[rollei_list] Re: Meters and Film
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <rollei_list@xxxxxxxxxxxxx>
- Date: Tue, 1 Sep 2009 13:51:09 -0700
----- Original Message -----
From: "Carlos Manuel Freaza" <cmfreaza@xxxxxxxxxxxx>
To: <rollei_list@xxxxxxxxxxxxx>
Sent: Tuesday, September 01, 2009 7:48 AM
Subject: [rollei_list] Re: Meters and Film
Spot metering is useful for selective meter readings, it
depends about the subject characteristics, if you use it for
a wide subject you could need to take several readings and
to decide an average, it means you are using more time to
measure the light; as Richard K wrote yesterday, you need to
know what to do with the spot reading according the idea you
have on the subject composition.
The dome for the incident light readings represents the
subject and the light inciding on the dome is the light
falling on the subject as seen from the camera position,
this is very useful for backlight scenes because the
lightmeter takes a general reading about the subject in
shadows ignoring the illuminated background maintaining the
backlight effect on the subject, a spot metering would work
similar for this case, however you could need more than a
reading to be sure about the exposure if the subject is
large, and incident light reading is quicker than a spot
reading for similar cases.
Carlos
The Sekonic meter is interesting. It has three
attachments for measurement, a grid, for reflected light,
and two diffusers for incident light, a flat one for
measuring single sources and a dome or hemisphere for giving
a sort of averaged reading depending on the location of the
light with regard to the camera angle. I am at the moment
drawing complete blanks on the name of the fellow who came
up with this idea and the original name of the meter. It was
intended for motion picture use originally. The reflected
light grid was meant for measuring the subject contrast
using close readings. The flat diffuser was intended for
measuring lighting ratios, i.e., the relative brightness of
key vs: fill light, and the dome for overall exposure. The
latter makes an assumption I am not sure is valid. That is,
that the correct exposure for a subject or scene should be
based on the average of the light striking it from various
angles rather than the actual brightness of some fixed
reflectance value. As an example, suppose one has a mostly
back lit low key scene where most of the dome is shadowed
when pointed from subject to camera (this is how the thing
is to be used). The result will be an exposure essentially
for the shadow areas whereas, for low key, one wants the
exposure to be essentially for the highlights even though
they may occupy only a small area of the scene. Since the
brightness of areas of subjects may be independant of the
angle of the light a meter of this sort may be quite
misleading as to correct exposure.
Another thing which bothers me is the adjustment of
negative contrast according to scene contrast. This may be
useful in insuring that the film records the full range of
brightness in the scene but may be misleading when printing.
There are scientific uses of photography where a low
contrast negative may be desirable because some detail is
wanted in both fairly dark shadows and in fairly bright
highlights. However, the full contrast range of such a
negative can not be reproduced by any normal printing
method, especially not by reflection prints to be
illuminated by ambient light (as opposed to being in a
light box). The Zone System worries a lot about "placement"
of various densities on negatives and on prints but doesn't
seem to take into account that contrast can be adjusted in
the printing step and sometimes must not be linear as when
burning and dodging are done or masking using variable
contrast paper. For instance, some of Ansel Adams beautiful
prints of extended brightness range subjects are more the
result of manipulation in printing than from the use of Zone
System exposure although an understanding of the principals
can insure that the negative has the necessary data on it
for doing this.
BTW, I disagree with the statement (which I snipped) by
a previous poster that film has a two stop underexposure
latitude. When the speed is determined by the ISO method
there is almost no underexposure latitude since the method
is intended to find the minimum exposure that will result in
good shadow detail. One can underexpose somewhat but there
will be a loss of shadow detail. OTOH, there is an enormous
overexpsure latitude, maybe as much as ten stops for some
films.
--
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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