Editing Objective (optics) (section)

===Objective pupil diameter===
The objective pupil diameter<ref name=microscopeUInfinity />, also known as entrance pupil diameter<ref>{{cite web | title=Imaging Microscope Objectives, Dry | url=https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=1044 | website=Thorlabs | publisher=Thorlabs, Inc. | access-date=2025-05-17}}</ref> or back aperture diameter, refers to the diameter of the rear opening of an objective lens. In dry infinity corrected objectives, this diameter <math>D</math> is

<math> D = 2 \times NA \times f_{obj}</math>

where <math>NA</math> is the numerical aperture, and <math>f_{obj}</math> is the effective focal length. Magnification <math>M</math> and effective focal length are related by<ref>{{cite web | title=Infinity Microscope Basics | url=https://asiimaging.com/docs/infinity_microscope_basics | website=Applied Scientific Instrumentation | publisher=ASI | access-date=2025-05-17}}</ref>

<math> f_{tube} = M f_{obj}</math>

where <math>f_{tube}</math> is the tube lens focal length. Tube lens focal lengths vary by manufacturer: Leica and Nikon typically use 200 mm, Olympus uses 180 mm, and Zeiss uses 165 mm<ref name=microscopeUInfinity />.