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:
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
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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.
$US899 for a “full pack”
iOptron SkyTracker Pro
Kenko Skymemo Tracker
Vixen Photoguider
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this is, in fact, a GP mount but without the declination part, and with a platform
for fixing two cameras. Also, the mount is more lightweight.
Star Adventurer 2
released in July 2020
essentially updates the version 1 by adding a very useful WiFi capability with a smartphone app
Integrated RJ-12 single-axis right ascension auto-guider port supports ST-4-type guiders
app can remotely control shutter on camera via cable connection
four AA batteries for 72hrs tracking or ext. USB power
11 lb payload capacity
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$AU529 for the “photo kit”
Star Adventurer
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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