RE: [Leica] how can the 75 Lux focus go bad?

["Austin Franklin" <austin@darkroom.com>]

> >> http://www.silverlight.co.uk/resources/dof_calc.html
> >>
> >>> From: "Austin Franklin" <austin@darkroom.com>
> >>>
> >>>> Wide open and focused close, the depth of field of the 75/1.4
> >>>> is between 6mm
> >>>> to 8mm (just over a quarter inch).
> >>>
> >>> What are you basing this number on?
> >
> > I don't believe it's accurate.  I routinely shoot at 1.4
> with both a 75 and
> > an 85, and I find my critical DOF to be much much larger
> than 6mm to 8mm.  I
> > also print typically 13x19...so DOF is quite noticeable.
>
> Again, DOF is a perceptual effect, not a physical property of
> the world.  It
> is based upon the perceived zone of sharpness around the
> plane in focus and,
> as such, is affected by how good your vision is, how large is
> the print, and
> the viewing distance from that print.

> When DOF is calculated, it is based upon normal viewing
> distance (I forget
> exactly what this is) of an 8x10" print and the "normal"
> human acuity of
> 0.2mm, which translates into circles of confusion in the 35mm
> negative of
> 0.03mm.

Thanks, I've been doing this professionally for more than 25 years...I know
what DOF is, and what sharp etc. is.  I assure you, the DOF of the 75/1.4,
my most used lense, if FAR more than 1/4".  My typical image these days is
shot at 3 feet, and printed at 13x19.  If the DOF was only 1/4" you could
NEVER focus on a particular part of a human.  Humans move more than 1/4"
just breathing...especially one year olds.

Cripes, just go take a picture and see for your self!