DIY Microfocuser for a Telephoto Lens

I’ve built an electronic automatic focuser (EAF) for my Tamron 80 to 210 mm telephoto (zoom) lens for automated and precise focusing. The focuser was built with a stepper motor, an A4988 stepper motor driver, an Arduino Uno, and a repurposed azimuth adjustment mechanism of an old Vixen mount.

DIY microfocuser for a telephoto lens

Vixen’s alt-az mount azimuth lock mechanism happens to be wide enough to fit a telephoto lens. It allows fine movement using the fine adjustment knob attached to a stepper motor with 60:16 pulley and belt system. It features a clutch mechanism that allows for manual focusing. The lens and the camera are held in place with mounting rings from an old 80 mm Vixen refractor. An aluminum baseplate is used to mount together as a unit the lens, camera, focuser, finder scope, and guide scope. The controller for the focuser was housed in a project box. A dovetail bar connects the whole assembly to the telescope mount.

I have tested the focuser on several imaging runs now and it appears to be working fine, especially with wide-field targets such as the Lagoon and Veil Nebula. To watch a video showing the microfocuser in action, click here

Related links:
DIY Electronic Automatic Focuser (EAF) | Refractor
DIY Electronic Automatic Focuser (EAF) | Reflector

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

DIY Polar Scope for Vixen GP Mount

I have installed a Kenko polar scope to a Vixen Great Polaris (GP) mount. I modified the polar scope’s coupler to fit the Vixen GP mount. Instead of the standard threaded coupling, I used three screws to attach the polar scope onto the mount. A separate set of centering screws allow alignment of the star map overlay with that of the actual stars in the sky.

Kenko polar scope to a Vixen Great Polaris (GP) mount

A polar scopes is helpful in aligning the mount’s polar axis with that of the Earth’s axis of rotation, but it lacks the precision required for astrophotography. When imaging at longer focal lengths, I recommend not relying on a polar scope, but instead use the declination drift alignment method for polar alignment. It looks at two stars, one in the eastern or western horizon, and another in the celestial equator, allowing for better polar alignment even without the view of Polaris.

Star chart from a 1990 polar scope still works!

Related link: Kenko NES Mount

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

DIY Upgrades for a Newtonian Reflector

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).

Vixen R114 on a modified Vixen Great Polaris mount

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.

OnStep Telescope Controller

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.

OnStep with Smart Hand Controller

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).

OnStep Telescope Controller

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.

Right-Ascension Motor
Declination Motor

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.

Unguided 60 sec exposures at 900 mm with an OnStep-controlled mount, Dumbbell Nebula (1 hour)

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.

DIY Electronic Automatic Focuser installed on a Vixen R114

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!)

A laser pointer attached to a telescope allows easy star-alignment for an accurate go-to system

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.

Polar scope upgrade
1990 star chart reticle still works

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.

DIY pier extension

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.

Trifid Nebula imaged with a Vixen R114 on Vixen GP mount with home-brewed tracking system

Related link: DIY Astronomical Projects

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

DIY Pier Extension for EQ Mount

I have built a DIY pier extension to allow my DIY go-to telescope to move without hitting the tripod legs. It consists of three 12-inch L-bars (which I later shortened to 7.5 inches, after measuring the minimum clearance required) that lift the tripod head. I repurposed a tripod head from an old and unused tripod to serve as the base where the L-bars and the tripod legs connect to. The pier extension allows unattended imaging without the risk of damage to the mount or telescope.

DIY Pier Extension

To watch a video of the telescope performing a successful meridian flip without hitting the tripod legs, click here.

Related link: Converting the Vixen Great Polaris mount into a Go-to mount

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

DIY Telescope Controller | OnStep

I have built a controller for my Vixen Great Polaris mount using the OnStep go-to telescope controller. I used an Arduino Mega 2560 as the main controller board, a pair of LV8729 stepper motor driver, and an HC-05 bluetooth module (which connects to the OnStep Android app).

I also built a Smart Hand Controller (SHC) using an ESP32 module, an OLED display, and a button array. The SHC connects to the same serial communication lines (Rx and TX pins) used by the HC-05 bluetooth module. I use a toggle switch to select between the HC-05 Bluetooth module for the Android controller and the Smart Hand Controller with ESP32 module.

OnStep Telescope Controller

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 even at just 1/64 microsteps (as evident in a 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 these values in the OnStep code.

The OnStep telescope controller can be connected to NINA to enable automatic slewing to targets and use plate-solving to validate and refine its pointing accuracy. It also connects with Stellarium to display real-time the telescope’s current position.

Unguided 60 sec exposures at 900 mm with an OnStep-controlled mount, Dumbbell Nebula (1 hour)

OnStep will have very accurate pointing and tracking even with just one-star alignment, if properly polar-aligned.

OnStep Telescope Controller


Related links:
Trifid Nebula imaged with the OnStep DIY Go-to Controller
OnStep Main Page
Smart Hand Controller Main Page
Schematic Diagram OnStep Main Board and Smart Hand Controller

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

Vixen R114 on Great Polaris Mount

I have recently acquired a Vixen R114 Newtonian reflector (114 mm aperture, 900 mm focal length at f/7.9) on a Great Polaris equatorial mount. The mount does not have motors, but I have converted it into a fully-automated go-to and tracking mount capable of unguided exposures of at least 60 seconds (field-tested without guiding).

Vixen R114 on Great Polaris Mount

The reflector has a very good primary and secondary mirror cells which allowed precise collimation and prevent strained optics. The stock focuser is a 0.965 in barrel which I modified and converted to the 1.25 in standard. The rack-and-pinion focusing mechanism is very precise and sturdy enough to hold an ASI 533 astronomy camera even without using the focuser lock. It comes with a 6 x 30 mm finder which is adequate for pointing at bright targets.

Trifid Nebula M20, 1.7 hours exposure

The Vixen R114 on Great Polaris equatorial mount now serves as my long focal length telescope both for visual observation and imaging.

Related links:
Converting the Vixen Great Polaris mount into a Go-to mount
DIY Upgrades for a Vixen R114 on GP mount
Sky-Watcher Equinox 100ED

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

Laser Pointer as Finder

I have installed a laser pointer to my telescope as a tool for locating objects. The laser pointer is mounted on a 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.

Using laser pointer as a finder

To find an object such as a galaxy or a nebula, I turn the laser on and point the telescope to the target’s approximate location as indicated in a star map. If the target is too dim and there are no bright stars in the vicinity, I just use a pair of binoculars to spot the target and then slew the telescope manually to the target. The laser allows me to know precisely where the telescope is pointed at, and then use the laser to guide the telescope to the target. Observe safety precautions when using laser pointers.

To view posts on DIY projects and astronomical equipment, click here.

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


DIY 40 m, 20 m, 15 m HF Dipole

I have built a multi-band DIY fan-dipole antenna for 40-meter, 20-meter, and 15-meter HF bands. A fan dipole consists of several dipoles fed at a common feed point, through an optional 1:1 balun. I have tested this antenna and I have confirmed QSOs from Philippines to Brazil (other side of the world from the Philippines, via FT8 on 15 meters) and Philippines to Sydney, Australia (SSB voice on 15 meters).

A fan dipole may be designed to operate on a number of bands simply by adding new elements to an already existing dipole, but adding new elements may change the tuning of the already tuned dipoles, making it difficult to build one that is designed to operate on too many bands. In this particular antenna build, I combined three dipoles—for 40 meters, 20 meters, and 15 meters—to form a multi-band fan dipole on a single feedline.

DIY Fan-Dipole Antenna


The driven elements are 12-gauge insulated wires, center-fed (split in the middle). I used a 7 meter RG8 coaxial cable feedline with 1:1 BU-50 balun. The feed point is housed in a weatherproof metal enclosure that has been placed on an elevated concrete ledge. I used non-metallic material to raise and anchor the ends of the wires, such as nylon rope.

The 40 meter band has 10 meters of wire on each sides (total of 20 meters both sides), the 20 meter band has 5 meters of wire on each side (total of 10 meters), while the 15 meter band has 3.38 meters of wire on each side (total of 6.77 meters). Adjust the lengths of the elements for lowest SWR on the desired operating frequency. Since there is likely interaction between the elements, always check the tuning of all the other bands when tuning the antenna for a specific band.

To view all posts about amateur radio, click here.

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


DIY Dual-Band VHF-UHF Dipole

I have built a DIY dipole antenna for VHF (2 meter) and UHF (70 cm ) bands. I used 1/4 in diameter copper tube elements. The VHF driven element is center-fed while the UHF element is coupled (placed in close proximity but not connected to the coaxial cable) with the VHF driven element. A 5 meter RG8 coaxial cable feedline is used, with no balun. The feed point is housed in a weatherproof plastic enclosure, with one side of the VHF dipole connects to the coaxial cable’s center conductor and the other side connected to the outer conductor.

DIY VHF-UHF antenna

In this particular antenna, the VHF element has a total length of 984 mm (split in the center, to form two 1/4 wavelength element with 492 mm on each side) and the UHF element is 325 mm (1/2 wavelength element, not split in the middle). Adjust the lengths of the VHF and UHF elements for lowest SWR on the desired operating frequency.

To view all posts about amateur radio, click here.

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


FT8 and other digital modes with ICOM 718

I have built a DIY interface for my ICOM 718 HF radio to send and receive audio signals to a laptop computer and control the PTT keying, for use with various digital modes such as FT8. I used a USB sound card for the audio interface, and a USB-to-serial port adapter for PPT keying.

FT8 with Icom 718

The audio output of ICOM 718 (from speaker out or Pin 12 in the accessories port) connects to the microphone in of the sound card (pink port, microphone port). The audio output of the sound card (green port, headphones port) connects to Pin 11 of the ICOM 718’s accessories port. The USB-to-serial port is then configured in the settings tab of the software WSJT-X to send pulses to the the serial port’s RTS pin, which then controls a BC547 transistor to key the PTT (Pin 3 in ICOM 718’s accessories port) when transmitting a signal.

DIY USB soundcard interface

The circuit board of the USB sound card and the USB-to-serial adapter are then removed from their housing and soldered directly on to a USB hub. This configuration allows both modules to work with just one USB port of the laptop. I then put everything inside the metal casing of the radio, in a section protected from radio interference. To operate in digital modes, I only need to connect one USB cable from the radio.

During my initial tests, I was able to contact a station in Brazil (South America), from the Philippines, at 21.074 MHz (15 meters), using a 40-meter band center-fed dipole wire antenna resonant to the 15-meter band.

To view all posts about amateur radio, click here.

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


Sky-Watcher Equinox 100 ED

The 2011 Sky-Watcher Equinox 100 ED 4 in f/9 refractor serves as one of my main telescope both for visual observation and astrophotography. The Optical Tube Assembly (OTA) features a 4-in f/9 extra-low dispersion (ED) apochromatic (APO) lens design. It has a 2-inch dual-speed Crayford focuser with a thumbscrew underneath for locking the draw tube. The telescope comes with aluminum-lined wooden carrying case. It is supplied with two eyepieces: 25 mm and 5 mm. Supplied also is a 90-degree 2-inch diagonal mirror and an 8 by 50 finder scope.

In 2021, the telescope has been modified and fitted with a DIY reducer, making the telescope faster (from f/9 to f/5.65, at 0.63x ) and also reducing the tube length by 20 cm.

To view images taken with this telescope, click here.

Related link: Vixen R114 Newtonian Reflector

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