Abbe’s theory

In 1866, Ernst Abbe and Carl Zeiss cooperated together to improve the optical performance of microscopes. Only until then microscopes and microscope objectives were being produced by trial and error; some having exceptional optical performance but others having undesirable features. Abbe and Zeiss knew that they could only get an optimum and consistent performance on a complete theoretical basis. (Gundlach, 2005)

Abbe discovered after many calculations and experiments that the diffraction image in the back focal plane of the objective is essential for image formation. (Gundlach, 2005)

“No microscope permits components (or the features of an existing structure) to be seen separately if these are so close to each other that even the first light bundle created by diffraction can no longer enter the objective simultaneously with the non-diffracted light cone.” Ernst Abbe, 1873. (Gundlach, 2005)

Light rays diffracted by the specimen from the objective of an optical microscope are fundamentally important in Abbe's theory. Fine details of the specimen will not be visible, unless diffracted rays of light from the specimen are captured by the objective. (University, 2005)

Diffraction forms the image of light absorbing specimen. The light shows the specimen's structure consists of grating of different shapes of holes. A specimen will give a consistent bright image if the rays of light passes through the specimen undiffracted. Information is carried by the diffracted light over and around the structures of the specimen. (Logg, 2006)

When blocking different diffraction orders in the plot, as shown in figure 2,it shows the image of a grating (image to the left)The intensity of image of the grating should look like I grating. (Logg, 2006)]