another question re film grain

I've recently started using b/wfilm again.
More specifically, delta400 and xp2.
Last time I used b/w was 25 years ago,
so my memory of it is nothing but foggy!
I'm currently scannning the film with a 9000ED.

One thing I've noticed: the grain in both of these
films seems to be proportional to the exposu
in dark sections or just plain underexposed, the grain
is quite visible. In light areas or slightly overexposed
images, it reduces significantly.

Is there a rule/guideline/theory for this?
Somewhere I can read about it?

TIA for any ideas.

"Noons" wrote in message
ups.com...
I've recently started using b/wfilm again.
More specifically, delta400 and xp2.
Last time I used b/w was 25 years ago,
so my memory of it is nothing but foggy!
I'm currently scannning the film with a 9000ED.

One thing I've noticed: the grain in both of these
films seems to be proportional to the exposu
in dark sections or just plain underexposed, the grain
is quite visible. In light areas or slightly overexposed
images, it reduces significantly.

Is there a rule/guideline/theory for this?
Somewhere I can read about it?

TIA for any ideas.


Graininess, that is the appearance of grain, depends on
many things. The actual silver or dye particals which make
up the image are microscopic. In emulsion research they are
usually examined wtih an electron microscope although a high
power optical microscope will resolve them. What is seen as
grain is the "clumping" of grains at various levels in the
emulsion. Since the distribution of grains is random the
effect is to combine into larger groups of grains which are
also random. On prints the grain is actually from clear
areas in the negative where the grain clumps allow light to
pass.
Graininess does vary with density. Usually visual
graininess is minimum at medium density and is more
noticable at low and high density. This may be what you are
seeing. Also, if you are getting grain on scanned negatives
but don't seen it visually it may be a sort of aliasing due
to a complex interference pattern between the grain and the
scanning pattern of the scanner.
Note that some think that dye image films, whether color
of monochrome, have no grain. In fact they have the grain of
the silver image which generated the dye in development.
However, because the dye is in very small particals and
forms in "clouds" around the original silver, it may be less
noticable. This applies to the XP-2 which is a "chromogenic"
film, that is, the image is composed of dye particals rather
than metallic silver.
Grain and graniness (percieved grain) has been
researched pretty thoroughly and articles can be found in
some of the older textbooks on photography. Kodak also had a
booklet on grain and graininess which may still be on their
web site. While this applies to color films it may still be
helpful. Search for E-58.
As a rule, at least for B&W silver image films, exposure
should be minimised to that which will result in adequate
shadow detail. This tends to minimise grain and maximise
sharpness. For formats larger than 35mm, where minimum grain
and good avoiding image spread is less important somewhat
more exposure may result in better tone rendition.
The ISO speeds for B&W still negative film reflect the
minimum exposure for good shadow detail. Color films and
other types of films are measured using a different standard
aimed for most films at best tone rendition.


--
---
Richard Knoppow
Los Angeles, CA, USA

"Richard Knoppow" wrote in message
ink.net...

"Noons" wrote in message
ups.com...
I've recently started using b/wfilm again.
More specifically, delta400 and xp2.
Last time I used b/w was 25 years ago,
so my memory of it is nothing but foggy!
I'm currently scannning the film with a 9000ED.

One thing I've noticed: the grain in both of these
films seems to be proportional to the exposu
in dark sections or just plain underexposed, the grain
is quite visible. In light areas or slightly overexposed
images, it reduces significantly.

Is there a rule/guideline/theory for this?
Somewhere I can read about it?

TIA for any ideas.


Graininess, that is the appearance of grain, depends on
many things. The actual silver or dye particals which make
up the image are microscopic. In emulsion research they
are usually examined wtih an electron microscope although
a high power optical microscope will resolve them. What is
seen as grain is the "clumping" of grains at various
levels in the emulsion. Since the distribution of grains
is random the effect is to combine into larger groups of
grains which are also random. On prints the grain is
actually from clear areas in the negative where the grain
clumps allow light to pass.
Graininess does vary with density. Usually visual
graininess is minimum at medium density and is more
noticable at low and high density. This may be what you
are seeing. Also, if you are getting grain on scanned
negatives but don't seen it visually it may be a sort of
aliasing due to a complex interference pattern between the
grain and the scanning pattern of the scanner.
Note that some think that dye image films, whether
color of monochrome, have no grain. In fact they have the
grain of the silver image which generated the dye in
development. However, because the dye is in very small
particals and forms in "clouds" around the original
silver, it may be less noticable. This applies to the XP-2
which is a "chromogenic" film, that is, the image is
composed of dye particals rather than metallic silver.
Grain and graniness (percieved grain) has been
researched pretty thoroughly and articles can be found in
some of the older textbooks on photography. Kodak also had
a booklet on grain and graininess which may still be on
their web site. While this applies to color films it may
still be helpful. Search for E-58.
As a rule, at least for B&W silver image films,
exposure should be minimised to that which will result in
adequate shadow detail. This tends to minimise grain and
maximise sharpness. For formats larger than 35mm, where
minimum grain and good avoiding image spread is less
important somewhat more exposure may result in better tone
rendition.
The ISO speeds for B&W still negative film reflect the
minimum exposure for good shadow detail. Color films and
other types of films are measured using a different
standard aimed for most films at best tone rendition.


--
---
Richard Knoppow
Los Angeles, CA, USA


There are a couple of points I left out:-( One is that
the size of the silver grains varies with the speed of the
grain. Although emulsion making technology over the years
has resulted in much finer grain for a given speed its still
true that faster emulsions are grainier than slower ones and
that the faster halide grains in the emulsion result in
larger silver grains. This tends to work against the idea
that the dense areas have more grain because that is where
the silver from the least sensitive halide grains is
concentrated. However, again, visible grain is not from the
silver itself but from statistical groups of grains.
Another point I should make is that I refered to grain
"clumping" from statistical distribution of grains in the
emulsion, this is correct but there is another kind of
clumping. This is actual physical clumping due to migration
of silver particals toward each other in emulsions that have
been softened. This is one reason highly alkaline developer
like Rodinal tend to produce larger grain than lower pH
developers like D-76. The effect is much less pronounced in
modern films because they have very hard emulsions that do
not swell much in processing. The other kind of clumping is
due to the distribution of grains in the emulsion and is not
affected by swelling or developer pH.


--
---
Richard Knoppow
Los Angeles, CA, USA

Richard Knoppow wrote:
big snip...
not swell much in processing. The other kind of clumping is
due to the distribution of grains in the emulsion and is not
affected by swelling or developer pH.



Thank a zillion, Richard. That answered all my questions
perfectly. I'll chase up the doco as well. Yes, I'm aware
of the scanner alias "grain" problem as well. It's
particularly noticeable with older films such as D400 with the
"hazy" emulsion side. FWIW: I've noticed it is much reduced
with newer colour neg films such as the latest from
Fuji and Kodak: these have an emulsion side that is much
less "rough" and show almost no scanner alias grain
with scanners like the 9000. The latest batches of Kodak
chromogenic BW film - BW400CN - also don't show this problem
as much as Ilford's.

When we first went hybrid at my paper, shoot film then scan
for prepress, we found that negatives that looked too thin
to print scanned well and scanned faster on our Leaf scanner
that did "normal" negatives.
darkroommike

Noons wrote:
I've recently started using b/wfilm again.
More specifically, delta400 and xp2.
Last time I used b/w was 25 years ago,
so my memory of it is nothing but foggy!
I'm currently scannning the film with a 9000ED.

One thing I've noticed: the grain in both of these
films seems to be proportional to the exposu
in dark sections or just plain underexposed, the grain
is quite visible. In light areas or slightly overexposed
images, it reduces significantly.

Is there a rule/guideline/theory for this?
Somewhere I can read about it?

TIA for any ideas.

On Jul 15, 7:09 am, Noons wrote:
I've recently started using b/wfilm again.
More specifically, delta400 and xp2.
Last time I used b/w was 25 years ago,
so my memory of it is nothing but foggy!
I'm currently scannning the film with a 9000ED.

One thing I've noticed: the grain in both of these
films seems to be proportional to the exposu
in dark sections or just plain underexposed, the grain
is quite visible. In light areas or slightly overexposed
images, it reduces significantly.

Is there a rule/guideline/theory for this?
Somewhere I can read about it?

TIA for any ideas.


Yes, in my book.

Briefly, the thinnest areas of the negative are hit by the least
light. Every emuslion contains a variety of grain sizes. The smaller
ones are the least sensitive. The largest ones are the most sensitive.
Larger ones have a statistically higher probability of being struck by
light. The lower the light intensity, the greater the proportion of
large grains that are exposed. Thus, shadows contain a higher
proportion of exposed and developed large grains than mid-tones or
highlights.