photo:star_trackers
motorised star trackers
see also:
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)
- iOptron SkyGuider - iPolar
- 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
- Kenko Skymemo Tracker
- 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
- 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.
- Star Adventurer 2i
- 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
- $AU529 for the “photo kit”
- Star Adventurer
- large design so not great for backpacking with (iOptron SkyGuider Pro might be a better choice)
- nice declination bracket (much better than on the iOptron SkyGuider Pro, so better for telephoto use)
- periodic error is around 50 arc-seconds
- with good set up, can record up to 30secs with a full frame focal length of 200mm for pin sharp stars (hence you may need to take over 50-300 images at 30secs, ISO 1600, f/4 then stack them), but for longer exposures, one needs to resort to a two axis autoguider (see below) to get good star shapes
- flimsy plastic battery cover and polar scope cover
- rotary dial can accidentally turn on during transport
- ZWO AM5
- Go-To mount that does not need balancing weights thanks to its harmonic drive but limited to 900mm focal length scopes (for larger scopes you can add the optional counterweight bar and pier extension)
- position controlled by WiFi joystick or ASI Mount smartphone app but thi is very basic compared to the ASI Air (see below)
- used by Peter Zelinka https://www.peterzelinka.com/blog/2023/2/2023-astro-gear-recommendations
- combine with:
- ZWO ASIAIR Mini Wi-Fi Smart Camera Controller or ZWO ASIAIR Plus Wi-Fi Smart Camera Controller (with 32GB eMMC Memory) which also has a USB 3.0 ports, a power switch, 2 more 12V ports.
- Handles polar alignment without using polar stars by using plate solving from images from your main camera then tells you how much to adjust azimuth and latitude
- handles autofocus of telescpes when using the ZWO Electronic Automatic Focuser (EAF)
- handles guiding, and more
- use 5A 12V 60W DC input
- Distributes 12V power to all of your astrophotography accessories
- Works with ZWO cameras and many DSLR & mirrorless cameras
- 12Gb of the internal memory is used by firmware and star atlas, can also add microSD card (up to 1Tb?)
- Benro Polaris with Astro Kit
- has the advantage that it does not need polar alignment
- works via the phone app
- ~$AU2399
photo/star_trackers.txt · Last modified: 2024/10/22 13:39 by gary1