# Improved T-Max 400

Discussion in 'Darkroom Developing and Printing' started by UC, Oct 10, 2007.

1. ### Nicholas O. LindanGuest

Nicholas O. Lindan, Oct 31, 2007

2. ### picoGuest

pico, Oct 31, 2007

3. ### picoGuest

Life is short, Richard. What's two rolls in a lifetime if it settles the
question?

pico, Oct 31, 2007
4. ### UCGuest

Well, that's what I have done. I have shot several rolls of each film,
adjusting developing times to give similar overall contrast with each
film. It's expensive and time-consuming, but teh developing times
given by manufacturers are often excessive and inconsistent.

UC, Oct 31, 2007
5. ### UCGuest

When you use the film, the differences appear. I develop much less
than the longest time shown. The point is that you CAN easily see the
differences. Kodak brought out Polymax paper specifically to combat
the problem. Now that Kodak is out of the paper business, they may
have adjusted the curve of TMY to work better with other papers. After
all, Tri-X Pan does sell better. TMY is 20 years old!

UC, Oct 31, 2007
6. ### Peter IrwinGuest

I think this is getting a little confusing for me.
I will state what I understand as clearly as possible,
and you can tell me if I'm going wrong somewhere.

Kodak Speed
-----------
In 1939 Kodak introduced a new speed system based
on the results of extensive psychophysical research.
This research showed that the minimum useful exposure
Required to yield an 'excellent' print was at a point
where the gradient of the H&D curve was 0.3x times the
average gradient of the slope over a range from the
exposure point to log 1.5 above the exposure point.

Finding this point called the "Jones Point" requires
a recursive operation. One has to first guess the point
on the second try.

Kodak speed is given by the formula:

Kodak Speed = 1/E

Where E is the Jones Point in Metre-Candle-Seconds.
(Same as Lux Seconds).

If you had such a thing as a exposure meter
calibrated for Kodak speeds, there would
be no safety factor. Kodak Speed didn't catch
on because few if any people owned such meters.

OLD ASA Speed 1943
------------------

In 1943 the ASA adopted the Kodak speed system
with one important change.

The formula was now

ASA Speed = 1/(4 x E)

This was intended to give numbers usable with
both Weston and GE meters. The new ASA standard
meters were to be calibrated midway between the
old Weston and GE calibrations. With an ASA
meter, old ASA speed had a safety factor of
2.5 (1 1/3 stops).

I don't think there was a particular level
of negative contrast required by the old ASA
standard, because the Jones point remains in the
same place over a fairly wide range of development
contrasts. Development contrast is supposed
to be typical of photofinishing practice.

DIN Speed
---------
The original DIN speed system (1936) was
very unsatisfactory. Sometimes it would
even get the relative speeds of films
in the wrong order. The reason for this
was that the original DIN standard required
films to be developed for maximum speed
rather than according to normal use.
Old DIN speeds are indicated by the presence
of "/10" so 24/10 degrees DIN is an old
DIN speed.

In the 1957 DIN standard, the "optimal
development" was replaced by a rigidly
specified development more typical of
real practice. People soon noticed that
the new DIN numbers actually made sense.

New ASA Speed
-------------
Since the new DIN system was easier for
film manufacturers in practice and
actually worked pretty well, the ASA
decided to adopt a new system based on
DIN speeds. It was also decided to
abandon the rather large safety factor
and have speeds roughly twice that of
the old while keeping meter calibration
unchanged.

The 2:1 relationship is typical, but is
not exactly true of all films as the following
table shows.

Film OLD ASA NEW ASA
---- ------- -------
Plus-X 35mm 80 125
Verichrome Pan 80 125
Tri-X Pan Sheet 200 320
Tri-X Pan 35mm 200 400

ISO Speed
---------
The current ISO standards for B&W film
are essentially the same as the New DIN
and New ASA standards.

Where Hm = the 0.1 above base + fog point in lux seconds.

Arithmetic speed S = 0.8/Hm

Log speed S degrees = 1 + 10 x log10 0.8/Hm

The Log ISO is in fact the same as the
DIN speed.

DIN Speed = 10 log10 1/Hm

Because 10 log10 0.8 = -1
(at least very very nearly).

So Log ISO and DIN are both equal to
the log exposure of the 0.1 above base + fog point
divided by minus 10.

The 0.8 denominator in the arithmetic speed
makes 1 ASA equal to 1 DIN and places the
New ASA or ISO arithmetic speed where it
was wanted.

example:
Tri-X pan 400
ISO 400/27 degrees
New ASA 400
New DIN 27
OLD ASA probably still 200

0.1 above base fog point (Hm) is -2.7 log lux seconds

This is true from all formulas.

ISO Artith or New ASA = 0.8/Hm
= 0.8/10^-2.7
= 0.8/0.002
= 400

ISO Log Degrees = 1 + 10 x log10 0.8/Hm
= 1 + 10 x log10 0.8/10^-2.7
= 1 + 10 x log10 400
= 1 + 10 x 2.6
= 1 + 26
= 27

DIN Speed = 10 x log10 1/Hm
= 10 x log10 1/10^-2.7
= 10 x log10 501
= 10 x 2.7
= 27

DIN Speed of 27 means Hm is -2.7 log lux seconds.
- neat - all you have to do is divide by negative 10.

If Old ASA 200 then Jones point E = - 2.9 log lux seconds

ASA Speed = 1/(4 x E)
= 1/(4 x 10^-2.9)
= 1/(4 x 0.00126)
= 1/0.00504
= 198.41

Close enough.

Peter.

Peter Irwin, Oct 31, 2007
7. ### UCGuest

It is my opinion, and that of many others, that the 'new' ASA speed
sytem introduced in 1959 gives numbers that are too high, by about 2/3
stop.

UC, Oct 31, 2007
8. ### Peter IrwinGuest

I think the primary reason for this is that the question
you want the ISO rating to answer is a different question
from the one it was designed to answer.

The question the speed rating is designed to answer
is "what is the minimum exposure required to produce
a negative from which a print judged to be 'excellent'

The question you probably want answered may be
something like "What exposure meter setting will
consistently give negatives that are easy to print
well?"

The answer to the second question is going to generally
be a lower exposure index than the ISO standard.

Peter.

Peter Irwin, Nov 1, 2007
9. ### picoGuest

I use the film. And are you not aware that Tri-X has changed again?

pico, Nov 1, 2007
10. ### picoGuest

MOST EXCELLENT observation. Kodak set the metrics. Those are the same folks
who conducted a hugely expensive and detailed survey of average customers
(largely of automatic processing) and Kodak set their metrics to those
standards, as abysymal and utterly tasteless as they were, they still
represented the drug-store processing majority. (Imagine the Bell curve -
who wants to live on top?) Oh, and what camera did Kodak come out with in
response to that study? The wholly embarassing failure, the Disc Camera!

But to add a contemporary data point - with so many people scanning
negatives, a whole new scale must be developed (no pun). Me, I'm still
scanning prints. So shoot me already.

pico, Nov 1, 2007
11. ### Peter IrwinGuest

Thanks, but I think you misunderstand me. I didn't mean
anything sarcastic when I used "excellent" in quotes.

I just meant that the two questions:

"What is the highest EI setting I can use and still
get excellent quality prints?"

and

"What is the best all-round EI setting to use in practice?"

are different questions with different answers.
The ISO speeds for negative film provide good answers
to the first question, but not necessarily to the second.

The important detail to remember is that the ISO speeds
are intended to get you very near the minimum exposure
that will work well with negative film. The maximum
exposure is generally much higher.

The optimum setting for your purposes is something
you have to find for yourself. All film manufacturers
including Kodak actually say this.

Peter.

Peter Irwin, Nov 1, 2007
12. ### picoGuest

Of course. So shoot short rolls or sheet film and custom expose and develop.

pico, Nov 1, 2007
13. ### UCGuest

Well, I don't think the shadow contrast is as good at ISO as it is at
about 2/3 ISO. This is based on many thousands of negatives.

UC, Nov 1, 2007
14. ### UCGuest

No, it has not changed, other than 'normal' manufacturing
improvements. I got this from Kodak themselves a couple of years ago.

UC, Nov 1, 2007
15. ### UCGuest

That's not necessary or practical for 35mm users. Just set your meter
at 2/3 ISO and usually you will have near-perfect negatives.

UC, Nov 1, 2007
16. ### UCGuest

No, I don't think so.

It was "What index will produce the greatest number of correct
exposures without losing definition through overexposure on automatic
cameras".

You have to remember that the late 50s saw the introduction of
numerous compact, semi-automatic and meter-coupled 35mm cameras with
primitive meters.

The way these cameras metered resulted in overexposure errors more
often than underexposure errors, if I recall correctly. It was felt
that a reduction in exposure was warranted because of this.

UC, Nov 1, 2007
17. ### Thor Lancelot SimonGuest

Thousands of negatives with the _one film_ you've evidently decided is
an acceptable film for anyone to use. How... tremendously persuasive.

I don't suppose it might have occurred to you that you could probably get
perfectly good results with almost any film you picked up from the store
shelf if you were willing to adjust your own technique. Well, as materials
disappear from the market faster and faster over the next few years, I don't
think you're going to have much choice about it, unfortunately.

Thor Lancelot Simon, Nov 1, 2007
18. ### UCGuest

??? What are you talking about? I use lots of different films. The
point is that 2/3 ISO is better than ISO for almost every film I've
tried. The exception was Ilford Pan-F, which works well right at 50.

UC, Nov 1, 2007
19. ### Richard KnoppowGuest

This is getting long but I can't find anything to snip.
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.
The ASA adopted the system in 1943 with a safety factor
of 2. ASA speeds were 1/4 of Kodak speeds. The resulting
number could be used with either Weston or General Elecric
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.
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). However,
they wanted to accomplishe two things: first was to make the
speeds compatible with earlier ASA speeds, and secondly, to
maintain something like the Jones idea of the minimum
gradient. 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. 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. So, a factor of
0.8, the reciprocal of 1.25 is introduced into the
calculation of the speed in the new ASA method. In effect
the speeds were now double those measured by the old ASA
method and half of the Kodak speed.
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.
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.
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
many times. Current Plus-X is not the same as the product
same and its intended use is about the same so speed
comparisions must be made with some care.
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.

Richard Knoppow, Nov 1, 2007
20. ### Richard KnoppowGuest

This is simply not true. The Kodak speed method was
developed over a very long time by quite valid research all
of which has been published in peer reviewed journals. Much
of the work conducted under L.A.Jones leadership was
published in the Journal of the Franklin Institute.
There is a big difference between market surveys and
scientific investigation and you are confusing the two.
Kodak's main thrust has always been to make photography
practical and easy for amateurs, that's what George
Eastman's philosophy was and he built one of the most
successful businesses in history on it. The influence is
still there even though Kodak has moved from chemical to
electronic photography.
Actually, the ISO speeds are quite practical but many
photographers do not understand how they are supposed to be
used. The speed applies only whan the specified developer is
used and when film is developed to the same contrast index
as is used in the standard measurement. This is about the
contrast for contact printing and diffusion enlarging. If
film is devloped to a lower contrast the exposure must be
increased.
Also, Jones found that the quality of the prints changed
little once the minimum exposure was reached. Minimising the
exposure minimises the density of the negatives, which, in
genera, is better for minimising grain and maximising
sharpness, however, it is often the case that increasing
exposure a bit improves tone rendition, perhaps because of
errors in using an exposure meter.

Richard Knoppow, Nov 1, 2007