Glare and flare look the same, and are usually referred to as simply glare, as the two are inseparable. Where glare goes, flare follows in lens systems. Cytologic preparations are often thicker than histologic preparations and so require more stringent mounting conditions. An upside down slide will be imaged satisfactorily under 10X, but can not be imaged at all under 40X. Evaluating cover glass alternatives under 10X will result in a passing grade, but not if evaluated under 40X objectives. Power for power, apochromat objectives are more sensitive to cover glass and mounting medium thickness than achromat objectives, since they have higher numerical apertures.
Numerical aperture is THE factor that determines thickness sensitivity.
Since the loss of image contrast resulting from spherical aberration and glare look identical, it is important to recognize the various contributing factors so one can systematically troubleshoot these problems. By thus reducing the working NA, the microscopist is increasing the objective's tolerance to thick mounts and so can image them sharply. Closing the aperture diaphragm too far, however, creates an unacceptable refractile appearance due to diffraction effects. Quality outcomes are based on quality processes, not the other way around. Our dream is to provide great and innovative solutions for online education and professional services in the field of cytopathology and pathology.