Detected signal ∝ NA² × Transmittance × (1/Mag²) × Pixel Area × QE. Higher NA collects more light (∝NA²). Lower magnification concentrates photons on fewer pixels (∝1/Mag²). Larger pixels collect more photons per pixel. Higher QE converts more photons to electrons. These factors can compensate for each other, allowing different configurations to achieve equivalent sensitivity.
Design Principle
Sensitivity Trade-offs
The photon budget equation
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Definition
The interplay between optical and detector parameters that determines how efficiently the system converts sample fluorescence into detected signal. Understanding these trade-offs enables optimal system design for specific applications.
Technical Details
Simplified
Getting a bright signal depends on many factors working together: how much light your lens collects, how it's spread across pixels, how efficiently those pixels detect light. A cheaper system might match an expensive one if the factors balance out right.
Why It Matters
Understanding sensitivity trade-offs prevents over-specifying expensive components. A 25× 1.1 NA objective with 3.7μm pixels can match the per-pixel signal of a 60× 1.2 NA objective with 6.5μm pixels, while providing 5× more field of view.
Practical Example
E9 at 25×: NA²=1.21, large sample/pixel. Kinetix at 60×: NA²=1.44, small sample/pixel. The 19% higher NA² of the 60× system is offset by concentrating photons on larger sample area per pixel in the 25× system.