DEAR RICHARD ET ALIA,
As most images shot in cinema/video are shown at much larger magnifications
(cinema screens or large screen monitors; pads and smart phones excepted) than
still photos, the tolerances for cine/video depth of field are much tighter
than for pictorial photography. Also, reflex viewfinders do not give you enough
magnification to see if the extremes of fg and bg will look sharp enough when
viewed on large screens. Yes, the definitions of DOF are approximate and
defined by "acceptable sharpness" but directors of photography have bowed to
this goddess for maaaaaaaaaaaaaaaaaaany decades and continue to do so.
On a smaller, more personal scale, I love to make 16X20 prints from images shot
with my 'Blad on film. DOF scales for still photography are based, IIRC, on
viewing an 8X10 print from less than about arms length. I learned the easy way
at RIT in my first optics class that these scales would not suffice if I were
making larger prints to be viewed from the same or less distance. I learned the
hard way in 1975 when I bought my first blad and did a shot that looked tack
sharp in the view finder that, when I made a lovely 15X15 inch print from the
neg that the fg and bg were sliiiiiiiiiiiiightly soft even to the naked eye at
about arms length. As you know, the 'Blad lenses have those moving red lines on
each lens's distance scale that show you your alleged DOF at that f stop and
distance. I have always added one f stop (or more with longer lenses) to what
they showed as acceptably sharp and have been happy ever since.
CHEERS!
BOB
From: "`Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
To: "pure-silver@xxxxxxxxxxxxx" <pure-silver@xxxxxxxxxxxxx>
Sent: Thursday, August 18, 2016 5:02:15 PM
Subject: [pure-silver] Re: Large Format Metering at the Groundglass
Interesting to know. T stops insure that exposures made with any of several
lenses will match. Depth of field is a geometric property so, unless all the T
stopped lenses have about the same difference from the f/stop the charts won't
be quite right. In any case, depth of field is very approximate, that is, it
really has no fixed definition other than what is perceived to be sharp, so
variations in charts, unless very large, are of no consequence. In most cases
modern motion picture cameras have through the lens reflex finders so one can
see what the depth is visually rather than guessing from charts.
On 8/18/2016 1:31 PM, bobkiss caribsurf.com wrote:
DEAR RICHARD ET ALIA,
As I still do some work as a director of photography on film/video productions
and teach film/video production, I can state that video/cinema lenses intended
for professional production are still calibrated in T stops. The local
production houses' lenses are calibrated in T stops and the Barbados Film and
Video Association has a lovely set of brand new, coated prime lenses for their
Black Magic 4K cameras, all calibrated in T stops.
Further, depth of field tables for cinematographers are also calibrated in T
stops and meters and/or feet. I just viewed some tables for Zeiss prime cine
lenses.
CHEERS!
--
Richard Knoppow dickburk@xxxxxxxxxxxxx WB6KBL
