[pure-silver] Re: Condenser envy
- From: İbrahim Pamuk <ibrahim.pamuk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Fri, 11 Apr 2008 01:06:00 +0300
Hi Richard,
Your answer was very informative and help me to understand lot. Thank you very
much
Ibrahim Pamuk
-----Original Message-----
From: pure-silver-bounce@xxxxxxxxxxxxx
[mailto:pure-silver-bounce@xxxxxxxxxxxxx] On Behalf Of Richard Knoppow
Sent: 10 Nisan 2008 Perşembe 12:32
To: pure-silver@xxxxxxxxxxxxx
Subject: [pure-silver] Re: Condenser envy
----- Original Message -----
From: "Ibrahim Pamuk" <ibrahim.pamuk@xxxxxxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Wednesday, April 09, 2008 11:46 PM
Subject: [pure-silver] Re: Condenser envy
Hi,
I understand that Callier effect results as contrast
increase. Is it possible to get higher contast due to same
approach printing with f/2.8 vs f/22?
Regards
Ibrahim Pamuk
Callier effect takes place before the light reaches the
projecting lens. The particles of silver that make up the
image scatter some of the light that strikes them. When the
light comes from one direction, as it does when a point
source or condenser type lamp is used, the scattered light
is mostly reflected away from the path to the lens so the
density looks greater. When a diffuse source is used the
light comes from a wide angle so some of the light being
scattered by the particles is reflected away from the path
to the lens as above but some of the light is scattered
_toward_ the lens, thus increasing the amount of light in
the dark areas and lowering the contrast. Since the light
rays that make up the image are those directed at the lens
the f/stop will have little, if any, effect on the contrast
other than optical effects in the lens itself and those
don't vary with Callier effect.
Again, Callier effect varies with the size of the
particles making up the image. The larger the particles the
greater the effect. For modern B&W films with silver images
the difference between coarse and fine grain films is
negligible especially as the emulsions are three dimentional
but for color films the effect is in total negligible
because the image is made up of very small dye particles
which are partially trasparent and don't scatter much light
anyway.
The usual condenser enlarging head uses a large,
diffuse, lamp so the light is partially diffuse. The light
focused on the enlarging lens is not completely collimated
(i.e., is not coming from a single direction) but is,
rather, partially diffuse due to the size and surface of the
lamp. So, the Callier effect is such as to increase contrast
for silver images somewhat but far from as much as would be
the case for either a point source at a distance or a
collimated point source. Typical partially diffusing
sources, such as those found on Omega and Bessler enlargers
is about one paper grade, maybe not even that much. The old
Elwood enlarger has a reflector and looks superficially like
a diffusion source but is actually similar to the condenser
sources above. It uses a very large diffuse lamp in an
eliptical reflector with a diffusion light equalizer above
the film which acts something like a center filter to reduce
the hot-spot at the center. The other glass plates in the
thing are plain and are used for heat absorption since the
Elwood has a reputation for cooking negatives.
Most color heads use an integrator box made of highly
diffusing reflecting surfaces and are essentially diffusion
sources, but again, for color work the image contrast is not
much affected by the type of lamphouse although the contrast
of blemishes are.
Tests made many years ago show no difference in
resolution or edge contrast (acutance) between prints made
on diffusion vs: condenser enlargers although there may be
an increase when a true point source is used.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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