Anyone who has turned a camera to the night sky immediately discovers new rules of photography. True, some cameras have a “starry night” setting requiring the use of a tripod. Typically, this tells the camera to take up to a 15-second exposure. But when you examine the resulting picture, the stars record as tiny hyphens rather than points.
Welcome to the Earth’s rotation. The longer your exposure, beyond 10 seconds or so, the more Earth turns on its axis, and the hyphens soon become trails. Star trails can be artistic, but what most astro-imagers want is realistic pinpoint stars and lots of them.
The solution is an equatorial mount with motorized drive (what used to be called a clock drive) to precisely counteract the Earth’s rotation. In its standard form, the equatorial mount’s polar axis is angled to aim at the north celestial pole, near Polaris, the North Star.
As DSLR cameras have become increasingly capable of amazing night-sky performances, the idea of a highly portable equatorial mount for such cameras has come of age. The latest entry in this category is the iOptron SkyTracker, for use on a solid camera tripod. For this review, iOptron loaned us a unit from stock.
The SkyTracker requires a ball-head mount, a common camera accessory, to allow the camera to be locked in any direction while being guided on the sky (the ball head is shown at upper right between the camera and the aluminum drive head on the tracker). Apart from that, the SkyTracker is entirely self-contained, making it ideal for the travelling astronomer.
The tracker has a payload capacity of three kilograms, so it can double as an equatorial mount for a travel telescope such as a 60mm to 70mm apo refractor that can be fitted on the ball head.
One of the best features of this product is the polar-alignment scope provided with the unit that slides into a dedicated socket and is secured by a thumbscrew. The reticle in the polar scope is cleverly illuminated by a red LED in the tracker socket. Using the Polaris offset ring, I was able to quickly align the tracker with enough accuracy for 6-minute exposures with a 35mm lens.
The Polaris offset technique I use is to place Polaris on the 40′ reticle ring at the same angle that Kochab, the brightest star in the Little Dipper’s handle, is in the naked-eye sky. With practice, this can be done with both eyes open, one looking at the real sky, the other through the polar scope.
Priced at $400, the iOptron SkyTracker comes with a user manual and a soft carry case. This solid, well-designed tracking mount can open new astrophotographic possibilities for you and your DSLR camera. Highly recommended.
