Bob….
In the days of yore, my mentor in insisted the the proper viewing distance of a
print
was… still is?) the factor of the focal length of the lens that was used to
expose the negative
multiplied by the linear 'enlargement' of the print.
[But… that was 60+ years ago… and 'things' may have changed since then 8-)]
Ken
On 2016-08-18, at 3:19 PM, "bobkiss caribsurf.com" <bobkiss@xxxxxxxxxxxxx>
wrote:
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
