[Leica] more about film

["Erwin Puts" <imxputs@knoware.nl>]

In a wide ranging BW comparison I selected films from 25 to 125 ISO and a
score of developers from D76 at one end (fine grain solvent) and Rodinal at
the other end (acutance, grain preserving). I used (in this case) test
charts, as I wanted to compare definition, grain pattern and cut-off
frequency, that is the level of detail that cannot be resolved anymore.
The first surprise: under the microscope I could see almost the same level
of detail, when enlarging 10 or 400 (!!) times. Even at 400 times (which
would amount to a print of more than 12 meter wide, surpassing clearly
Newtons Big Nudes), quite fine detail was preserved in the grain and could
be clearly seen. To use some (relative) figures. The testpattern has a
number of 25 and half of that resolution would be 12.5. Intermediate steps
are 20 and 16, meaning a reduction of 25% per step.   At enlargement 10 the
25-pattern could be seen very clearly and at 400 times the grain of course
would kill this level of resolution, but still 16 could be just detected.
Now imagine a digital camera that without alteration can produce prints of
A4 format and 12 meters wide?
The influence of the developer is relatively modest. With the same film and
same enlargement, the best could do '25'and the worst could do '16. For
critical work this may be important, but for general work it is of lesser
importance.
Film choice gave remarkable results. The 25 and 50 ISO films (exception TP
and the mystery film) could hardly resolve more details than the 100ISO
class, '34' could be seen, but '40' not. Here the limit is the lens, not the
film! So while the '25' could resolve 30% more than the 100ISO, we are
talking about a level that is hardly attainable in practice.
The two best ISO100 films are D100 and TMX in that order. D100 resolved 25%
more than TMX (same developer of course), and had more pronounced grain, but
also more edge contrast. The worst D100 combination was below the level of
the best TMX combination of course. This shows how close the performance is
nowadays.
'The most important factor that lowered resolution is camera shake, which
can influence the resolution by more than 100%, so in fact much more than
the influence of film and/or developer.
So the trend in the industry to neglect the 25ISO film for 35mm work is
understandable, as the very high performance of the best ISO100 film would
exceed the performance of most lenses and even at enlargements of 100 times
(print size almost 4 meter wide) everything the lens has been able to record
on the film can be seen and printed. This is a remarkable achievement of
current silverbased emulsions and given this level of quality the optical
industry has to come up with some tricks to push film to its limits. Only a
lens like the Apo-Telyt 4/250 would be able to exploit all what silver has
to offer.
The best allround combination? D100 and FX39 or Xtol, but good ald D76 is
very close. Even Rodinal gives amazing performance with this film.
At a level down in the definition of very fine detail, the relative number
'12,5' or '10', I have to say that almost every film in the ISO100/125 class
can handle this,  APX100, and PlusX too. With good clarity of details and
very fine performance.
More to follow

Erwin