Originally posted by Lowell Goudge this is all about loss of contrast due to internal reflections.
most specifically a measure of the quality of the coatings.
for many years pentax was regarded as having absolutely the best coatings.
Apparently, the coatings and internal reflections are only a part of the problem. However, the veiling flare is the one thing that remains somewhat in the control of the photographer, so is the most important aspect to us.
As in my experiments with the 16-45 an 43, it seems to me there is
compression that can be dialled in by the designer, and this compression when done right gives the illusion of greater contrast and saturation.
It's easy enough to see using photoshop and the levels tool. And easy enough to verify as occurring using a couple of lenses with different characters.