In the excellent tutorial on MTF, http://www.luminous-landscape.com/tutoria.....shtml
the following summary points are made:
The closer the black and blue lines are, the better the lens is wide open
When the solid and dashed lines are closer to each other, the better the bokeh.
The higher up the chart the thick lines (10 LP/mm), the higher the contrast.
The higher up the chart the thin lines (30 LPmm), the higher the resolving power/sharpness
When thick lines are above .8, the lens will have excellent quality
Then, in the comparison of the Canon 400mm f/4 and the 100-400mm f/4.5-5.6http://luminous-landscape.com/reviews/lens...otten-400.shtml
examples show that the 100-400mm is a good deal softer.
What troubles me is that the MTF curves
included in the review for the 100-400 show that the thick lines are together at .98 at 20 which means, according to the tutorial, that the lens provides “high contrast” and is “better” wide open and, being greater than .8, of excellent quality. The thin lines being “close” at about .8 also favor quality at wide open and “better” sharpness.
Further, the solid and thin lines for the 100-400mm are higher than those of the 400mm prime. Except for the higher positions of the dashed line for the prime, one would think the zoom is superior.
Can anyone provide any perspective on this? Might the softness that appears in the test shots be the result of focusing? Considering the differences in dashed line positions, is the pictured softness a bokeh issue?