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photo:star_trackers

motorised star trackers

Introduction

  • the greater the magnification, the greater the effect of the rotation of the earth to cause “star trails”
  • a 50mm lens on 35mm full frame shows star trails if exposures are greater than 8secs
  • maximum exposure times are inversely proportion to effective focal length, thus 25mm lens can expose for 15secs
  • this can be minimised by automatically moving your camera at the same speed as the earth rotates using a motorized equatorial mount star tracker or mounting your camera on a telescope with such a mount.
  • for critical work at longer focal lengths and longer exposures for deep sky photography you need a more sophisticated set up which would include:
    • a high quality, expensive, heavy, equatorial mount with:
      • a very low periodic error
      • excellent polar alignment
      • good weight balancing
      • automatic guidance correction system such as a separate scope with a photo sensor and an auto guiding system which allows the user to have that scope lock onto a relatively bright contrasty subject such as a star or comet and the system will then make small continuous adjustments to the motor tracking system
      • see astrophotography for more links and details
  • for less critical work a smaller, more portable and less expensive tracker can be used
    • there are many types of the market, some are mention below
    • these will generally allow focal lengths of up to 135 or 200mm to be used often at exposures up to 30secs with good results if set up well
    • they generally only have a motor on the RA axis and some will accommodate a RA-only autoguider functionality

Portable motorized star trackers

  • iOptron SkyGuider Pro
    • issues with use at latitudes > 40deg
    • declination module not great
    • 11lb weight limit
    • Available Dec 2018, uses 2-3 Bluetooth controlled Capsule 360 units with L bracket mounted on a tripod set to latitude and aimed at the pole, for camera kits up to 7kg if mounted in centre.
    • extremely versatile, can be used for many video timelapse and subject tracking purposes as well.
    • $US899 for a “full pack”
  • iOptron SkyTracker Pro
    • entry level; not weathersealed;
    • only 2.6lb weight limit
    • counterweight kit is a poor design 1)
  • Kenko Skymemo Tracker
  • Vixen Photoguider
  • Star Adventurer 2
    • released in July 2020
    • essentially updates the version 1 by adding a very useful WiFi capability with a smartphone app
    • Integrated RJ-12 single-axis right ascension auto-guider port supports ST-4-type guiders
    • app can remotely control shutter on camera via cable connection
    • four AA batteries for 72hrs tracking or ext. USB power
    • 11 lb payload capacity
    • $AU529 for the “photo kit”
  • Star Adventurer
    • large design so not great for backpacking with (iOptron SkyGuider Pro might be a better choice)
    • nice declination bracket (much better than on the iOptron SkyGuider Pro, so better for telephoto use)
    • periodic error is around 50 arc-seconds
    • with good set up, can record up to 30secs with a full frame focal length of 200mm for pin sharp stars (hence you may need to take over 50-300 images at 30secs, ISO 1600, f/4 then stack them), but for longer exposures, one needs to resort to a two axis autoguider (see below) to get good star shapes
    • flimsy plastic battery cover and polar scope cover
    • rotary dial can accidentally turn on during transport
photo/star_trackers.txt · Last modified: 2020/08/28 12:10 by gary1