see also:

• astrophotography
• deep sky astrophotography
• guiders for astrophotography

• in order to avoid star trails when taking long exposures of the night sky, you need to have the camera sensor move with the earth's rotation
• the traditional method is to use an equatorial telescope mount but these are big and very heavy
• there are two other ways to achieve this:
  • in-camera sensor shift technologies have the potential for adjustments for relatively short exposures
  • smaller lighter portable tracker devices for your camera

• one should limit the load to only half the specified max. load limit to avoid straining the gears or having tracking problems
• you will also need:
  • Alt-Azimuth base or wedge to set your polar alignment
    • consider buying a much nicer base such as:
      • William Optics base mount which weighs just under 1kg and costs $US218 and comes in high latitude version for latitudes > 30deg and a low latitude tropics version
  • ball head to find your target eg. Benro IB2 ballhead

• alt-azimuth style with auto-correction of alt-azimuth field curvature up to 2 minute exposures with 85mm focal lengths
• uses smartphone app and the smartphone to do initial calibration without need to find north or south pole, then do a star alignment

• great for hiking and astrophotographic landscapes of the Milky Way
• only for light cameras and lenses and wide angle shots up to 135mm lens
• max. load “3kg”
• comes with alt-azimuth base
• 5hr battery, USB chargeable
• optional laser polar pointer (not useful for Sth Hemisphere) or sighting scope

• comes with declination and counter weight kit for larger camera lenses but the declination adjustments are too coarse for deep sky work at long focal lengths of 600mm
• built-in polar scope with illuminated reticle
• 20hr rechargeable battery
• can use optional autoguider
• included base is poor design with difficult knobs - consider buying a William Optics base
• issues with clutch quality issues
• max. load 5kg
• perhaps the best of the trackers for most people with the least issues

• as for iOptron SkyGuider Pro but instead of the polar scope it has a camera which requires use of a PC laptop for alignments
• useful for Sth Hemisphere
• $AU1199

• too bulky, heavy for hiking
• nice polar scope with reticle but no illuminator
• lots of cheap plastic covers eg. battery cover which fall off easily
• nice clutch - better than SkyGuider Pro and can use up to 600mm lenses
• much better base can do zenith for panos
• can use optional autoguider
• declination and counter weight bracket nice but not heavy enough for heavy lenses, although has nicer fine tuning knob
• 4x AAs = 72hrs but not rechargeable but can use USB power
• dial is easily moved which is likely to have it turned on while its in your backpack
• max. load 5kg
• great if you dont mind the weight and you decide to use USB power instead of batteries and tape the battery cover up

• adds WiFi for smartphone but not very useful
• $AU495 ($AU648 with declination/counterweight)

• some of these devices allow use of an optional auto-guider to correct by speeding up or slowing down (no declination correction usually) and this can allow nice star images with a 600mm lens up to 3-5 minutes instead of perhaps only 30secs without one
• requires a guidescope which is often attached to the camera hot shoe, or better still an L bracket, and a small camera for the guidescope which has 2 outputs:
  • USB cable to either:
    • your laptop (you also need software such as PHD2 which will lock onto a star and send commands to the tracker)
    • controller device such as ASIAir which then connects via WiFi to your smartphone
      • eg. https://agenaastro.com/zwo-asiair-plus-wi-fi-camera-controller-for-zwo-asi-cameras-asiair-plus.html
  • ST-4 cable to your tracker
• to enable dithering, you also need to connect your main camera to the laptop or the ASIAir via USB but this is probably more hassle than its worth
  • see https://www.peterzelinka.com/blog/2020/9/dithering-with-a-dslr-and-star-tracker
• examples of guidescope kits:
  • https://agenaastro.com/zwo-asiair-pro-wi-fi-camera-controller-kit-with-asi120mm-mini-camera-30mm-f-4-mini-guide-scope-asiair-pro-kit2.html $US497

• in order to increase effective acquisition time and reduce signal-noise ratio and thus dramatically reduce noise and improve image quality in the end photo, you generally need to take at least 10-15 images at the same camera settings then stack them in a software program then output to a 16 bit TIFF file for further post processing in a standard photo editing software such as Photoshop, LightRoom, etc
• many also take a series of:
  • dark frames at the same camera temperature and ISO
  • vignetting “flat” frames (take at same focus as light frames - shoot a flash with auto-exposure onto a even toned card placed in front of the lens)
  • bias or offset frames (take 10-20 shots at fastest shutter speed with lens cap on - temperature is not important but ISO must be same as your light frames)
• the stacking software will attempt to automatically align the stars in each image and provide you with various options on method of stacking as well as some will allow light pollution removal and star image distortion correction as well as removal of hot or cold pixels
• examples:
  • Sequator
    • free; Windows only
  • Deep Sky Stacker (DSS)
    • free; Windows only;
  • Astro Pixel Processor (APP)
    • introduced in 2017
    • runs on 64bit operating system (MacOS, Linux versions are available) with Java
    • currently € 165.00 for owner's licence (2021)
  • PixInsight
    • native 64-bit multi-threaded C++ application to FreeBSD, Linux, macOS and Windows operating systems
    • 230 Euros
    • example complex workflow combining a narrow field image of a comet with a wide field image: https://pixinsight.com/examples/NEOWISE/index.html