Phase Plates in an Objective Lens for Biological Specimens

As explained in Sec. 7.1.7, ordinary TEM imaging based on the WPOA has less image transfer for spacing larger than 1 nm due to the imaginary part of CTF, \(\sin \gamma \left( u \right)\) . Non-stained biological specimens are almost phase objects because they are composed of light elements. We do not have an effective image contrast in TEM.