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Fantasy MTF

Many manufactures publish what are properly termed fantasy MTF charts.

Here are some of the sneaky approaches used (and generally not documented):

Computing (not measuring) MTF. Real lenses never are quite as good as the design and often not symmetric across the field.
Computed MTF is another fantasy in itself: there are the tolerances of surface shapes, glass parameter variations (which batch?), and lens element placement all of which mean that MTF measured in a real lens never lives up to its computed theoretical performance.
Calculation of ray aberrations might be done monochromatically or with very narrow bandwidth: every lens looks considerably better if (for example) only a narrow range of green light is used.
Calculation often ignores diffraction, which truly makes the MTF chart pure fantasy defying the laws of physics, even assuming a perfectly assembled lens, because in a real lens diffraction is unavoidable.
While a claim might be made of “white light”, computations might be made in ways that effectively make it a monochromatic figure.

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Depth of field and how to bypass depth of field limitations via focus stacking.
Optical aberrations: what they are, what they look like, and what to do about them.
MTF, field curvature, focus shift: insight into the limitations of lab tests and why imaging performance is far more complex than it appears.
Optical aberrations: what they are, what they look like, and what to do about them.
How to test a lens for a “bad sample”.

Intrigued? See Focusing Zeiss DSLR Lenses For Peak Performance, PART ONE: The Challenges, or (one topic of many) field curvature.

Fantasy MTF chart that ignores diffraction
(computed, possibly with narrow bandwidth light)