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AstroBrainCalculators
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  • Sky atlas
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    • Weather
  • Exposure Lab
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Setup

  • Settings
  • About & Support
  • What’s new

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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Visual

Resolving power calculator

AllField of viewSamplingImage scaleFocal ratioFocal length for seeingEyepieceBinocularsResolving powerDust shadowGuide scope

Telescope

mm

Test pair

″
Split
Dawes limit
0.97″
Rayleigh limit
1.15″
Pair shown
1.15″

In steady air a 120 mm aperture separates equal stars about 0.97″ apart.

Dawes = 116 / D = 116 / 120 = 0.97″ · Rayleigh = 138 / D = 138 / 120 = 1.15″ · 1.22·λ / D (λ = 550 nm) = 1.153″

Ideal optics, unobstructed aperture, 550 nm, no seeing.