Category: Astronomical Equipment

This post features all the DIY modifications I have made with a Vixen R114 Newtonian reflector on a Grand Polaris equatorial mount.

Buying a Telescope in the Philippines
Acquiring a telescope for astrophotography may be very costly if it is to be purchased brand new, with prices usually costing (in the Philippines) more than 35,000 pesos (more than $700) for the telescope and mount only, cameras not included. For an aspiring astronomy enthusiast, a low-cost alternative would be to purchase one from a local surplus store. Such stores are popular in the Philippines, selling relatively low-cost second-hand telescopes in good condition, mostly imported from Japan. A few months ago, I purchased a Vixen Newtonian reflector (year 1990, model Vixen R114) with 114 mm diameter 900 mm focal length, on a non-motorized equatorial mount. This telescope was initially purchased by a fellow astro-enthusiast but was offered to me instead for 7,500 pesos ($150) when it was discovered that the telescope has to be repaired as it could not reach focus. I found out later that the optical elements were not properly installed. The telescope does not have a tracker, and thus, is not equipped for deep-sky astrophotography (such as for taking images of galaxies, nebula, and star clusters).

Importance of a Tracking Mount
As the Earth rotates, the apparent position of sky objects changes. Pointing with a telescope would have been easy if sky objects are stationary. But the Sun, planets, stars, galaxies, and nebulae, they all move across the sky at a rate of about 15 deg per hour from east to west. To follow a moving target, the telescope uses motors and controllers that move the telescope at a very precise rate in order to keep an object centered. A tracking mechanism compensates for the Earth’s rotation by moving the telescope just right to negate the effects of Earth’s movement. This capability of a telescope to track is what makes it suitable for taking long-exposure images, a basic requirement in astrophotography.

Building a DIY Go-To Telescope Controller
Telescopes on equatorial mounts without trackers may still follow objects manually by rotating the RA fine adjustment knob. To be useful in astrophotography, tracking must be done with precision. Telescopes with trackers are available, but are costly. An alternative would be to build a tracker using parts that can be purchased online or taken from old appliances (such as printers). There are various open-source projects on the internet about building trackers, one of which is a system called OnStep (which stands for On Cue, On Step). It allows not only tracking but also automated finding of objects in the sky. It can be installed on any telescope, even on a year 1990 model Vixen R114 that I have purchased.

In my particular OnStep build, I used an Arduino Mega 2560 as the main controller board as I am already familiar with it. I also used a pair of LV8729 stepper motor driver and an HC-05 Bluetooth module. For the motor drive mechanism, I used a pulley-and belt system.

I used a pair of 200-step-per-revolution stepper motors paired with 60-teeth and 16-teeth pulley and belt drive system to motorize the Vixen Great Polaris mount with 144:1 worm drive. In this configuration, the total steps are 200 steps * 60/16 reduction * 144/1 teeth worm drive = 108,000 steps per 360 degrees at full stepping. Actual testing showed that accurate tracking is possible at 1/64 microsteps (60 second unguided exposures at 900 mm focal length) . This brings the total steps per revolution to 6, 912, 000 per 360 degrees, or 19,200 per degree (you need to configure this in the OnStep code).

The OnStep telescope controller can be connected to an Android smartphone (using the app OnStep) via bluetooth connection or to a laptop computer via USB connection, running the software Nighttime Imaging N’ Astronomy (NINA) to enable automatic slewing to targets. It also connects with Stellarium to display real-time the telescope’s current position. It uses plate-solving (with ASTAP) to validate and refine its pointing accuracy.

During start-up, the telescope begins with the alignment process in which it will point to a star and ask you to validate that the correct star is shown on the screen or eyepiece. Once successful, the telescope will be capable of finding almost any sky target such as planets, galaxies, and nebulae. The telescope will have very accurate pointing and tracking if properly polar-aligned.

Attaching a Motor to the Focuser
Precise focus is essential in capturing sharp images. Focusing is done by moving the draw tube that holds the eyepiece or camera. This is usually done by looking at the eyepiece or screen to assess focus while rotating the focuser knob. A motor may be attached to the focuser knob to automate this process. Precise focusing can be done by manually operating the controls and stopping when the view is sharp, or by using a software to check proper focus. The software will move the motor and stop at the position where there is good contrast and pinpoint stars. In the Vixen R114, I attached a motor on the focuser and use an Arduino Uno and an A4988 stepper motor driver to control it. The focuser is ASCOM compliant and works with astronomy software such as NINA for remote and automated focusing.

Using Laser as Finder

The telescope comes with a 6 by 30 mm finder scope which is adequate for pointing at bright targets. To add to it, I also installed a laser pointer as a tool for locating objects. The laser pointer is mounted on a spare finder scope holder with collimation screws to enable alignment with the telescope. It has a toggle switch that allows the laser to be turned on and off. To find an object such as a galaxy or nebula, I turn the laser on and point the telescope to the target’s approximate location as indicated in a star map. I then use a pair of binoculars to spot the target. Since the laser allows me to know precisely where the telescope is pointed at, I could use it to guide the telescope to the target. Observe safety precautions when using laser pointers (also, laser pointers are usually not allowed in star parties!)

Installing a Polar Scope
Most second-hand telescopes do not come with complete accessories. The mount the Vixen R114 came with (Vixen GP mount) does not have a polar finder scope. Polar finder scopes help in precise alignment of the equatorial mount’s RA axis with the Earth axis of rotation. I do happen to have a polar scope from a smaller mount that I no longer use. I transferred the polar scope from the other mount into the Vixen GP mount. The polar scope has three centering screws which is needed for calibrating the polar scope’s star map with the actual position of Polaris in the sky. I have tested the polar scope and it works well.

Preventing Collisions with a Pier Extension
Automated telescopes must be able to point anywhere in the sky without the risk of collision between the telescope and the tripod legs. One solution to this is to elevate the telescope on to a pier. Pier extensions can be purchased, but I opted to build one since it is not difficult to do and I happen to have the parts needed. I used three L-bars to lift the tripod head. The pier extension allows unattended imaging without the risk of damage due to collision, to the mount or telescope.

Home-brewing Astronomical Equipment
You will learn many things as you engage more with home-brewed projects. Do not be afraid to modify or improve your existing equipment. Building equipment does not necessarily mean low-cost though, it can sometimes be costly and there is always a risk of damage to equipment. Building DIY equipment, however, can be a worthwhile activity for astronomy enthusiasts. If you want to learn more about improvised astronomical equipment that you can build at home, you may check out my other home-brewed projects here.

Related link: DIY Astronomical Projects

Night Sky in Focus | Astronomy and Amateur Radio
© Anthony Urbano | Manila, Philippines