It is interesting to note what happens under different sky
conditions. If the sky is white, the character of the blend changes and the
mirror position for best blend shifts slightly, by an amount too small to
correct, at least in the first printer. At the best blend position the blend
looks like a darker purplish line in the center of a lighter blend. This
follows from the typical emulsion characteristics. For very dense skies or
panels, the matchline changes character in the opposite sense taking on the
appearance of a light band with dark edges (although the dark edges are often
not apparent in the dark scene) and also requires a mirror shift for best blend
by a small amount. There is sometimes a very slight uncorrectable color shift.
In the picture, there is one scene where the camera is half submerged where
both effects (white sky and dense water) are present in the same matchline.
When the sky is blue we have an example of a color shift.
Here there is good exposure in the cyan color layer and very little density in
the yellow and magenta layers of the emulsion so that these last two layers are
relatively unresponsive to the feather exposure. The feather therefore takes on
a blue cast. Where the sky runs from deep blue-cyan at the top to white haze
near the horizon, it is possible to see the blue line shading to magenta near