Rule of 500 Astrophotography Shutter
Caller explicit historical 500-rule exposure heuristic, not pixel-accurate star-trail tolerance or guaranteed sharp exposure. Model only, not an ephemeris, measured stellar identity or observational guarantee.
Description
Astrophotography shutter heuristics relate focal length to a tolerance for apparent star motion.
Astrophotography shutter heuristics relate focal length to a tolerance for apparent star motion.1
A named rule's numerator is a chosen assumption rather than a guarantee of sharp stars. Use Rule of 500 Astrophotography Shutter to evaluate the supplied inputs under the model explained below.
When to use Rule of 500 Astrophotography Shutter
Use Rule of 500 Astrophotography Shutter to evaluate the supplied inputs under the model explained below. Establish the units, measurement scope and model assumptions before entering values.
How to use Rule of 500 Astrophotography Shutter and understand its results
- Establish the units, measurement scope and model assumptions before entering values.
- Enter Focal length mm, Caller sensor crop factor, Caller heuristic numerator using the field table and validation rules below, then run the tool.
- Read Heuristic shutter seconds; 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 |
|---|---|---|---|
| focalLengthMm | Focal length mm | number | Required; constraints below |
| callerSensorCropFactor | Caller sensor crop factor | number | Required; constraints below |
| callerHeuristicNumerator | Caller heuristic numerator | number | Required; constraints below |
Enter positive focal length in mm, crop factor and independently chosen heuristic numerator. Divide numerator by focalLength×cropFactor to return seconds. The title's 500 is not installed; no declination, pixel pitch, trail test or shutter control is included.
heuristicSeconds=callerNumerator/(focalLengthMm×cropFactor) Use the field order, units and branch conditions described above.
| Output field | Meaning | Value type |
|---|---|---|
| heuristicShutterSeconds | Heuristic shutter seconds | number |
{
"input": {
"focalLengthMm": 50,
"callerSensorCropFactor": 1,
"callerHeuristicNumerator": 500
},
"output": {
"heuristicShutterSeconds": 10
}
}Limitations and assumptions
A named rule's numerator is a chosen assumption rather than a guarantee of sharp stars. 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 NPF Rule Approximate Shutter Pixels for a related task: NPF-style exposure estimates use optics, pixel pitch and declination.
Use Barlow Effective Focal Length for a related task: A Barlow changes effective focal length according to its matched gain.
References
-
Rule of 500 Astrophotography Shutter — tool.io
Similar or alternative tools
- NPF Rule Approximate Shutter Pixels
NPF-style exposure estimates use optics, pixel pitch and declination.
- Barlow Effective Focal Length
A Barlow changes effective focal length according to its matched gain.