Capturing sweeping vistas of the Milky Way or detailed shots of the constellations used to mean you had to piggyback your camera on a telescope before you could track the movement of the stars across the night sky.
These days we are spoiled for choice, as several manufacturers have added tracking capability to basic camera mounts.
The latest of these is the iOptron SkyGuider mount for DSLRs.
The SkyGuider has an integrated illuminated polarscope and is supplied with a 12V power cable, polarscope cable, small counterweight, basic instructions and a soft padded case.
Also included is a tripod, which has its own soft case.
Unlike iOptron’s smaller SkyTracker unit, the SkyGuider is a modified lightweight version of the company’s ZEQ25 equatorial mount.
The modification is that there is no declination axis, so you do need to buy a ball head to mount a camera or small telescope in order to achieve full flexibility in framing up targets.
Assembly proved reasonably straightforward.
Instead of installing the counterweight shaft and weight, a second ball head can be attached, allowing you to create a dual imaging setup – useful if you would like to use a guidescope or for meteor imaging.
The mount’s simple but effective spirit level enables you to level it before polar alignment.
The latter is a breeze, especially if you have an Android or iOS phone or tablet, as iOptron has also developed a very useful app that shows exactly where to place Polaris in the illuminated field of view of the polarscope.
The mount can be set from 0-60° latitude for either hemisphere, so it is suitable for trips to many dark-sky sites abroad.
It is certainly portable, with the mount head weighing in at just 2.6kg.
The mount interface offers several options, including northern or southern hemisphere tracking.
A four-way switch allows you to choose your tracking rate from normal sidereal, 0.5x sidereal, lunar and solar.
The last two are useful for imaging eclipses involving the Sun or the Moon, while the 0.5x sidereal rate allows for wide-field exposures so you can keep foreground objects semi-sharp while also capturing reasonably sharp stars.
It’s important to ensure the system is balanced carefully – if you are using a lightweight telescope or long lens you’ll want to make sure that you don’t affect the polar alignment when setting up.
If you’re more likely to use heavier lenses, or perhaps a small telescope, then we’d suggest investing in a second counterweight to reduce strain on the gear mechanism.
The maximum capacity is 5kg, with up to 3.5 kg on the counterweight side.
A tension screw can adjust the tension on the gears; the gear switch has to be released when balancing the system, then locked in place for tracking.
Two further locking screws allow the mount head to be freely adjusted in right ascension without affecting the gears.
To test the mount we used our Canon EOS 50D DSLR, which has an APS-C sensor, along with a standard 18-55mm lens and a 100-400mm telephoto lens.
We recorded several images at different exposure lengths to see how well the mount could track: shots longer than 30 minutes could be taken using the small lens set to 18mm, and even when set to 55mm we achieved exposures of 20 minutes with pin-sharp stars.
Larger and therefore heavier lenses push the system more, but we were pleased to be able to capture a 10-minute exposure with only the slightest hint of trailing using our larger telephoto lens set at 100mm.
Overall we were impressed with the capabilities of this mount, especially with the ST4 guide port extending its tracking ability and the fact that it’s portable enough to take with you on holiday to more distant dark skies.
Tracking and guiding
To push the mount’s tracking abilities we set our telephoto zoom lens to 400mm.
As it was long both physically and in focal length this gave a good test of the mount’s stability and tracking.
Through this lens we recorded three-minute exposures, centred on the Ring Nebula in Lyra and the galaxy pair M81 and M82 in Ursa Major, with barely any star trailing.
A bonus is the ST-4 compatible guide port: we used our own autoguiding camera with a 3-inch refractor as a guidescope; this also acted as a counterweight to the 400mm lens.
By guiding we could almost double the length of exposure before any trailing became too obvious.
Aiming at globular cluster M13 in Hercules with 400mm focal length, we managed to get good five-minute exposures while autoguiding; setting the lens at 200mm meant we could achieve 10 minutes with hardly any trailing at all.
The one caveat with this setup is that this mount has no declination adjustment, which may affect the operation of some guiding systems.
Switches and ports
The SkyGuider has a two-way switch to select northern or southern hemisphere use, and a four-way switch to select tracking speed.
There is also an ST-4 compatible guide port, an on-off switch and sockets for power cables for the mount itself and the polarscope’s LED.
Gear switch and tension adjuster
The gear switch engages and disengages the tracking drive mechanism, while the tension adjuster provides control over how firmly the gears are engaged.
This works well, but care is needed when moving the mount head not to loosen the adjuster or turn the gear switch to its unlocked position
The SkyGuider’s built-in illuminated polarscope is one of the best in the field. Its reticule can be used for both northern and southern hemisphere skies, which is useful if you want to take the mount abroad.
The latitude adjustment is sturdy and easy to use.
A wheel at the front allows for fine control as you align Polaris in the illuminated polarscope. Once the latitude is set, it can be locked in place to prevent slippage.
The counterweight shaft can be detached and replaced with a second ball head, making a dual imaging setup.
Alternatively, you could attach a guidescope, allowing for longer exposures to double the amount of data captured per session.
This review originally appeared in the July 2014 issue of BBC Sky at Night Magazine.