On Tue, 20 Aug 2002 12:38:18 +0200, "Q.G. de Bakker" wrote:

>Alan Justice wrote:
>
>> To "place the focus exactly where it should be" needs some clarification.
>> Where it should be is the entire depth of the watch. So it seems that it
>> should be placed exactly in the middle (front to back), so that there are
>> in-focus areas in front and behind. If that still doesn't get it all,
>then
>> it can't be done for that framing. Or can it? If you add a 2x TC, then
>> back off to get the same framing, then the DOF would be the same at f32.
>> But the 2x will allow you to go to f64, increasing DOF. Eh?
>
>I agree, sometimes where it should be is the entire depth of the subject.
>But that's not an option in close-up photography... ;-)
>
>When i wrote "where it should be" i meant to say that you should put focus
>there where it makes the best picture, even if the DOF you get wide open is
>all the DOF you will get. Depending on DOF saving the picture will only end
>in disappointing results.
>So no, don't (!) put focus exactly in the middle. Put it there where the
>picture looks best, ignoring what little DOF stopping down will bring.
>Remember too that being in DOF is not (!) the same as being in focus. DOF is
>a term describing 'acceptable unsharpness'. We can debate for hours on end
>what "acceptable" means, but sharp it will never be.
>
>And no: using a teleconverter does not help one iota.

Hmmmm.... I know the theory says no, but in practice, it
does appear possible to "cheat" diffraction at small stops
using converters. In the area of 3X magnification on film,
shot with "normal"-type lenses and not lenses specifically
designed for high-magnification macro, I have been able to
get sharper images around f45-64 effective stop when
using converters (see www.David-Ruether-Photography.com/phun.html,
"Bugs", especially the 4th one...). As for increasing DOF
(or the appearance of it...) in the watch example, using
a lens/bellows with tilt/shift capability can make it
possible to shoot the dial not parallel with the film and
still have it all in focus...