[Leica] APX25 replacement

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

Is there life after APX25? A scientifically conducted study by several
German authors in 1990 gave these results. Technical Pan had a resolving
power of 250 lines per mm and APX25 of 180 lines per mm. These were the
best. A step below these two were almost on equal footing: PanFPlus and
Tmax100, with a small finegrain edge for PanF. These data in another
notation. TP and APX could resolve details of a width of  4 to 5 micron.
That is the maximum definition for a lens like the Apo-Summicron-R 2/180,
which defines the practical upper limit for the moment. The recently
designed  Leica lenses however will be slightly below this level (in the
region of 7 to 10 micron), where the PFP and TMX are located. Older Leica
lenses have a limit at 20 micron generally speaking.
My own comparisons (prints at 20x and microscope analysis at 100 and 400
times enlargement) do indeed show a theoretical advantage of the TP and
APX25 emulsion.(Both however are challenged by the new BW film, I am
currently investigating).
For most situations, the PFP would be a worthy replacement of the APX25 with
the additional plus of a full stop more speed and it is a true speed of
ISO50. Because the APX25 has a fairly steep curve, the sharpness impression
is excellent. The PFP however has a moderately steep curve, giving a
smoother graded tonality.
The sharpness impression is a bit less, but even so an enlarger lens like
the Apo-Rodagon-N 2.8/50 would have to perform at its best to get this level
of detail on the print at 20x enlargement.
You could try to do a comparison shooting with some of your APX25 films and
the PFP to see where the differences are and how important they are.
For most of my purposes I can easily switch between APX25 and PFP. If the
problem is demanding I have TP with CC40 filter to compensate for the
enhanced red sensitivity.

Erwin