Archived posting to the Leica Users Group, 2000/11/05
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]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