DIY Microfocuser

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 
© Anthony Urbano | Bacoor, 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 attached 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 meridian near 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 
© Anthony Urbano | Bacoor, Philippines

DIY Pier Extension

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 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 
© Anthony Urbano | Bacoor, 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.

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.


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

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© Anthony Urbano | Bacoor, 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
Sky-Watcher Equinox 100ED

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© Anthony Urbano | Bacoor, Philippines

Laser Pointer 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 
© Anthony Urbano | Bacoor, Philippines


Sky-Watcher Equinox 100 ED

The 2011 Sky-Watcher Equinox 100 ED 4 in f/9 refractor serves as one of my main telescopes 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.

Sky-Watcher Equinox 100ED at f/6.28 (100 mm aperture, 628 mm focal length)

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.

Modified Sky-Watcher Equinox 100ED on an improvised telescope hard case.

In 2021, the telescope has been modified and fitted with a DIY reducer, making the telescope shorter and faster (from f/9 to currently at f/6.28, 0.7x ) and also reducing the tube length by 20 cm.

Orion Nebula imaged with a focal reducer at 100 mm aperture, 680 mm focal length (f/6.28)

Related link: Vixen R114 Newtonian Reflector

Night Sky in Focus 
© Anthony Urbano | Bacoor, Philippines