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

the new strain wave design / harmonic mounts are fantastic for portability and avoids need for counterweights BUT for good results, you need to have an autoguider for imaging with them!
- strain wave mounts are really tricky - the constant motion means guiding images need to be good enough at 0.5-1s refresh vs the more necessary 2s for most with OAGs on traditional mounts
- not as good in windy conditions
- unlike traditional mounts, if they lose power the scope may slowly rotate to the bottom unless there is a RA auto-brake that prevents this
- they usually specify a torque in Nm for use without a counterweight and this allows you to ascertain your max. weight of your scope system you can use:
  - eg. the max. 16Nm rated Nema14 34mm stepper motor and the centre of your scope axis / centre of mass is 20cm from the mount axis then 16/0.2m = 80N = 8kg (as 80N = 8kg x 9.8 m/s gravity)
- a brushless servo motor with encoder feedback loop is better than stepper motor as:
  - much faster reaction time to start moving: stepper motors 100-200msec servos < 10msec
  - higher torque allowing faster reaction to moving it, but does need an encoder feedback loop system (these are often low end encoders lacking high precision)
  - a high end precision encoder with a servo motor is considered most accurate than stepper motors as even though a stepper motor should move a specific amount, it does not mean it actually does move that amount (wind, out of balance, overweight, resistance in system, gear backlash, etc.), hence an encoder / closed loop is used on higher end scopes.
  - a downside of a servo is that they can get burnt out as they do not like forced stops when turned on such as the scope hitting into a wall - but some will have protections for this
- https://www.youtube.com/watch?v=7WaTIGueiwc

Portable motorized star trackers

Move Shoot Move updated Nomad Sth Hemisphere version:
- see https://www.youtube.com/watch?v=If73l_8Gxds
- great portable, light option for astroscapes and cameras up to 135mm focal length and does well with 85mm 90sec shots
- easy sth hemisphere alignment using a smartphone attached to mount (need to calibrate phone first by doing a figure of 8) and an app such as Sky Safari 7 Plus for Android or similar for iOS eg. PhotoPills
  - when you are polar aligning with the phone mount the phone is aligning down to the north celestial pole so when the tracker is mounted it is pointing up and therefore aligned to the south celestial pole
  - smartphone alignments are not as accurate so do limit exposure durations
- the rotating base requires a tripod with a small base plate - the locking screw ends lower than the Arca-swiss plate and when installed on a tripod with large diameter base plate such as a Gitzo and the screw rubs against the plate, making it impossible to use it at all
- optional: camera rotating collar mount such as:
  - Silence Corner Atoll S Rotating Collar for Sony cameras https://www.amazon.com.au/Silence-Corner-Rotating-Mirrorless-Cameras/dp/B0BJDQMDQS/
- https://www.moveshootmove.com/products/phone-kit-for-polar-alignment-inspired-by-richard-tatti $US399 free shipping
- https://siderealtrading.com.au/product/move-shoot-move-southern-hemisphere-astrophotography-kit/ $AU695
- for heavier cameras, a Skywatcher Star Adventurer is a more robust option and has a counter weight system
iOptron SkyGuider Pro
- https://www.ioptron.com/
- issues with use at latitudes > 40deg
- declination module not great
- 11lb weight limit
MIOPS Capture 360
- 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
- https://www.ioptron.com/
- entry level; not weathersealed;
- only 2.6lb weight limit
- counterweight kit is a poor design ¹⁾
iOptron SkyGuider - iPolar
- https://www.ioptron.com/
- 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
iOptron SkyHunter Portable EQ/AZ GOTO Mount with iPolar
- ?2022 model
- Vixen dovetail saddle; incl. counterweight;
- attaches to a camera tripod with 3/8” or 1/4” threads
- built-in Li poly 3.7V 2000mAh rechargeable battery for up to 10 hours of operation - MiniUSB charging
- built-in WIFI adapter for full ASCOM, iOptron CommanderTM and SkySafari control
- can be controlled by a SkySafari 6 Pro or later on an iOS or Android smart phone/tablet, an optional 8410 hand controller, or a computer via ASCOM, INDI or embedded drive.
- iPolar still needs a PC to set up?
- max slew 4.5°/sec
- 1.3kg, max payload 3.2kg;
- https://www.ioptron.com/product-p/3700eqa.htm $US648
- optional Go2Nova® 8410 controller with Advanced GOTONOVA® GOTO Technology
- will work with ASIAIR Mini Station mode but not with ASIAIR Pro - see https://www.youtube.com/watch?v=iRAEOeXb2_s
iOptron HAE18C AZ/EQ dual SWG
- https://www.ioptron.com/product-p/he182c.htm $US1548
- similar in concept, weight and payload to the ZWO A3N but no Bluetooth and PE rated at < 36 arcsec
- strain wave equatorial mount Vixen saddle with on saddle USB-C and 12V ports for easier cable management
- can be controlled by a computer, either via ASCOM/Commander for a Windows PC or a third party INDI driver for a MacOS software; a Smartphone/Tablet via iOptron Commander Lite or an App like SkySafari Pro; or a Raspberry Pi device via INDI driver, “C” models (internal main board versions) with built-in Wi-Fi allow for external control without need for a handset
- optional wired 8411 Go2Nova® handset controller ($US226)
- Optional iPolar electronic polar scope ($US173)
  - can be easily installed inside the RA shaft on all iOptron equatorial mounts (except SmartEQ Pro)
  - works globally, no need to set northern and southern hemispheres and does not need to visualise the polar stars
  - requires a PC via USB to work - no smartphone or Android software
- Optional counterweight shaft (#P-SGP-CWS) and counterweight (#3006-05)
- 2.82kg max payload 8.5kg;
- there are larger models at https://www.ioptron.com/category-s/264.htm
Kenko Skymemo Tracker
- http://www.sciencecenter.net/hutech/kenko/skymemo/index.htm
- It can be attached to a photographic mount, so there is very little extra weight in addition to the ordinary photographic gear required.
Vixen Photoguider
- http://www.teleskop-service.de/Vixen/Astrofotografie/astrofotografie.htm#PhotoGuider
- this is, in fact, a GP mount but without the declination part, and with a platform
  for fixing two cameras. Also, the mount is more lightweight.
Sky Watcher Star Adventurer 2i
- released in July 2020
- for cameras up to 200-300mm or small telescopes
- 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
- polar illuminator not supplied to Australian markets due to ban on button batteries
- https://skywatcheraustralia.com.au/product/sky-watcher-star-adventurer-2i-photo-package/
- $AU529 for the “photo kit”
- https://siderealtrading.com.au/product/star-adventurer-pro-pack/ $AU649 for pro pack
Star Adventurer
- see http://philhart.com/content/star-adventurer-review
- 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
Teseek 14 SWG/Harmonic mount
- budget SWG mount with BT, WiFi, can use ASiair, only 2.53.5°/s slew; green laser for polar alignment - but can use ASiair instead
- https://www.youtube.com/watch?v=u1v4Vu0X1u0&t=21s - good mount for the discounted price of $US500
- https://www.aliexpress.com/item/1005009322172178.html ~$AU1200-1300
Proxisky UMi 17 Lite
- 2.8kg; older stepper motor version
- https://www.proxisky.com/
- https://www.cloudynights.com/topic/922489-umi-17-lite-harmonic-drive-mount-quick-review/
Proxisky Umi 17S
- servo motors with anti-collision but only at default speed, not stepping motors; usual slew 3.5°/s, max 7°/s.
- 3.5kg, max payload 14kg w/o counterweights
- works with ASIair
- https://www.proxisky.com/ $US2199
- https://www.youtube.com/watch?v=Z5MPjAv7FM8
ZWO A3N 2025 version
- harmonic drive mount; 12V DC 5.5 × 2.1 mm, center positive uses 1.3A GoTo, 0.8A tracking; 3.9kg (4.8kg in case) ~$US1699
- mount compatible with Losmandy (D Style) or Vixen (V Style) dovetail bars - you would need to add a tripod mount for your camera if it is not attached to a scope with these bars
- max payload 8kg (13kg with counterweight) but otherwise similar to ZWO AM5 although lacks a side mount but 2025 model A3N adds Bluetooth and dovetail saddle now includes both a Type-C and 12V DC output port.
- works effortlessly with ASIAIR Plus, ASIAIR Mini, and other ZWO products for easy automation and control
- wired hand controller (or WiFi vi ASI Air) as per AM5
- Max Slew Speed: 6°/s
- periodic error is consistently controlled within ±15 arcseconds.
- https://agenaastro.com/zwo-am3n-strain-wave-drive-equatorial-mount-head.html
- https://bintel.com.au/products/zwo-am3n-harmonic-drive-mount $AU2799
- I am guessing it may work best on their dedicated tripod and silver plate to attach to the 4 mount holes https://agenaastro.com/zwo-tc40-carbon-fiber-tripod.html
ZWO AM5
- Go-To mount that does not need balancing weights thanks to its harmonic drive but limited to 900mm focal length scopes (for larger scopes you can add the optional counterweight bar and pier extension)
- harmonic drive mount;
- supports 15kg without counterweights, 20kg with counter weight up to 5kg via an optional M12 × 1.75 coarse threaded shaft max 25cm long
- position controlled by wired or WiFi joystick or ASI Mount smartphone app but this is very basic compared to the ASI Air (see below)
- used by Peter Zelinka https://www.peterzelinka.com/blog/2023/2/2023-astro-gear-recommendations
- https://agenaastro.com/zwo-am5n-strain-wave-equatorial-mount-head.html
- 5.5kg; $US2499 / ~$AU3200
- combine with:
  - ZWO ASIAIR Mini Wi-Fi Smart Camera Controller or ZWO ASIAIR Plus Wi-Fi Smart Camera Controller (with 32GB eMMC Memory) which also has a USB 3.0 ports, a power switch, 2 more 12V ports.
    - Handles polar alignment without using polar stars by using plate solving from images from your main camera then tells you how much to adjust azimuth and latitude
    - handles autofocus of telescopes when using the ZWO Electronic Automatic Focuser (EAF)
    - handles guiding, and more
    - use 5A 12V 60W DC input
    - Distributes 12V power to all of your astrophotography accessories
    - Works with ZWO cameras and many DSLR & mirrorless cameras
    - 12Gb of the internal memory is used by firmware and star atlas, can also add microSD card (up to 1Tb?)
Emcan Astro EM31Pro
- similar to ZWO AM5 specs but “premium version”, 4kg, NEMA42 stepper in Dec instead of NEMA35; max payload w/o c/weight 15kg; RA brake; OnStep;
- https://www.youtube.com/watch?v=_XRivEhZrWQ
  - fantastic $US400 tripod and polar alignment manual controls
- https://www.aliexpress.com/item/1005006667063169.html
Benro Polaris with Astro Kit
- has the advantage that it does not need polar alignment BUT seems to have lots of bugs although this could be user error - see https://www.youtube.com/watch?v=MU3sLxOFvRQ
- works via the phone app
- seems to only give adequate star tracking for focal lengths to 200mm (maybe 300-400mm)
- ~$AU2399
- https://www.siderealtrading.com.au/product/benro-polaris-astro-3-axis-smart-electric-tripod-head/
- https://www.siderealtrading.com.au/reviews/getting-an-image-of-a-comet-using-the-benro-polaris/
MLAstro SAL-33
- all aluminium; harmonic drive mount; zero-shift alignment tightening technology
- 5.3kg https://mlastro.com/mlastro-sal-33 $US1099
- https://www.youtube.com/watch?v=zCZlWhuuoFQ

¹⁾

https://www.youtube.com/watch?v=adM8P_Asd5w