooey"
look...;-)