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Plan

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

Tools

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

Setup

  • Settings
  • About & Support
  • What’s new

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Workshop

Guide scope scale calculator

AllField of viewSamplingImage scaleFocal ratioFocal length for seeingEyepieceBinocularsResolving powerDust shadowGuide scope

Guiding

mm
µm
Guide binning

Telescope

mm
Reducer / Barlow
×

Camera

µm
Binning
Comfortable
Guide / main
2.5:1
Guide scale
3.22″/px
Main scale
1.29″/px

Your guide camera sees 3.22″ per pixel, 2.5× coarser than your main camera.

s_g = 206.265·3.75·1 / 240 = 3.22″/px · s_m = 206.265·3.76·1 / 600 = 1.29″/px · R = s_g / s_m = 2.49

A rule of thumb: star brightness, signal-to-noise and seeing matter as much.