A Universal Afocal Adapter

A couple weeks ago at the volcano I let quite a few folks take imagery of the lava using the afocal technique, simply holding the phone up to the eyepiece. This works rather well as the phone uses a lens much like the human eye, about the same aperture.

Shooting afocal with an iPhone and the TV-76mm 'scope
Shooting afocal with an iPhone and the TV-76mm ‘scope

The only real issue is holding a phone in just the right spot. Folks wanted video, but holding the phone steady is a real challenge. I had thought of making something to do this many times, last weekend I did it.

A session of playing around in 3D CAD resulting in a couple bits of clever plastic printed with the 3D printer… Done.

There are commercial solutions for this available, quite a few actually. But most of these are intended to adapt to a single phone, using some sort of clamping arrangement that you have to setup for a particular phone. I envisioned something that was more universal, quickly adapting to any phone.

The method I chose was a sliding magnetic platform that holds the phone. Just a simple shelf actually, set the phone on it and slide until you get it lined up. The base piece is printed with a recess into which a steel plate is set. The slider has three 8mm x 2mm neodymium magnets to securely grab the steel plate.

It took a bit of work to cut and file the steel plate to neatly fit the base, a bit of inlay work. Otherwise making the piece is quite easy. The only design issue is that this adapter is setup to fit a single eyepiece, a Televue Panoptic 27mm, and cannot be easily adapted to others.

The 3D CAD files are linked below. I have included the SCAD source file to allow tinkering with the design, possibly adapting to a different eyepiece. Both parts should be printed with support on, the pockets for the glued bits will have to be cleaned out, the resulting rough surfaces just right to recieve epoxy.

Afocal adapter 3D CAD files

At the Keanakakoʻi Overlook I was able to test the adapter with a variety of different phones, both iPhone and Android, graciously lent to me for my experimentation. OK, the owners may have wanted a few lava photos. There was no difficulty using the adapter other than a moment or two needed to line up the camera with the exit pupil of the eyepiece. The result was more than a few smiles.

A 3D Printed Finder ‘Scope

I wanted a smaller, lighter finder ‘scope for the Astrola, and I wanted right angle to stop straining my neck!

3D model of the 40mm finder ready for printing
3D model of the 40mm finder designed in OpenSCAD

I have been using a big Orion 9x60mm finder on the Astrola, the only telescopic finder ‘scope I have among the Telrads. It is nice, with a bright image that shows many faint fuzzies. It is also huge, and very heavy, it is also straight through, requiring one to crane your neck around to view through it on the Newtonian ‘scope.

A small, lightweight finder was in order, a perfect project for a newly arrived 3D printer.

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A View from the Past

As an evening pastime in these COVID restricted days I have been delving into the past again. Again reading the work of an amateur astronomer from long ago.

Frontspiece of Bedford Catalogue, 1844
Frontspiece of Bedford Catalogue, 1844, Capt. William Henry Smyth

I had previously read through the work of Rev. Thomas Webb, a vicar and amateur astronomer active in the late 1800’s. Webb frequently referred to the work of an earlier observer, Capt. William Henry Smyth.

Retired British Navy Captain Smyth was a backyard observer, gazing at the stars with a 150mm refractor from a garden behind his home in Bedford England. His telescope was quite good for the time, made by Tully of London, the best money could buy. This telescope was eventually purchased by the British Government to be used in the 1874 transit of Venus expedition to Egypt and the 1882 Venus transit in Jamaica. It now sits in the collection of the Science Museum, London.

Capt. William Henry Smyth's Telescope at Bedford
Capt. William Henry Smyth’s Telescope at Bedford

Smyth published two volumes on astronomy in 1844 under the title A Cycle of Celestial Objects . Volume II of this set, commonly called The Bedford Catalogue, contains descriptions of more than 1600 double stars, clusters, and nebulae, serving as a guide to what may be observed with a small telescope. The Bedford Catalogue became the standard at-the-telescope reference for other amateur observers for many decades until it was generally replaced by Webb’s Objects for Common Telescopes.

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Eyepiece Time

Given stay at home orders and a virus haunting our community I have gotten quite a bit of eyepiece time this year. Mostly quick driveway session in the evening, or sometimes the early dawn hours, a solo activity perfect for social distancing.

At the telescope in the driveway again
At the telescope in the driveway again

I usually use my roll-out scope ready in the corner of the garage, a classic 8″ Cave Astrola. Just roll it into the driveway, plug it in using the purpose located power receptacle on the corner of the lanai,. slide an eyepiece in… Ready to go in two minutes.

Last night was a perfect example… It was raining at sunset, but an hour later the skies were clear and dark. Better yet the rain had left clear, haze free air overhead with great transparency. I spent an hour hunting down dark nebulae in Aquila, dark clouds of galactic dust best visible with perfect skies.

The pages of the observing notebook fill quickly, a page or two each evening until the Moon comes back. I have so many object I have never viewed, so many easily visible from the driveway with a fairly small 8″ ‘scope.

Often I come across pleasant surprises, a pretty binary or a deep red carbon star, the region surrounding my target rich with stars and wisps of nebulae, so many wonders I have never seen despite years at the eyepiece.

Astrophotography from the Driveway

A clear night finally appeared, clouds have been plaguing this particular dark of the Moon. What to do? Maybe do some astrophotography?

The nebula complex M17 in hydrogen-alpha
The nebula complex M17 in hydrogen-alpha

I have a new piece of kit, a ZWO ASI Air Pro that has been on back-order since November. With shutdowns in China and the rest of the mayhem it finally arrived this week.

The unit is a little dedicated astrophotography computer that makes a lot of the setup so much easier, while simplifying the snarl of cables on the telescope.

Controlling the camera, filter wheel, and guiding is done through a very nice app on the iPad. In less than an hour I had the basics figured out and was taking images.

A few technical issues to learn about through the night, such as how to best configure the WiFi for use with the home network, how to access and download the images to the desktop computer, etc., but no real problems. I took images through until dawn’s glow appeared in the data, running from twilight to twilight.