> For the complete documentation index, see [llms.txt](https://docs.kostacloud.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.kostacloud.com/optimization/imaging-optimization/paraxial-metrics.md).

# Paraxial Metrics

Paraxial Metrics are provided to enable first order optical design capabilities.

### Assumptions

For all paraxial calculations in KostaCLOUD, We assume:

* The system can be represented as an unfolded system.
* The calculated sequence information is factual.
* We currently do not account for bifurcation of sagittal and tangential planes

For systems that break these assumptions, please use real-ray tracing routines. We have several of these operands which are approximated via real ray tracing.

### Effective Focal Length (Paraxial)

Effective focal length is defined as taking a first order ray parallel to the optical axis and tracing it through the optical system, and then calculating the distance in which this ray intersects with the original height.  

### Back Focal Distance (Paraxial)

**Details Coming soon**

### Front Focal Distance (Paraxial)

**Details Coming soon**

### Optical Invariant (Paraxial)

**Details Coming soon** 

### Front Principle Plane Distance (Paraxial)

**Details Coming soon**

### Rear Principle Plane Distance (Paraxial)

**Details Coming soon**

### Reduction Ratio (Paraxial)

**Details Coming soon** 

### Entrance Pupil Location (Paraxial)

**Details Coming soon** 

### Entrance Pupil Radius (Paraxial)

**Details Coming soon**

### Exit Pupil Location (Paraxial)

**Details Coming soon**

### Exit Pupil Radius (Paraxial)

**Details Coming soon**

### Image Space Numerical Aperture (Paraxial)

**Details Coming soon**

### Object Space Numerical Aperture (Paraxial)

**Details Coming soon**

### Image Height (Paraxial)

**Details Coming soon**

### Object Distance (Paraxial)

**Details Coming soon**


---

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