Four-Bar Width Calculator
Four-Bar Target Calculator
Pinhole Target Diameter Calculator
IFOV Calculators

Method #1: Requires you to know the camera’s FOV and total pixel length ( in x or y direction).
Method #2: Requires you to know the detector’s individual element size (microns) and the camera’s focal length (millimeters)

Universal Unit Converter for Conversions
This applet allows users to simulate standard optic elements (lens, mirror, dielectrics, sources, apertures) and observe the ways that light rays propagate through these elements. The applet is designed to be scripted but may also be used to construct optical systems using buttons and a click and drag metaphor.