Results: correlation of parameters

The parameters resolution, edge sharpness, development halo and granularity are influenced by film and developer in different ways and are partly interdependent. The following illustrations attempt to identify characteristic properties of the developers examined.

Figure 1 shows the parameter pair resolution / edge definition for the developers and films examined in six diagrams. The edge definition parameter varies between 0 and 1, with a maximum value of 1 corresponding to optimal edge definition.

Fig. 1 : parameter pairs for resolution and edge sharpness

Discussion:

  • FX39, D76 and SD2525 show a very pronounced (positive) correlation between resolution and sharpness, with high sharpness going hand in hand with high resolution. The ‘ranking’ is as expected, with ISO 400 films showing lower resolution and sharpness than lower-sensitivity films.

  • It is noticeable that FX39 is much less compatible with the ISO 400 films than the other developers, especially since, according to the manufacturer, it is a further development of Neofin Red, a developer that was specifically designed for this film class.

  • It is also interesting to note that both XTOL and Wehner/Alpha with TMY (Tmax400) deliver outstanding results for resolution and edge sharpness, which are not matched by TMX (Tmax100), Delta100 and PanF.

Figure 2 shows the parameter pair resolution / development halo for the developers and films examined in six diagrams. The parameter ‘halo’ describes the width of the ‘hem’ of the dark stripes into the unexposed stripes.

Fig. 2: Parameter pairs for resolution and development halo

Discussion:

  • The most pronounced correlation between halo width and resolution is shown by FX39. Here, the resolution of high-sensitivity films is clearly limited by the widening of the dark stripes, since the contrast disappears even at a relatively low line density.

  • Wehner/Alpha shows the least tendency towards broadening in all films.

  • Of the ISO 400 films, TMY (Tmax400) shows the lowest halo values, which is one reason for this film's excellent resolution and high edge sharpness.

Figure 3 shows the parameter pair resolution / RMS granularity for the examined developers and films in six diagrams. The parameter of RMS granularity is a measure of the perceived graininess, more details can be found here.

Fig. 3: Parameter pairs for resolution and RMS granularity

Discussion:

  • Rodinal exhibits the most pronounced film grain, followed by FX39 and SD2525. The separation of the ISO 400 films from the films of lower sensitivity can clearly be seen.

  • D76, XTOL and Wehner/Alpha show no very pronounced correlation between RMS granularity and resolution, while the classic D76 has the narrowest range of variation depending of the type of film.