F-Ratio Image Brightness Factor
Same extended-source radiance/detector/throughput irradiance ratio under f-number²model, not point-source aperture photon ratio. Model only, not an ephemeris, measured stellar identity or observational guarantee.
Description
Extended-source image irradiance scales with the inverse square of focal ratio under matched conditions.
Extended-source image irradiance scales with the inverse square of focal ratio under matched conditions.1
That relation is distinct from point-source photon collection or sensor exposure limits. Use F-Ratio Image Brightness Factor to evaluate the supplied inputs under the model explained below.
When to use F-Ratio Image Brightness Factor
Use F-Ratio Image Brightness Factor to evaluate the supplied inputs under the model explained below. Establish the units, measurement scope and model assumptions before entering values.
How to use F-Ratio Image Brightness Factor and understand its results
- Establish the units, measurement scope and model assumptions before entering values.
- Enter First f number, Second f number using the field table and validation rules below, then run the tool.
- Read First over second extended source irradiance; interpret the units, signs, ordering and unknown-value placeholders described below.
- Correct reported input errors and rerun. Apply successful results according to their specific meanings and check the assumptions before using them in a decision.
| Input field | Meaning | Value type | Requirement |
|---|---|---|---|
| firstFNumber | First f number | number | Required; constraints below |
| secondFNumber | Second f number | number | Required; constraints below |
Enter two positive f-numbers. Return (second/first)² as first-over-second extended-source irradiance under otherwise matched conditions. No throughput, obstruction, pixel size or exposure setting is supplied.
firstOverSecondIrradiance=(secondFNumber/firstFNumber)² Use the field order, units and branch conditions described above.
| Output field | Meaning | Value type |
|---|---|---|
| firstOverSecondExtendedSourceIrradiance | First over second extended source irradiance | number |
{
"input": {
"firstFNumber": 2,
"secondFNumber": 4
},
"output": {
"firstOverSecondExtendedSourceIrradiance": 4
}
}Limitations and assumptions
That relation is distinct from point-source photon collection or sensor exposure limits. Apply the exact scope and assumptions explained above.
All listed fields require explicit values. Unexpected fields, incorrect types, nonfinite numbers and sparse arrays fail validation. Domain-specific bounds, alignments and supported tokens are explained above; extremely large inputs or outputs can also be rejected. Input errors differ from successful false results, empty match lists and unknown-evidence placeholders.
Alternative or Complementary methods
Use Light Gathering Power vs Eye Calculator for a related task: Clear collecting area and optical throughput affect relative photon collection.
Use True Field of View Eyepiece Calculator for a related task: A field stop limits the angular sky field passed by an eyepiece.
References
-
F-Ratio Image Brightness Factor — tool.io
Similar or alternative tools
- Light Gathering Power vs Eye Calculator
Clear collecting area and optical throughput affect relative photon collection.
- True Field of View Eyepiece Calculator
A field stop limits the angular sky field passed by an eyepiece.