4. Optimum aperture

 

Most lenses don’t achieve maximum sharpness when the aperture is wide open, they need to be closed down a little.
Sharpness continues to improve until the impact of diffraction becomes apparent.
Somewhere in between is the lens’s optimum aperture at which it produces the sharpest images.
You can identify the optimum aperture of a lens by shooting a subject with plenty of detail at every available aperture.
It’s essential that the camera is mounted on a solid tripod and that you focus on exactly the same spot.
Then examine the images at 100% on screen to find the image that shows the subject sharpest and check the EXIF data to find which aperture was used.
This is the lens’s optimum aperture.

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