Night Sky in Focus

Most entry-level telescopes with equatorial mount do not have a built-in clock drive. Due to the absence of a tracking mechanism, these telescopes cannot be used for deep-sky photography. Taking images of galaxies, nebula, and globular clusters as well as faint objects like comets may require exposure time ranging from a few seconds to a few minutes. Without tracking, it is simply impossible to take photos of even the brightest deep-sky objects.

To address this problem, most amateur astronomers tend to improvise by constructing home-built clock drives (or motor drives). One example of such device is shown below: a clock drive made from parts of an old dot-matrix printer, a gearbox from a geared dynamo, a few fabricated metal parts, and a circuit diagram to control the motor.

EtenyTracker2 (left) and its hand controller (right)

The clock drive shown can be attached to any equatorial mount through the RA fine adjustment knob. It is driven by a stepper motor, a kind of motor found in electronic devices that require precise motion control such as hard drives, scanners, and printers. The stepper is controlled by a microcontroller, a circuit that tells the number of the turns it should make every minute (revolutions per minute or RPM) and the direction of its rotation (clockwise or counterclockwise). The schematic diagram was based primarily on the original works of Mr. Rob Paisley. In order to adapt the circuit to the requirements of my telescope, I removed the unused parts of the circuit and added a number of components as well.

If more precise tracking is required, the whole setup can be connected to a computer through the parallel port and an interface can also be constructed to equip the tracker with autoguiding capabilities using an autoguider software like GuideDog and Guidemaster (note that an autoguider setup would require additional equipment like guidescope, web camera, and a computer).

The gearbox (left), stepper motor (upper right), and microcontroller circuit (lower right)

During the clock drive’s initial testing, a relatively bright deep-sky object was chosen, M42, or the Great Orion Nebula. To capture M42 using a 6-inch telescope, it must be tracked for at least 60 seconds. The mount must be perfectly leveled and polar-aligned, and most importantly, the telescope’s clock drive must be calibrated to match the rate of the Earth’s rotation. The image below shows the result of the initial testing. Tracking is unguided.

An improvised clock drive was used to produce this first-light image of the Great Orion Nebula. Tracking is unguided.

Here’s a more recent image of the Orion Nebula (November 2012), taken with a different mount and a different telescope, but still using the same stepper motor controller. Imaged with a  4-inch f/9 refractor and a Kenko NES mount.  Tracking is guided.

A similar clock drive can be built in a few days, with all parts obtained and fabricated locally. The setup can also be adapted for barn-door trackers and equatorial platforms. For queries regarding the project, please leave a comment. Clear skies!

Related page: DIY Astronomy Equipment

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© Anthony Urbano (Manila, Philippines)