Jens,
Still muddled, I think. Reading your original statement in light of your
clarification indicates that you STILL think DOF ranges from 2/3 closer (or
ahead) to 1/3 further away (or behind) in respect of the focused distance.
Rather than talking from memory, please do as I suggested and consult the
DOF scale on a lens. Then you will see that the limits of DOF surround the
focus mark on each side by the same distance on the ring, but that the
actual distances to subject represented by these limits are 1/3 closer to
2/3 further away.
e.g. My 35mm lens when focused at 2m and aperture set to f22 has a near DOF
limit of about 1.5m and a far DOF limit of about 3m, i.e. 1/3 of DOF is
ahead and 2/3 of DOF is behind the point of focus. This is an observed
fact.
IOW, along the range of DOF from near to far, the focused point is 1/3 of
the way between the nearest and the furthest "sharp" objects.
In ASCI:
NDOF***************F******************************FDOF
NEAR DOF POINT OF FOCUS FAR DOF
regards,
Anthony Farr
> -----Original Message-----
> From: Jens Bladt [mailto:[EMAIL PROTECTED]
> Sent: Wednesday, 15 December 2004 6:22 AM
> To: [EMAIL PROTECTED]
> Subject: RE: *istD auto focus woes
>
> Nope, Anthony! I meant what I said, but perhaps I express my self badly in
> English. By "ahead" I actually meant "before" the object or closer to the
> camera. By "behind" I meant between the object and infinity. I guess we
are
> really trying to say the same thing :-).
>
> Anyway, I have never done photographs whith the *ist D, where the margins
of
> focus was so narrow, that I have noticed any focusing problems. Perhaps I
> should do some testing?
> Jens Bladt
> mailto:[EMAIL PROTECTED]
> http://hjem.get2net.dk/bladt
>
>
> -----Oprindelig meddelelse-----
> Fra: Anthony Farr [mailto:[EMAIL PROTECTED]
> Sendt: 14. december 2004 05:50
> Til: [EMAIL PROTECTED]
> Emne: RE: *istD auto focus woes
>
>
> Jens,
>
> I think you meant 1/3 AHEAD and 2/3 BEHIND the focusing distance. It's
easy
> to verify this. Look at the DOF scale on a lens (you'll probably need an
> old lens to check this) and you'll see that the far-side limit of DOF
> encompasses more metres, feet or furlongs (as is your wont) between itself
> and the focusing mark, than falls between the near-side limit of DOF and
the
> focusing mark.
>
> regards,
> Anthony Farr
>
> > -----Original Message-----
> > From: Jens Bladt [mailto:[EMAIL PROTECTED]
> >
> > An old rule of thumb used to be, that the DOF lies 1/3 behind and 2/3
> ahead
> > of the focusing distance. So I guess a little behind is perhaps better
> than
> > a little ahead :-).
> >
> > Jens Bladt
> >
>
>
>
>
