Guiding exposure
Measure the guide star before the mount moves on.
Solve the exposure needed for centroid SNR and compare it with the mount-motion ceiling.
Purpose and method
What this calculator does
How long should my guide-camera exposure be? Find a guide exposure that measures the star before mount motion becomes excessive.
In words: The guide star must reach centroid SNR before the motion-limited cadence expires.
Change a value and the result updates immediately. The mount error rate is a local slope, not total periodic error. Multi-star guiding and seeing usually favour a cadence range rather than one exact value.
Working geometry
Guide cadence envelope
Guide-star signal must become measurable before uncorrected mount motion exceeds the allowed distance.
Inputs
Guide signal and mount motion
Calculated now
Guiding cadence
- SNR-limited minimum
- 0.84 s
- Motion-limited maximum
- 2.00 s
- Recommended guide exposure
- 0.84 s
- Requested SNR is feasible
- Yes
Governing equation
In words: Guide-star signal grows with time while photon noise, sky noise and read noise determine the centroid measurement quality.
Show the working
The calculator applies the equation above to the values currently entered, without rounding until this display.
- SNR-limited minimum
- 0.84 s
- Motion-limited maximum
- 2.00 s
- Recommended guide exposure
- 0.84 s
- Requested SNR is feasible
- Yes
The mount error rate is a local slope, not total periodic error. Multi-star guiding and seeing usually favour a cadence range rather than one exact value.