Improved T-Max 400

On Nov 1, 8:48 pm, Peter Irwin wrote:

Note that the inertia based Weston speed also tracked
pretty well with the Jones Kodak Speed and Old ASA.
The normal relationship would be that Weston 40
equaled Kodak 200 and Old ASA 50. Many films
seem to have fit that relationship perfectly
and I'm unaware of any that were more than
1/3 stop off.

I was wrong about this. I looked up official Weston
speeds from 1940 and compared them to Kodak speeds
from 1943 - and they just aren't always that close.
The Weston speed system was ok, but it
wasn't that good. Weston speeds quoted by Kodak
in the 1943 book are just converted Kodak speeds
- so of course those match.


Old DIN (1936)

I was also wrong about the date of the original DIN
speed standard. DIN 4512 was 1934 not 1936.

Peter.
--

On Nov 1, 8:48 pm, Peter Irwin wrote:
Richard Knoppow wrote:

This is getting long but I can't find anything to snip.

I hope that means that it was mostly ok.

I don't know when Kodak began using Jones' method
internally but it did begin to publish Kodak speeds around
1939. Jones actually worked out his system much earlier.

I'm sure that's right, but published Kodak speeds
from before 1939 are a different system. The Kodak
speeds listed in the 1938 edition of "Eastman
Professional Films" are not the Jones system.
The pre-1939 Kodak system was based on inertia
(Like Weston and H&D) and is equal to ten times
the Weston speed.

The ASA adopted the system in 1943 with a
safety factor of 2.

That's what you've said several times.

But - In "Kodak Films" fifth edition 1951
from the Kodak Reference Handbook on page 16,
it says "For the black-and-white continuous
tone negative materials covered by the standard,
a safety factor of 2.5 is used."

In "Kodak Films" seventh edition 1956, it says
the same thing on the top of page 21.

ASA speeds were 1/4 of Kodak speeds. The resulting
number could be used with either Weston or General Electric
meters of the time with insignificant error. However, the
safety factor increased the exposure by a stop over the
Jones speed point. A film rated Kodak 400 would be an ASA
100 film by this standard. In its data sheets of this time
Kodak stated that the exposure could be reduced a stop if
work was carried out carefully.

That's true, but I expect you have the same booklets
I have where it says the safety factor is 2.5.

The second ASA standard changed the method of
measurement from the Jones minimum usable gradient to a
fixed minimum density method as adopted by the DIN in the
early 1950's (don't have the exact date at hand).

The 1958 Ilford Manual by Horder has the date for
revised DIN standard as 1957 (p. 284, 287).
The older 1936 DIN system used the same minimum
density requirement, but specified development
for maximum speed, rather than a standard
development representing something like
normal use - as was used from 1957.

I think the ASA Standard is ANSI PH2.5-1960, at least
it is cited that way in Photographic Sensitometry
by Todd and Zakia (1974 p.164).

These would just be publication dates, the actual
work would always be a bit earlier.

However, they wanted to accomplish two things:
first was to make the speeds compatible with
earlier ASA speeds,

That made a lot of sense given the number
of meters already in use.

and secondly, to maintain something like the
Jones idea of the minimum gradient.

It doesn't use the 0.3 times average gradient
criterion though, it uses the 0.1 density
above base + fog criterion.

The ASA conducted extensive surveys of films of
the time and found that there was a nearly constant
ratio between the fixed minimum density, that is
log 0.1 above fog plus support density, and the
Jones point as found using the Jones method.

It seems to hold good within a third of a stop
based on the ratings of films just before
and just after the change.

Note that the inertia based Weston speed also tracked
pretty well with the Jones Kodak Speed and Old ASA.
The normal relationship would be that Weston 40
equaled Kodak 200 and Old ASA 50. Many films
seem to have fit that relationship perfectly
and I'm unaware of any that were more than
1/3 stop off.

The key seems to be normal development.
Weston, Old ASA, and ISO (New ASA/New DIN)
use different criteria, but track quite well.
They all use normal development.

Old DIN (1936) tracked the other systems very badly.
It used development for maximum speed.
The same criterion, but with normal development,
works very well.

This obviated the difficult Jones measurement.
The ratio turned out to be about 1.25 times
the exposure required to reach the DIN density point.

The math in my previous post showed that
an ISO 400/27 film has a DIN density
point at -2.7 log lux seconds and that
an Old ASA 200 film had a Jones Point
at -2.9. Unless someone shows that
my formulas or math are wrong, I'm
sticking to those figures.

The Jones Point for a typical film
is thus 0.2 log units to the left
and represents 2/3 of a stop less exposure
than the DIN point.

So, a factor of 0.8, the reciprocal of 1.25
is introduced into the calculation of the speed
in the new ASA method.

That was to get the numbers they wanted,
but the actual difference between the DIN
point and the Jones point for films
where New ASA is double Old ASA is 0.2 log units,
2/3 of a stop or a factor of around 1.6.

In effect the speeds were now double those measured
by the old ASA method and half of the Kodak speed.

True for most films.

I reiterate that the factor in the current speed method
is NOT a safety factor but rather to bring measurements made
by the method into agreement with the speed that would be
measured by the Jones/Kodak method and reverts to Jones'
original idea of finding the minimum exposure that results
in good tone rendition.

Yes but if the "Kodak Films" booklets are correct
that Old ASA had a safety factor of 2.5, then the
doubling of the speed ratings should have reduced
this to 1.25. I agree that this has nothing to
do with the 0.8 in the formula. The 0.8 in the
formula just puts the scale where they wanted it.

The original Kodak method does not seem to have had a
fixed contrast, however, contrast does affect the speeds
measured by either method. The Kodak method does specify a
fixed exposure interval, much the same as the current
method.

Yes, but changes in development time tend to affect
the contrast in the toe and the overall contrast
at the same time. Since the Jones method depends
on the ratio between the slope of the curve
at the Jones point and the overall slope, changes
in development will have less effect on the
Jones point than on the DIN point.

Since the old ASA method and the new ISO method are
compatible as to speed point even though measured by
different techniques, its possible to translate old ASA (pre
1958) speeds to equivalent modern speeds by simply
multiplying by 2. Keep in mind that the speeds in both
systems are rounded off as were old Weston speeds so there
may not be an exact agreement. Also, even though Kodak used
the same trade names for decades the emulsions were changed
many times. Current Plus-X is not the same as the product
of, say, 1948 although its broad speed category is about the
same and its intended use is about the same so speed
comparisons must be made with some care.

Plus-X 35mm did vary in rated speed over the years.

Kodak 200 in 1943 (Old ASA 50)
ASA 50 in 1951
ASA 80 in 1956

But the speed of both Plus-X 35mm and Verichrome
Pan just before the change was ASA 80 and both
were ASA 125 just after the change and forever after.
I'm aware that both systems round to the nearest
1/3 stop so that a 1/3 stop difference in reality
may be hardly anything at all.

My impression is that Plus-X 35mm, while now
greatly improved from the film introduced in 1938,
never underwent any rapid obvious change from
year to year. Every now and then the new stuff
would be just a little better. A bunch of minor
changes over 69 years can add up a lot.

Then again, it was always around 100 speed
by today's standards. It was always a double
coated film, always type B panchromatic,
always had a high acutance, and was always
fine grained for its time.

What is surprizing is how fast films of the mid 1940's
were. The difference was, of course, grain. A 1940's film
which would measure 400 on the ISO system would be extremely
grainy compared to a modern film of that speed.

Medium speed films were actually pretty ok.
I have some of my father's Verichrome negatives
that he took with his Brownie in the 1940s.
Even with department store processing, the
negatives are still a bit finer grained
than today's Tri-X in D-76 1:1.

Peter.
--


Everything I have ever read says the safety factor before 1959 was
2.5. It was reduced to 1.25 in the new system. The right factor is
about 1.75.

"UC" wrote in message
ups.com...
On Nov 1, 8:48 pm, Peter Irwin wrote:
Richard Knoppow wrote:

This is getting long but I can't find anything to snip.

I hope that means that it was mostly ok.

I don't know when Kodak began using Jones' method
internally but it did begin to publish Kodak speeds
around
1939. Jones actually worked out his system much earlier.

I'm sure that's right, but published Kodak speeds
from before 1939 are a different system. The Kodak
speeds listed in the 1938 edition of "Eastman
Professional Films" are not the Jones system.
The pre-1939 Kodak system was based on inertia
(Like Weston and H&D) and is equal to ten times
the Weston speed.

The ASA adopted the system in 1943 with a
safety factor of 2.

That's what you've said several times.

But - In "Kodak Films" fifth edition 1951
from the Kodak Reference Handbook on page 16,
it says "For the black-and-white continuous
tone negative materials covered by the standard,
a safety factor of 2.5 is used."

In "Kodak Films" seventh edition 1956, it says
the same thing on the top of page 21.

ASA speeds were 1/4 of Kodak speeds. The resulting
number could be used with either Weston or General
Electric
meters of the time with insignificant error. However,
the
safety factor increased the exposure by a stop over the
Jones speed point. A film rated Kodak 400 would be an
ASA
100 film by this standard. In its data sheets of this
time
Kodak stated that the exposure could be reduced a stop
if
work was carried out carefully.

That's true, but I expect you have the same booklets
I have where it says the safety factor is 2.5.

The second ASA standard changed the method of
measurement from the Jones minimum usable gradient to a
fixed minimum density method as adopted by the DIN in
the
early 1950's (don't have the exact date at hand).

The 1958 Ilford Manual by Horder has the date for
revised DIN standard as 1957 (p. 284, 287).
The older 1936 DIN system used the same minimum
density requirement, but specified development
for maximum speed, rather than a standard
development representing something like
normal use - as was used from 1957.

I think the ASA Standard is ANSI PH2.5-1960, at least
it is cited that way in Photographic Sensitometry
by Todd and Zakia (1974 p.164).

These would just be publication dates, the actual
work would always be a bit earlier.

However, they wanted to accomplish two things:
first was to make the speeds compatible with
earlier ASA speeds,

That made a lot of sense given the number
of meters already in use.

and secondly, to maintain something like the
Jones idea of the minimum gradient.

It doesn't use the 0.3 times average gradient
criterion though, it uses the 0.1 density
above base + fog criterion.

The ASA conducted extensive surveys of films of
the time and found that there was a nearly constant
ratio between the fixed minimum density, that is
log 0.1 above fog plus support density, and the
Jones point as found using the Jones method.

It seems to hold good within a third of a stop
based on the ratings of films just before
and just after the change.

Note that the inertia based Weston speed also tracked
pretty well with the Jones Kodak Speed and Old ASA.
The normal relationship would be that Weston 40
equaled Kodak 200 and Old ASA 50. Many films
seem to have fit that relationship perfectly
and I'm unaware of any that were more than
1/3 stop off.

The key seems to be normal development.
Weston, Old ASA, and ISO (New ASA/New DIN)
use different criteria, but track quite well.
They all use normal development.

Old DIN (1936) tracked the other systems very badly.
It used development for maximum speed.
The same criterion, but with normal development,
works very well.

This obviated the difficult Jones measurement.
The ratio turned out to be about 1.25 times
the exposure required to reach the DIN density point.

The math in my previous post showed that
an ISO 400/27 film has a DIN density
point at -2.7 log lux seconds and that
an Old ASA 200 film had a Jones Point
at -2.9. Unless someone shows that
my formulas or math are wrong, I'm
sticking to those figures.

The Jones Point for a typical film
is thus 0.2 log units to the left
and represents 2/3 of a stop less exposure
than the DIN point.

So, a factor of 0.8, the reciprocal of 1.25
is introduced into the calculation of the speed
in the new ASA method.

That was to get the numbers they wanted,
but the actual difference between the DIN
point and the Jones point for films
where New ASA is double Old ASA is 0.2 log units,
2/3 of a stop or a factor of around 1.6.

In effect the speeds were now double those measured
by the old ASA method and half of the Kodak speed.

True for most films.

I reiterate that the factor in the current speed
method
is NOT a safety factor but rather to bring measurements
made
by the method into agreement with the speed that would
be
measured by the Jones/Kodak method and reverts to Jones'
original idea of finding the minimum exposure that
results
in good tone rendition.

Yes but if the "Kodak Films" booklets are correct
that Old ASA had a safety factor of 2.5, then the
doubling of the speed ratings should have reduced
this to 1.25. I agree that this has nothing to
do with the 0.8 in the formula. The 0.8 in the
formula just puts the scale where they wanted it.

The original Kodak method does not seem to have had a
fixed contrast, however, contrast does affect the
speeds
measured by either method. The Kodak method does
specify a
fixed exposure interval, much the same as the current
method.

Yes, but changes in development time tend to affect
the contrast in the toe and the overall contrast
at the same time. Since the Jones method depends
on the ratio between the slope of the curve
at the Jones point and the overall slope, changes
in development will have less effect on the
Jones point than on the DIN point.

Since the old ASA method and the new ISO method are
compatible as to speed point even though measured by
different techniques, its possible to translate old ASA
(pre
1958) speeds to equivalent modern speeds by simply
multiplying by 2. Keep in mind that the speeds in both
systems are rounded off as were old Weston speeds so
there
may not be an exact agreement. Also, even though Kodak
used
the same trade names for decades the emulsions were
changed
many times. Current Plus-X is not the same as the
product
of, say, 1948 although its broad speed category is
about the
same and its intended use is about the same so speed
comparisons must be made with some care.

Plus-X 35mm did vary in rated speed over the years.

Kodak 200 in 1943 (Old ASA 50)
ASA 50 in 1951
ASA 80 in 1956

But the speed of both Plus-X 35mm and Verichrome
Pan just before the change was ASA 80 and both
were ASA 125 just after the change and forever after.
I'm aware that both systems round to the nearest
1/3 stop so that a 1/3 stop difference in reality
may be hardly anything at all.

My impression is that Plus-X 35mm, while now
greatly improved from the film introduced in 1938,
never underwent any rapid obvious change from
year to year. Every now and then the new stuff
would be just a little better. A bunch of minor
changes over 69 years can add up a lot.

Then again, it was always around 100 speed
by today's standards. It was always a double
coated film, always type B panchromatic,
always had a high acutance, and was always
fine grained for its time.

What is surprizing is how fast films of the mid 1940's
were. The difference was, of course, grain. A 1940's
film
which would measure 400 on the ISO system would be
extremely
grainy compared to a modern film of that speed.

Medium speed films were actually pretty ok.
I have some of my father's Verichrome negatives
that he took with his Brownie in the 1940s.
Even with department store processing, the
negatives are still a bit finer grained
than today's Tri-X in D-76 1:1.

Peter.
--


Everything I have ever read says the safety factor before
1959 was
2.5. It was reduced to 1.25 in the new system. The right
factor is
about 1.75.

I don't know what you mean by the "right factor" the
numbers 1.75 do not exist in the standard.
Also, the 0.8 or 1.25 factor in the new standard is
_NOT_ a safety factor as I explained in my long previous
post. It is meant to adjust the value gotten from the
straight DIN method to the speed which would result from the
Jones/Kodak minimum usable gradient method.
The ASA adoption of the Jones/Kodak method did include a
safety factor of 2.5. This was done to insure that there
would be a developable image when applied by amateurs.
Unfortunately it resulted in quite dense negatives. Jones
worked on the basis of determing the minimum practical
exposure for good tone rendition in order to obtain the best
sharpness and grain characteristic from a film. He also
found that increased exposure made little difference to the
tone rendition but that underexposure by even a small amount
resulted in poor rendition, so, the ASA and Kodak decided to
lower the film speed by about a stop to make sure people
would get acceptable results. Tone rendition was considered
more important than optimum grain and sharpness.
Again speeds _reported_ by the current method are about
double those obtained by the original ASA method and about
half of those obtained by the method used by Kodak
internally. the division of the Kodak speed by a factor of
two fits the resulting speed to the calibration of the
exposure meter calculators current in the United States in
the 1940's, i.e. Weston and General Electric. Weston had
their own system of determining speed and all measurements
were made, at least at first, by Weston, so there was no
temptation for manufacturers to cheat, as they could with
the earlier DIN, Schneiner, or H&D systems, all being used
at the time. I have never found a description of the method
used by General Electric. GE speeds were two numbers higher
than Weston speeds and the original ASA sytem was designed
to result in a number in-between these two so it could be
used on either meter with insignificant error. Weston speeds
were rounded off so that all films within a bracketed range
had the same speed value. Probably GE did the same.
Actually, the current ISO standard also has rounded off
ranges so published speeds in any of these four systems are,
and have always been, approximations.
Again, the speed depends on the degree of development.
The ISO and new DIN standard effectively specify a contrast
index by specifying the density range to be obtained from an
exposure range. Any change in the contrast will affect the
effective speed. That's why the term EI, or Exposure Index
should be used when a speed has not been determined by the
ISO method.
Also, common developers can affect speed. The range is
around 1.5 stops overall for developers ranging from
Microdol-X or Perceptol (low end of speed when used full
strength) to Xtol, T-Max, Microphen (all at the high end of
speed) with developers like D-76 being in the middle. The
standard requires that the developer used be specified with
the speed ratings. Kodak does this on its development charts
but I have never seen a developer specified on a film box.

In any case, the calculator of an exposure meter is
designed to fit an average scene into the usable range of
the film. Changing the film speed simply moves the exposure
left or right along the curve. The mid gray value, which is
often argued, is actually of little relevance, provided its
in the linear part of the curve somewhere. More important is
where shadows that are to have some detail fall. They must
be recorded on the film characteristic at a point where the
contrast is high enough to record the detail. If too far
down on the toe the shadows become blank. Moving them up
will improve their rendition but exposure must not be moved
up the curve enough to make the highlights _which are to
have detail_ fall onto the shoulder, where, again, the
contrast is low. For modern film there is no practical
shoulder unless the film is overexposed by a great many
stops.
Printing density is another consideration: overall
density becomes higher as exposure is increased. Negatives
which are so dense that they take very long printing
exposures are undesirable even if they deliver good tone
rendition.
Worrying about small errors in exposure is useless for
normal B&W, the important thing is to give the negative
enough exposure for good shadow detail. Once this mimimum is
met there is a long range of increased exposure which will
still result in good tone rendition in the print.


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

On Nov 2, 5:24 pm, "Richard Knoppow" wrote:
"UC" wrote in message

ups.com...

On Nov 1, 8:48 pm, Peter Irwin wrote:
Richard Knoppow wrote:

This is getting long but I can't find anything to snip.

I hope that means that it was mostly ok.

I don't know when Kodak began using Jones' method
internally but it did begin to publish Kodak speeds
around
1939. Jones actually worked out his system much earlier.

I'm sure that's right, but published Kodak speeds
from before 1939 are a different system. The Kodak
speeds listed in the 1938 edition of "Eastman
Professional Films" are not the Jones system.
The pre-1939 Kodak system was based on inertia
(Like Weston and H&D) and is equal to ten times
the Weston speed.

The ASA adopted the system in 1943 with a
safety factor of 2.

That's what you've said several times.

But - In "Kodak Films" fifth edition 1951
from the Kodak Reference Handbook on page 16,
it says "For the black-and-white continuous
tone negative materials covered by the standard,
a safety factor of 2.5 is used."

In "Kodak Films" seventh edition 1956, it says
the same thing on the top of page 21.

ASA speeds were 1/4 of Kodak speeds. The resulting
number could be used with either Weston or General
Electric
meters of the time with insignificant error. However,
the
safety factor increased the exposure by a stop over the
Jones speed point. A film rated Kodak 400 would be an
ASA
100 film by this standard. In its data sheets of this
time
Kodak stated that the exposure could be reduced a stop
if
work was carried out carefully.

That's true, but I expect you have the same booklets
I have where it says the safety factor is 2.5.

The second ASA standard changed the method of
measurement from the Jones minimum usable gradient to a
fixed minimum density method as adopted by the DIN in
the
early 1950's (don't have the exact date at hand).

The 1958 Ilford Manual by Horder has the date for
revised DIN standard as 1957 (p. 284, 287).
The older 1936 DIN system used the same minimum
density requirement, but specified development
for maximum speed, rather than a standard
development representing something like
normal use - as was used from 1957.

I think the ASA Standard is ANSI PH2.5-1960, at least
it is cited that way in Photographic Sensitometry
by Todd and Zakia (1974 p.164).

These would just be publication dates, the actual
work would always be a bit earlier.

However, they wanted to accomplish two things:
first was to make the speeds compatible with
earlier ASA speeds,

That made a lot of sense given the number
of meters already in use.

and secondly, to maintain something like the
Jones idea of the minimum gradient.

It doesn't use the 0.3 times average gradient
criterion though, it uses the 0.1 density
above base + fog criterion.

The ASA conducted extensive surveys of films of
the time and found that there was a nearly constant
ratio between the fixed minimum density, that is
log 0.1 above fog plus support density, and the
Jones point as found using the Jones method.

It seems to hold good within a third of a stop
based on the ratings of films just before
and just after the change.

Note that the inertia based Weston speed also tracked
pretty well with the Jones Kodak Speed and Old ASA.
The normal relationship would be that Weston 40
equaled Kodak 200 and Old ASA 50. Many films
seem to have fit that relationship perfectly
and I'm unaware of any that were more than
1/3 stop off.

The key seems to be normal development.
Weston, Old ASA, and ISO (New ASA/New DIN)
use different criteria, but track quite well.
They all use normal development.

Old DIN (1936) tracked the other systems very badly.
It used development for maximum speed.
The same criterion, but with normal development,
works very well.

This obviated the difficult Jones measurement.
The ratio turned out to be about 1.25 times
the exposure required to reach the DIN density point.

The math in my previous post showed that
an ISO 400/27 film has a DIN density
point at -2.7 log lux seconds and that
an Old ASA 200 film had a Jones Point
at -2.9. Unless someone shows that
my formulas or math are wrong, I'm
sticking to those figures.

The Jones Point for a typical film
is thus 0.2 log units to the left
and represents 2/3 of a stop less exposure
than the DIN point.

So, a factor of 0.8, the reciprocal of 1.25
is introduced into the calculation of the speed
in the new ASA method.

That was to get the numbers they wanted,
but the actual difference between the DIN
point and the Jones point for films
where New ASA is double Old ASA is 0.2 log units,
2/3 of a stop or a factor of around 1.6.

In effect the speeds were now double those measured
by the old ASA method and half of the Kodak speed.

True for most films.

I reiterate that the factor in the current speed
method
is NOT a safety factor but rather to bring measurements
made
by the method into agreement with the speed that would
be
measured by the Jones/Kodak method and reverts to Jones'
original idea of finding the minimum exposure that
results
in good tone rendition.

Yes but if the "Kodak Films" booklets are correct
that Old ASA had a safety factor of 2.5, then the
doubling of the speed ratings should have reduced
this to 1.25. I agree that this has nothing to
do with the 0.8 in the formula. The 0.8 in the
formula just puts the scale where they wanted it.

The original Kodak method does not seem to have had a
fixed contrast, however, contrast does affect the
speeds
measured by either method. The Kodak method does
specify a
fixed exposure interval, much the same as the current
method.

Yes, but changes in development time tend to affect
the contrast in the toe and the overall contrast
at the same time. Since the Jones method depends
on the ratio between the slope of the curve
at the Jones point and the overall slope, changes
in development will have less effect on the
Jones point than on the DIN point.

Since the old ASA method and the new ISO method are
compatible as to speed point even though measured by
different techniques, its possible to translate old ASA
(pre
1958) speeds to equivalent modern speeds by simply
multiplying by 2. Keep in mind that the speeds in both
systems are rounded off as were old Weston speeds so
there
may not be an exact agreement. Also, even though Kodak
used
the same trade names for decades the emulsions were
changed
many times. Current Plus-X is not the same as the
product
of, say, 1948 although its broad speed category is
about the
same and its intended use is about the same so speed
comparisons must be made with some care.

Plus-X 35mm did vary in rated speed over the years.

Kodak 200 in 1943 (Old ASA 50)
ASA 50 in 1951
ASA 80 in 1956

But the speed of both Plus-X 35mm and Verichrome
Pan just before the change was ASA 80 and both
were ASA 125 just after the change and forever after.
I'm aware that both systems round to the nearest
1/3 stop so that a 1/3 stop difference in reality
may be hardly anything at all.

My impression is that Plus-X 35mm, while now
greatly improved from the film introduced in 1938,
never underwent any rapid obvious change from
year to year. Every now and then the new stuff
would be just a little better. A bunch of minor
changes over 69 years can add up a lot.

Then again, it was always around 100 speed
by today's standards. It was always a double
coated film, always type B panchromatic,
always had a high acutance, and was always
fine grained for its time.

What is surprizing is how fast films of the mid 1940's
were. The difference was, of course, grain. A 1940's
film
which would measure 400 on the ISO system would be
extremely
grainy compared to a modern film of that speed.

Medium speed films were actually pretty ok.
I have some of my father's Verichrome negatives
that he took with his Brownie in the 1940s.
Even with department store processing, the
negatives are still a bit finer grained
than today's Tri-X in D-76 1:1.

Peter.
--


Everything I have ever read says the safety factor before
1959 was
2.5. It was reduced to 1.25 in the new system. The right
factor is
about 1.75.

I don't know what you mean by the "right factor" the
numbers 1.75 do not exist in the standard.
Also, the 0.8 or 1.25 factor in the new standard is
_NOT_ a safety factor as I explained in my long previous
post. It is meant to adjust the value gotten from the
straight DIN method to the speed which would result from the
Jones/Kodak minimum usable gradient method.
The ASA adoption of the Jones/Kodak method did include a
safety factor of 2.5. This was done to insure that there
would be a developable image when applied by amateurs.
Unfortunately it resulted in quite dense negatives. Jones
worked on the basis of determing the minimum practical
exposure for good tone rendition in order to obtain the best
sharpness and grain characteristic from a film. He also
found that increased exposure made little difference to the
tone rendition but that underexposure by even a small amount
resulted in poor rendition, so, the ...

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The 'new' standard reduced the safety factor, but did not eliminate
it. It was reduced from 2.5 to 1.25. I have read this somewhere. A
factor of 1.75 (basically, lowering the speeds by 1/2 stop) would put
the shadows up a little higher on the curve and give better separation
of shadow detail.

Richard Knoppow wrote:

The ASA adoption of the Jones/Kodak method did include a
safety factor of 2.5. This was done to insure that there
would be a developable image when applied by amateurs.

It also tended to match what the Weston and GE systems
were already doing. The Weston and GE systems were
actually working quite well in practice. The change
to a unified system with a really sound theoretical basis
was obviously a good thing, but it was probably desirable
at the time for the new system to give people answers
which were close to what they were already getting
from their meters.

Even in the 1943 Kodak datasheets, there was a sentence
"When it is desired to reduce the exposure to a
minimum, these meter settings can be doubled with
little danger of of serious underexposure."

Unfortunately it resulted in quite dense negatives.

My understanding is that a one stop increase
in exposure typically results in an increased
negative density of 0.2 or so. This seems to
me to be a fairly small shift. Doubling
the exposure time for the negative will less
than double the exposure time for the print.

Jones worked on the basis of determining the minimum
practical exposure for good tone rendition in order
to obtain the best sharpness and grain characteristic
from a film. He also found that increased exposure made
little difference to the tone rendition but that
underexposure by even a small amount resulted in poor
rendition, so, the ASA and Kodak decided to lower the
film speed by about a stop to make sure people
would get acceptable results. Tone rendition was
considered more important than optimum grain and sharpness.

Even then, the increased grain and loss of sharpness
from 1 stop or so extra exposure must have been
quite small.

According to T.L.J. Bentley's "Manual of the Miniature
Camera" (4th ed. 1953 page 102) - "The resolution
obtainable with photographic film suffers to some extent
with excessive exposure, but with a good film the effect is
not so noticeable in practice as some statements suggest:
it can be shown by test that, at X 16 enlargement under
critical conditions, the deterioration with an increase
in exposure to eight times the least exposure giving an
enlargement of optimum quality is barely detectable
under the closest scrutiny."

Even if you think you might be somewhat fussier,
it doesn't seem that the adverse effects of a single stop
increase could have been very noticeable even in 1953.

Again speeds reported by the current method are about
double those obtained by the original ASA method and about
half of those obtained by the method used by Kodak
internally. the division of the Kodak speed by a factor of
two fits the resulting speed to the calibration of the
exposure meter calculators current in the United States in
the 1940's, i.e. Weston and General Electric. Weston had
their own system of determining speed and all measurements
were made, at least at first, by Weston, so there was no
temptation for manufacturers to cheat, as they could with
the earlier DIN, Schneiner, or H&D systems, all being used
at the time.

In the early 20th century, Alfred Watkins produced
lists of measured speeds for plates sold in the UK.
In theory his numbers should have been 1.47 times
higher than honest H&D speeds, but in practice they
are generally lower than manufacturers' rated speeds.
When I last had a look at this it appeared to me
that Ilford H&D used a fudge factor of two. This
appears to have remained the case from the early teens
through the 1940s. Ilford H&D can be converted to Weston
by dividing by 50, and roughly to modern ISO speeds
by dividing by 20.

Ilford seems to have been quite open about this:
in the 1934 Ilford Manual on page 40, it reads
"It might be mentioned, further, that for various
reasons the original details laid down by Hurter
& Driffield have been departed from to some extent,
and in consequence the H&D speed number of an emulsion,
though correctly only about two-thirds that of a
Watkins number, is generally given as about one-third
higher."

European Scheiner inflation seems to have been
a major problem. The DIN standard was supposed
to correct this. DIN numbers were originally
around 10 less than the Scheiner speeds, though
the difference seems to have grown to 11-13 by
the 1950s.


I have never found a description of the method
used by General Electric.

I've never seen one either. There is a good
discussion of the Weston method in the
1958 Ilford Manual.


GE speeds were two numbers higher
than Weston speeds and the original ASA sytem was designed
to result in a number in-between these two so it could be
used on either meter with insignificant error. Weston speeds
were rounded off so that all films within a bracketed range
had the same speed value. Probably GE did the same.
Actually, the current ISO standard also has rounded off
ranges so published speeds in any of these four systems are,
and have always been, approximations.

Again, the speed depends on the degree of development.
The ISO and new DIN standard effectively specify a contrast
index by specifying the density range to be obtained from an
exposure range. Any change in the contrast will affect the
effective speed. That's why the term EI, or Exposure Index
should be used when a speed has not been determined by the
ISO method.

Also, common developers can affect speed. The range is
around 1.5 stops overall for developers ranging from
Microdol-X or Perceptol (low end of speed when used full
strength) to Xtol, T-Max, Microphen (all at the high end of
speed) with developers like D-76 being in the middle.

According to a post by David Carper of Ilford
on photo.net:
http://photo.net/bboard/q-and-a-fetch-msg?msg_id=003WI4

Ilford HP5+ has an ISO speed of 500/28 in Microphen,
compared to a speed of 400/27 in ID11. The speed at
a Gbar of 0.75 is less than a third of a stop higher
than it is at a Gbar of 0.62. The speed at a Gbar of 0.55
is less than 1/4 of a stop slower than at a Gbar of 0.62.

So while changing development does change the speed point,
it doesn't appear to change it by all that much in most cases.

Printing density is another consideration: overall
density becomes higher as exposure is increased. Negatives
which are so dense that they take very long printing
exposures are undesirable even if they deliver good tone
rendition.

A single extra stop isn't going to cause any trouble
in the darkroom. An exposure of six stops over
does cause a big problem: not only are the printing
times too long - it can be hard to focus the
enlarger. A six stop overexposed negative will
actually print ok, but it is an absolutely ridiculous
thing to do except as a test to prove a point.

Peter.
--

On Nov 5, 8:32 pm, Peter Irwin wrote:

Peter has made some excellent points, and my experience corresponds
precisely with what he says. One stop increase in exposure above the
bare minimum results in hardly any change except increased shadow
detail. I use about 2/3 stop over the ISO exposure, i.e., I rate most
ISO 400 films at 250.

"Richard Knoppow" wrote in message
...

[... snip generous article ...]
the division of the Kodak speed by a factor of two fits the resulting
speed to the calibration of the exposure meter calculators current in the
United States in the 1940's, i.e. Weston and General Electric.

At one point Weston changed the calibration or setting of the dial. Was it
when ASA was introduced? Darned. I will get the big box of old Westons and
compare and let you know what I find.

In article , "pico" pico.pico.net
wrote:

"UC" wrote in message
ups.com...

Here is the curve for TMY:

http://www.kodak.com/global/en/profe...4016/f002_0507
ac.gif

Here is the curve for Tri-X Pan:

http://www.kodak.com/global/en/profe...4017/f009_0490
ac.gif

Do you see the difference?

What part of that line/curve is actually useful for making photographs? You
never use the so-called shoulder - it is outside the useful exposure range.

Film: You can use all of a curve that fits between .001 and 1.71
Ha ha less image area from .001 to .15 & the 1.00 to 1.71 areas!

Paper: You must compress all film values to fit a range between .15 and
2.00 for a natural and real representation

--
Reality is a picture perfected and never looking back.