EO 120i Plan APO 無限補正対物レンズ

Technical Note: Why Numerical Aperture Does Not Define Performance

Numerical aperture (NA) is an important specification to define for a microscope objective because it describes the objective’s ability to gather light at a fixed working distance. The NA is often assumed to describe an objective’s resolving power; however, this is not an accurate assumption. The equation below is the first-order equation used to calculate NA. This equation is useful for understanding NA on-axis, but it does not consider field changes for off-axis performance. In addition, this equation does not consider tolerances during the manufacturing and assembly of microscope objectives that can impact the performance.

n: refractive index of imaging medium

θ: one-half of the objective’s opening angle

Figure 1 below demonstrates the off-axis performance of the 5X 120i Plan APO Infinity Corrected Objective compared to another 5X Plan APO infinity corrected objective from another manufacturer that has the same NA of 0.14. Performance off-axis is better with the 120i Objective in the corner of a 1.1” sensor, indicating that NA is not the defining factor for the performance of an objective.

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