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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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Imaging

Seeing-based focal length

AllField of viewSamplingImage scaleFocal ratioFocal length for seeingEyepieceBinocularsResolving powerDust shadowGuide scope

Camera

µm
Binning

Sky

″

Goal

2.0 pixels per FWHM
Effective focal length
517mm
Image scale
1.50″/px
Native, with your reducer
517 mm

An effective focal length of about 517 mm puts 2.0 pixels across a 3.0″ star with 3.76 µm pixels.

f = 206.265·p·b·n / seeing = 206.265·3.76·1·2.0 / 3.0 = 517 mm

This is the effective focal length. With your 1.00× reducer/Barlow the telescope’s own focal length is the result divided by 1.00.