« on: March 11, 2012, 06:30:51 AM »
This shows where the 135mm f/2L MTF chart stands against the MTF chart of Canon's top performing prime the 400mm f/2.8L IS II. Two completely different lenses, of course, but it shows just how remarkable Canon's current lens technology is, and how much the 135 could be improved. In simplified terms... the higher the lines and the closer they track each other the better the quality of the lens.
Unfortunately, that's a bit of an oversimplification.
Here's the MTF chart for the 14mm f/2.8L II:
Does it mean that the 14L II is a hunk of junk compared to the 400L II? Of course not. It's one of the best 14mm SLR lenses available today. Basically, MTF charts are very useful for comparing lenses of the same focal length, but comparing the 135L's MTF to the 400L II's is apples & oranges.
Luminous Landscape has a very good tutorial on reading MTF charts.
To quote Michael's article:
Keep in mind that the black lines show the lens wide open while the blue lines show the lens stopped down to f/8, so the closer these sets of lines are to each other the better the performance of the lens when used wide open. The very best lenses will have the black and the blue lines close together.
Generally speaking a lens whose thick lines (10 LP/mm) are above .8 on the chart should be regarded as having excellent image quality. Above .6 is regarded as "satisfactory". Below .6 is, well, below.
[...] The closer [the dotted meridonial and sagital] lines are to each other the more pleasing the bokeh of the lens. Fascinating, huh?
The meridonial and sagital lines are also used used to evaluate astigmatism and field curvature — subjects which are beyond the scope of this brief essay.
It's also worth mentioning that anything after the 16mm mark on the X-axis is irrelevant on APS-C cameras...