amsikking: Microscope objectives

Tube Lens

An infinity corrected objective needs an extra lens to form a finite image, often referred to as a 'tube lens'. In principle, any positive lens will work. However, in practice some care should be taken to ensure that the chosen tube lens can accommodate the pupil size (\(D_{BFP}\)) and the field of view (\(FOV\)) that the objective delivers (as well as the wavelength range and any final aberration corrections that may required). A useful reference is the manufacturer recommended tube lens, summarised below for the most popular manufacturers:

Here the field number (\(FN\)) is (in theory!) the field of view over which the tube lens (and maybe the objective!) can deliver diffraction limited performance (for a small enough pupil \(D_{BFP}\)). Note that the entrance pupil diameter (\(EPD\)) may cause vignetting (or the tube lens aberrations) for large enough pupils.