The sharpness of a photographic imaging system is characterized by a parameter called Modulation Transfer Function (MTF), also known as spatial frequency response. It is the contrast at a given spatial frequency relative to low frequencies. High spatial frequencies correspond to fine image detail. The more extended the response, the finer the detail— the sharper the image.

In photogrammetry the extraction of features (Structure from Motion), which is a technique for estimating three-dimensional structures from two-dimensional image sequences, depends on the sharpness of the imagery recorded. Photogrammetric projects start with the calibration of imaging systems. The f-number of an optical system (such as a camera lens) is the ratio of the system's focal length to the diameter of the entrance pupil.


The objective of this project was to know at which f-number can be achieved the most sharp image. A test chart was imaged at different f-numbers and maintaining ISO and shutter speeds. The graphs bellow show that for this specific sensor, the f-number for getting sharp images is about six stops down from the widest aperture.