MattKing
Moderator
You might find it interesting to read the information in Kodak's data sheet for new T-Max 400:
"EXPOSURE
The nominal speed of KODAK PROFESSIONAL T-MAX
400 Film is EI 400. It was determined in a manner
published in ISO standards. Because of its great latitude,
you can underexpose this film by one stop (at EI 800) and
still obtain high quality with normal development in most
developers. There will be no change in the grain in the final
print, but there will be a slight loss of shadow detail and a
reduction in printing contrast of about one-half paper
grade.
When you need very high speed, you can expose
T-MAX 400 Film at EI 1600 and increase the development
time. With the longer development time, there will be an
increase in contrast and graininess with additional loss of
shadow detail, but negatives will still produce good prints.
You can even expose this film at EI 3200 with a longer
development time. Underexposing by three stops and
using three-stop push-processing produces a further
increase in contrast and graininess, and additional loss of
shadow detail, but the results will be acceptable for some
applications.
The speed numbers for this film are expressed as
Exposure Indexes (EI). Use these exposure indexes with
meters or cameras marked for ISO⁄ASA or ISO⁄DIN speeds
in daylight or artificial light.
The developer you use to process this film affects the
exposure index. Set your camera or meter (marked for
ISO⁄ASA or ISO⁄DIN speeds) at the speed for your
developer given in the table.
.....
Under most conditions, youll obtain highest quality with
normal exposure at the rated exposure index and normal
development. For high-contrast scenes, youll obtain
highest quality if you increase exposure by one or two
stops and process the film normally.
* Pushing exposure results in slight losses of quality compared with normal
exposure and normal processing. You can also use other Kodak developers
for pushing this film; however, T-MAX Developer, T-MAX RS Developer and
Replenisher, and XTOL Developer produce higher-quality tone reproduction
(better shadow detail) under these conditions.
For high-contrast scenes, such as spotlighted performers under harsh
lighting, expose and process as indicated in the table. However, when detail
in the deep-shadow areas is important to the scene, increase exposure by 2
stops and process your film normally.
Pushing exposure and processing by 3 stops increases contrast and
graininess and decreases shadow detail further. Expose and process a test roll
to determine if the results are acceptable for your needs."
I repeat that excerpt to help illustrate how recommendations about exposure in circumstances different than ISO testing are based on a lot of criteria that isn't as clear cut and inflexible as the ISO testing.
Some people are amazed that Kodak does not recommend an increase in development time for T-Max 400 when it is exposed at an EI of 800. They don't because their criteria for quality is best met when the development is not increased. If the quality control people at Ilford were to apply their equally respected criteria to the same question, they might very well prefer some factors over others, and recommend something slightly different.
"EXPOSURE
The nominal speed of KODAK PROFESSIONAL T-MAX
400 Film is EI 400. It was determined in a manner
published in ISO standards. Because of its great latitude,
you can underexpose this film by one stop (at EI 800) and
still obtain high quality with normal development in most
developers. There will be no change in the grain in the final
print, but there will be a slight loss of shadow detail and a
reduction in printing contrast of about one-half paper
grade.
When you need very high speed, you can expose
T-MAX 400 Film at EI 1600 and increase the development
time. With the longer development time, there will be an
increase in contrast and graininess with additional loss of
shadow detail, but negatives will still produce good prints.
You can even expose this film at EI 3200 with a longer
development time. Underexposing by three stops and
using three-stop push-processing produces a further
increase in contrast and graininess, and additional loss of
shadow detail, but the results will be acceptable for some
applications.
The speed numbers for this film are expressed as
Exposure Indexes (EI). Use these exposure indexes with
meters or cameras marked for ISO⁄ASA or ISO⁄DIN speeds
in daylight or artificial light.
The developer you use to process this film affects the
exposure index. Set your camera or meter (marked for
ISO⁄ASA or ISO⁄DIN speeds) at the speed for your
developer given in the table.
.....
Under most conditions, youll obtain highest quality with
normal exposure at the rated exposure index and normal
development. For high-contrast scenes, youll obtain
highest quality if you increase exposure by one or two
stops and process the film normally.
* Pushing exposure results in slight losses of quality compared with normal
exposure and normal processing. You can also use other Kodak developers
for pushing this film; however, T-MAX Developer, T-MAX RS Developer and
Replenisher, and XTOL Developer produce higher-quality tone reproduction
(better shadow detail) under these conditions.
For high-contrast scenes, such as spotlighted performers under harsh
lighting, expose and process as indicated in the table. However, when detail
in the deep-shadow areas is important to the scene, increase exposure by 2
stops and process your film normally.
Pushing exposure and processing by 3 stops increases contrast and
graininess and decreases shadow detail further. Expose and process a test roll
to determine if the results are acceptable for your needs."
I repeat that excerpt to help illustrate how recommendations about exposure in circumstances different than ISO testing are based on a lot of criteria that isn't as clear cut and inflexible as the ISO testing.
Some people are amazed that Kodak does not recommend an increase in development time for T-Max 400 when it is exposed at an EI of 800. They don't because their criteria for quality is best met when the development is not increased. If the quality control people at Ilford were to apply their equally respected criteria to the same question, they might very well prefer some factors over others, and recommend something slightly different.