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Plan

  • Tonight
  • Night Outlook
    • Weather
  • Targets
    • Saved targets
  • Plan a night
  • Night plans
    • Logbook

Tools

  • Sky atlas
  • Field of View
  • Exposure Lab
  • Calculators
  • Horizon Studio
  • Sequence Studio
    • Nights
    • Projects

Setup

  • Settings
  • About & Support
  • What’s new

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Sky & timeNew

Polar alignment tolerance calculator

How good must my polar alignment be?

All 16 calculators
Polar alignmentTripod trailingSky darknessPlanetary imaging

Polar alignment

′
s

Telescope

mm
Reducer / Barlow
×

Camera

µm
Binning

Telescope, camera and sky are shared by every calculator in this visit and kept in the link.

Stars elongate unguidedDrawn to scale

Worst-case drift per sub

3.05px

A 5.0′ alignment error drifts up to 3.9″ in a 180 s sub — 3.0 pixels. Keep it under 1.6′ for at most one pixel; guiding removes this drift.

Drift per sub
3.94″
Drift rate
1.31″/min
Error allowed for ≤ 1 px
1.6′

With your numbers

drift ≈ E·2π / T_sid (T_sid = 1436 min, worst case)

= 5.0′ · 3.00 min · 0.2625″/(′·min) = 3.94″

3.94″ / 1.29″/px = 3.05 px

Worst case, near the meridian and the celestial equator. Guiding corrects it; field rotation is a separate effect.