I have built a lightweight portable DIY star tracker for DSLRs. It uses a worm drive from an unused equatorial mount I have found in a local surplus shop. I used a geared stepper motor and an Arduino controller to spin the RA axis at the correct tracking rate to match the apparent movement of the sky. The setup was housed in a metal box that fits in a small camera bag. It mounts on a standard camera tripod. I have tested it to track accurately with a DSLR with an 80 mm to 210 mm 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.
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.
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.
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 meridian near the celestial equator, allowing for better polar alignment even without the view of Polaris.
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.
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.
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.
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.
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.
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.
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.
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 reveal 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.
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.
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.
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
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 taken with a telescope at 565 mm focal length.
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.
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.
In 2021, the objective lens of this telescope has been repurposed as a DIY focal reducer.
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 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.
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 moderately-sized field battery has more than enough power to last an overnight imaging session.
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.
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.
OnStep will have very accurate pointing and tracking even with just one-star alignment, if properly polar-aligned.
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.
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.
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.
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.
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.
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.
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 628 mm at f/6.28 using the objective lens of a Vixen 80 mm f/11 achromat.
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 imaged). Any decent quality converging lens should work as a focal reducer (in this use case, a lens from a telescope I no longer use). It works opposite to a Barlow lens which increases the focal length by using a concave lens or diverging lens. DIY focal reducers may introduce aberration and must be considered when attempting this modification.
To reach focus, I had to shorten the optical tube by about 200 mm, 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 various lenses. Only the central 60 mm part of the reducer is used to refract the light cone due to the presence of a light baffle in the telescope’s optical tube assembly.
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.
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.
Using a gearbox from an electronic screw driver and a stepper motor from a printer, I’ve built a declination motor drive (direct drive and using gearbox).
The electronic screw driver has a DC motor which I removed and swapped with an old printer’s stepper motor. The gearbox attaches to the declination worm screw using an improvised coupler. I designed it to feature a clutch knob to disengage the motor drive in case I need to slew manually, using the fine adjustment knob.
The stepper motor is driven with an A4988 stepper motor driver board and controlled with an Arduino Uno microcontroller. Two push buttons are used to slew the telescope north or south. I had to perform a field test in order to correctly set the motor’s speed to match the slew speed of the RA motor. The declination motor can be used for declination guiding. I have also tested it to work with a DIY go-to controller.
Equatorial telescopes near the equator have polar axis with very low elevation and as a result, the counterweights may hit one of the tripod legs. With this new set of DIY counterweights, I was able to reposition the weights just enough distance to clear the north-side tripod leg, while at the same time, shift the weights closer to the polar axis, making the whole system more stable.
When imaging targets using a DSLR lens, achieving proper focus may be difficult even when using a Bahtinov mask. Focus adjustments involving very small and precise steps can be achieved using a microfocusing mechanism. In this DIY project, I have modified a Canon 50 mm f/1.8 lens and tapped onto its built in electronic microfocuser. It uses an L293D stepper motor driver and an Arduino Uno.
The focuser is ASCOM compliant and works with astronomy software such as the Nighttime Imaging N Astronomy (NINA) for automated focusing during unattended imaging. The modification should work with any lens with built in electronic focusers.