Canon’s newly announced 40mm f/2.8 STM lens looks pretty sharp.  Below are the MTF charts for the 40 and the closely related 50 f/1.8 and f/1.4.  Below that is my lovely sketch of what it all means and a brief explanation.  I am not one for pixel peeping and agonizing over these charts, there are lots of other measures of the value and of a lens, but this can give us some idea of sharpness/contrast and resolution.  Click the images below for a larger view.


MTF Chart of the 40mm f/2.8, 50mm f/1.8 and 50mm f/1.4


An MTF chart is made by taking a photo of a bunch of lines very, very close together, and then the image is inspected.  How well the photo displays the individual lines is then graphed.  Looking at my excellent sketch below, the x-axis is distance from the center of the lens to the edge of the lens.  This number will vary for different lenses depending on the lens diameter.  The y-axis is, basically, how well the lens does.  Blue line is results at f/8, this is usually near the sweet spot – sharpest aperture, of any lens and the black line is the result of shooting with the lens at it’s widest aperture, this will vary by lenses.  In the example above the black line represents f/2.8, f/1.8 and f/1.4 as that is the widest aperture of each lens as listed from left to right above.  You also see thick lines and thin lines, thick lines represent contrast reproduction abilities and thin lines represent resolving power/sharpness.

How to read MTF charts


Luminous Landscape has a more detailed overview

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