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

Automated Station ID with ISD1820

The ISD1820 is a sound recorder and playback module capable of storing 20-second audio recordings. It features the ability to initiate playback with a button press or a pulse, which is very useful in automated transmissions. The playback signal can be generated manually by tapping the playback button onto a radio’s PTT button, or by using a dedicated controller (such as a timer or an Arduino) for sending transmissions at regular intervals. To send the module’s audio signal to a radio transmitter such as a VHF radio on FM mode or an HF radio on SSB, connect the speaker out to the microphone line input of the radio. This module can be used to send repeated transmissions such as station IDs or for calling a CQ.

ISD1820 is sound recorder and playback module

To view all posts about amateur radio, click here.

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© 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 Tamron to Astrocam Adapter

I have a 1980 Tamron 80 mm to 210 mm telephoto (zoom) lens that I intend to use for astrophotography. I could not find a dedicated astro camera adapter for this particular lens so I just improvised one. I used epoxy to connect a Tamron to Canon EOS adapter and an M42 connector for my ASI 533 astro camera.

After several imaging sessions with the Lagoon and Veil Nebula, the DIY adapter appears to work.

Related links:
Universal Camera Adapter
DSLR to Telescope Adapter

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© Anthony Urbano | Manila, Philippines

DIY Electronic Focuser | Reflector

I’ve built an electronic automatic focuser (EAF) for my Vixen R114 reflector for automated and precise focusing. The focuser was built with a geared stepper motor, A4988 stepper motor driver, and an Arduino Uno.

DIY Electronic Focuser for a Vixen R114 reflector

The focuser is ASCOM compliant and works with astronomy software such as the Nighttime Imaging N Astronomy (NINA) for automated focusing during unattended imaging. To watch a video showing the focuser’s movement, click here.

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

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

DIY Ultra-Portable Sky Tracker

Due to Earth’s rotation, objects in the sky appear to move from east to west. Taking a long-exposure photo of stars using a camera on a non-tracking mount will produce trails. To compensate for the Earth’s rotation, a tracker as simple as a geared stepper motor can be used. This tracker is controller by a simple Arduino-based stepper controller.

18 mm at 90 sec (animation)
Milky Way captured with an 18 mm lens at 90 seconds exposure, with and without tracking.

Any geared stepper motor with sufficient torque can be used as a drive mechanism. For this project, I used a stepper motor with a built-in 1:500 gearbox.

Ultra-portable tracker for DSLR cameras

I simply attached an aluminum plate to the end shaft of the stepper. A ball head mount was then used to connect a DSLR to the plate. All the components can fit easily in a small camera bag. It is designed to carry only a very light payload such as a DSLR with a wide-field lens.

Component parts of the DIY portable tracker

To test it further, I also tried it with a more demanding lens: 55 mm. Without tracking, stars appear as streaks, but with tracking, stars remain as fixed points.

55 mm at 120 sec (animation)
Milky Way captured with a 55 mm lens at 120 seconds exposure, with and without tracking.

Even with a 55 mm lens, the tracker is capable of accurate tracking up to 120 seconds, which should be accurate enough for Milky Way shots.

Calibrating the DIY Tracker

The tracker’s ‘tracking speed’ needs to match the actual movement of the sky. Calibrate your own tracker by making sure that the stepper does not rotate a bit too fast nor too slow. Align the tracker’s axis of rotation (or what is called the polar axis, which in this case, the stepper’s main shaft) with the north star Polaris (for observers in the southern hemisphere, point the tracker’s polar axis in the general direction of the Earth’s southern polar axis). Point the camera to any bright star. Turn the tracker on and start tracking the sky. Take a series of shots (with just enough exposure to capture the position of stars). By looking at the live view images or photos taken, you should be able to tell whether or not the tracker is moving too fast or too slow.

Polar Alignment

Before attempting this method, make sure that you have already calibrated the tracker, that is, you’ve managed to achieve a correct tracking rate. When pointed to a star in the east, minimize the north-south drift by adjusting the polar axis higher or lower (altitude adjustment). When pointed to a star in the celestial equator (near meridian), minimize the north-south drift by adjusting the polar axis to the left or to the right (azimuth adjustment). The east-west drift is corrected by adjusting the tracker’s speed.

This project has been featured in HACKADAY.

Related links:
DIY Telescope Clock Drive
DIY OnStep Go-To Telescope Controller
View all home-brewed DIY astronomy equipment

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© Anthony Urbano | Manila, Philippines

DIY Telescope Clock Drive

Clock drives are simple tracking mechanism that move a telescope’s RA axis one rotation every one sidereal day (23 hours and 56 minutes) to effectively compensate for the Earth’s rotation. It allows precise tracking of planets, galaxies, nebula, and other sky targets.

Telescope clock drive controller based on L293D and Arduino Uno board

An inexpensive Arduino Uno board and L293D-based stepper motor driver can be used to control a telescope. Attach a stepper motor on a telescope’s RA adjustment knob, then find the correct motor speed that will match the movement of the sky. Below is a sample sketch for a simple telescope clock drive controller.

//Simple clock drive controller by Anthony Urbano 06 September 2021. It uses an Arduino Uno and an L293D.

#include <AFMotor.h>                  //Go to SKETCH > INCLUDE LIBRARY > then lookup "Adafruit Motor Shield Library"
AF_Stepper motor1RA(24, 1);           //Initializing motor's steps per one full rotation; Connect the motor to M1 port
void setup() 
{
}

void loop()
{
  motor1RA.setSpeed(100);              //Change the value to speed up or slow down the tracker
  motor1RA.step(1, FORWARD, DOUBLE);   //Motor takes 1 step forward; to reverse direction, replace FORWARD with BACKWARD
}
 

With proper polar alignment, a simple clock drive is capable of imaging deep-sky objects, such as the Flame and Horsehead Nebula. This image was captured with a telescope at 565 mm focal length.

Flame & Horsehead Nebula imaged with a telescope mount with a simple clock drive mechanism

Related links:
OnStep Go-To Telescope Controller
View all home-brewed DIY astronomy equipment

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© Anthony Urbano | Manila, Philippines

Modified Celestron Travel Scope 70

The Celestron Travel Scope 70 has a front lens diameter of 70 mm and a focal length of 400 mm. A telescope with these specifications works well for terrestrials observations, both for daytime and nighttime.

Celestron Travel Scope 70 with modified focuser, upgraded tripod and accessories

Due to its size, however, it has a very limited use for astronomical observation. Note that the telescope showed signs of chromatic aberration, like any other low cost telescopes.

Moon imaged with a Celestron Travel Scope 70, an ASI 533 astronomy camera, and a Vixen GP tracking mount
Lagoon Nebula M8 imaged with a Celestron Travel Scope 70, an ASI 533 astronomy camera, and a Vixen GP tracking mount
Eastern Veil Nebula imaged with a Celestron Travel Scope 70, an ASI 533 astronomy camera, and a Vixen GP tracking mount
Helix Nebula imaged with a Celestron Travel Scope 70, an ASI 533 astronomy camera, and a Vixen GP tracking mount

Related links:
Portable Telescope Setup
View all home-brewed DIY astronomy equipment

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© Anthony Urbano | Manila, Philippines

DIY Universal Camera Adapter

A universal camera adapter allows any camera to be attached to a telescope or binoculars. This imaging method is called afocal imaging, in which a camera with its lens is mounted next to another image-forming optical system such as a telescope or a pair of binoculars. This adapter was built in 2008 and still in use today.

A universal camera adapter for connecting any camera with any telescope

Related link: Smart Phone-to-Telescope Adapter

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DSLR to Telescope Adapter

A T-ring is a metal adapter with one end that fits on a lens mount and with the other end that connects to a T-adapter. Each camera brand has it’s own T-ring design. The T-adapter connects any T-ring to a telescope.

The Canon EOS T-ring shown in this setup is produced by Celestron, while the T-adapter was fabricated in a machine shop. Some telescopes have threaded focusers that may accept a T-ring directly, thus, eliminating the need for a T-adapter.

Related link: View all home-brewed DIY astronomy equipment

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© Anthony Urbano | Manila, Philippines

DIY Field Battery

Over the years, I have used various types of batteries, but the one I use most often is the deep-discharge lead-acid type. They are robust, low-cost, can be charged with almost any compatible power supply, and most importantly, can double as a vehicle jump-start kit when not being used in the field. I use four 12V 9Ah deep-discharge lead acid batteries connected in parallel, to power the laptop, and another 12V 9Ah battery for the telescope’s tracker. These batteries remain usable for 2 to 3 years.

A modular field-battery to power my equipment during remote imaging sessions

A moderately-sized field battery has more than enough power to last an overnight imaging session.

Related link: View all home-brewed DIY astronomy equipment

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© 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

Portable Telescope Setup

I have a TravelScope70 which has served as a guide scope for my imaging setup for many years. Now that I have shifted to an off-axis guider (OAG) setup, the TravelScope70 is now being repurposed back to a grab-and-go travel light telescope setup, to be used particularly in astronomy outreach events and visual observations.

Aluminum-lined hard case for the Celestron TravelScope70

The TravelScope70 is a good small-aperture low-magnification telescope, if paired with a good diagonal and set of eyepieces. It will show good views of the moon and allow decent moon photography. Due to the short focal length, small aperture, and lack of a dedicated and more robust mount, the TravelScope70 may be limited to moon viewing and other large and bright targets such as star clusters and nebula.

Related link: Celestron Travel Scope 70

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© 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.

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© 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


DIY Projector Lens Telescope

Projectors have lenses that may be used to build low-magnification telescopes. I happen to have found an old 70 mm diameter LCD projector lens with focal length of 105-210 mm which I paired up with an eyepiece to build a DIY telescope.

DIY projector lens telescope

This projector lens, while not designed to be used as a telescope lens, may still provide good views. I measured the proper focus distance and used a DIY adapter to attach a 2-in diagonal mirror and a 40 mm lens to it. This combination produced a 2.6 by 70 to 5.25 by 70 finder scope (wide field of view with ability to zoom). Focusing is done by sliding the eyepiece in and out of the diagonal’s eyepiece holder. I then made an improvised reticle (cross hair) to finally complete the setup. I will be using this DIY projector lens telescope in star-hopping to deep-sky targets and scanning large areas of the sky.

Related link: View all home-brewed DIY astronomy equipment

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© Anthony Urbano | Manila, Philippines

DIY Focal Reducer

I have built a DIY focal length reducer (focal reducer) by inserting a converging lens from an old telescope along the optical system of a Sky-Watcher Equinox 100ED . The telescope’s native focal length is 900 mm at f/9. With the DIY reducer, the focal length is reduced to 565 mm at f/5.65 (actual focal length as measured by SIRIL’s plate solver function). The lens used was the objective of a Vixen 80 mm f/11 achromat, reducing the native focal length of my telescope by 0.63x.

DIY Focal Reducer

Focal reducers are optical elements (usually a convex lens or lens group) that converge light from a telescope’s objective. It shortens the focal length and in effect, produces a faster telescope (lower f/ratio) and widens the field of view (larger portion of the sky is seen or captured). Any decent quality converging lens should work as a focal reducer. It works opposite to a Barlow lens which increases the focal length by using a concave lens or diverging lens. Unlike dedicated focal reducers designed to maintain optimal image quality, DIY focal reducers may introduce aberration and must be considered when attempting this modification.

Orion Nebula M42, imaged with the DIY focal reducer

I had to shorten the optical tube by about 200 mm to reach focus, and then reattach the focuser. The focuser’s draw tube was also shortened by 55 mm to prevent it from obstructing the light and stopping down the objective lens when the draw tube moves inward. The telescope’s optical tube has an inner diameter of about 100 mm which has enough space to accommodate the lens cell of the Vixen 80 mm lens. Only the central 60 mm part of the reducer is used due to the presence of a light baffle in the telescope’s optical tube assembly.

Related link: View all home-brewed DIY astronomy equipment

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© Anthony Urbano | Manila, Philippines

DIY Off-Axis Guider (OAG)

I have built a DIY off-axis guider (OAG) using a mirror from a DSLR camera, some tube extenders (2 in and 1.25 in diameter), and a webcam. Best guiding performance currently at 0.33″ (arcsecond) RMS error, at 900 mm focal length, using a mount with DIY controller.

DIY Off-Axis Guider (OAG)

In off-axis guiding, the telescope functions both as an imaging scope and a guide scope. In this configuration, a mirror or a prism receives a portion of the light without blocking the main imaging sensor, sending the light to a guide camera. In this build, I used a high-quality mirror I happen to have found in a non-working Canon 1100D. To build the OAG, I removed the lens from a Barlow so I could get a 1.25 inch barrel for the webcam attachment, and then fastened it perpendicular to a 2 inch extender, where an appropriate side hole has been made. I then fabricated a small mirror mount (like a secondary mirror mount in a Newtonian) using some brass material, to send the reflected light on to the side. The placement of the mirror and the proper spacing to achieve focus required trial-and-error. To use the OAG, focus the main camera first, and then slide the guide camera in or out to achieve focus.

M51 Whirlpool Galaxy, imaged with the DIY Off-Axis Guider

Related link: View all home-brewed DIY astronomy equipment

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© Anthony Urbano | Manila, Philippines