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.

Dreaming of a Cave Astrola

Restoring the 8″ Cave Astrola has me again looking at these classic telescopes. Reading the history of Tomas Cave and Cave Optical. Looking at the old advertisements and remembering things long thought forgotten. I may never have owned one before, but the Astrolas still had an impact upon me years ago.

My Astrola is now operational, with final assembly and collimation completed a week ago. So far I have used it for several evening sessions of observing from the driveway. The result is several pages of notes in the observing log, wandering through nebulae, clusters, and binary stars in Orion, Canis Major, and Puppis.

Cave Optical Advertisement 1970
Cave Optical Advertisement 1970, from Phil Harrington
When I was just starting my journey in astronomy the Cave Optical advertisement in each month’s Sky and Telescope was something to inspire dreams in a young teenager. In many ways those dreams have never been forgotten.

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ATM Gallery

Makaʻiki – A 6-inch Travel Telescope

A six-inch f/5 telescope designed to allow maximum portability. A simple travel telescope that can go anywhere, small enough to fit in an airline carry-on bag while leaving room for clothing. Large enough to provide good views of celestial targets.

First Light for Makaʻiki
Makaʻiki under the stars for the first time at Hale Pōhaku on the side of Mauna Kea

I call the design Travel6, for obvious reasons. The actual telescope I have dubbed Makaʻiki, or simply “little eye” in Hawaiian. While 6″ may seem big to some, by the standards of amateur telescopes it is quite small. By the standards of the telescopes I work on it is downright miniscule.

Still, a 6″ telescope is quite capable in the right hands, able to give pleasing views of many celestial objects. The design is an RFT, or rich field telescope. A low power, wide angle eyepiece will result in a field rich in stars.

Like all good telescopes the design is based on ideas borrowed from other telescopes I have seen. In this case the basic design is from a very similar telescope by Brett Schaerer he named WikiKea, a telescope I had a chance to examine at Oregon Star Party a couple years ago. He incorporated a clever focus mechanism into that ‘scope that got my attention. This is a design I liked, I would have to build one for myself sometime.

Travel6 Telescope Plans

Of course I had no plans for the ‘scope, just a couple photos. The first task was to draw up a complete set of plans, only then would I be able to understand all of the design issues. I have posted the full mechanical plans for the telescope at the link above. These plans should be enough for anyone with a little workshop savvy to duplicate the telescope.

The design shown could be notably simplified if one chose to do so. I have enough parts left over to build a second scope, and may consider a refined design the second time through based on the lessons of the first pass.

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Primero

Every astronomer has a first telescope, mine is a 6″ f/5.1 Newtonian I first built as a teenager. As life progressed I was forced to dismantle the telescope and it dwelt for a time as a pile of parts in a box. Eventually I had an opportunity to rebuild the telescope, but as both my technical capability and my financial means had increased I was able to do a substantially better job.

Primero
Primero setup at TIMPA outside of Tucson
The result is the instrument you see to the right, Primero, or simply ‘first’ in Spanish. The original mirror was used but little else from that first telescope was reused. A completely new mount, a new tube and all new fittings. The only purchased parts are the focuser, the Telrad and the secondary mirror. Several parts of the mount were removed and reworked from a previous mount, this includes both the bearings, shafts, counterweight and saddle. The entire tripod, tube, mirror cell, spider and secondary holder were produced by hand for this scope.

The optical design of the telescope is standard Newtonian with a f/5.1 primary mirror of 6.0 inches giving a focal length of 777mm. The mirror was hand ground when I was a teenager and thanks to expert help during figuring is an excellent mirror.

The RFT design is deliberate and has proven to be a good choice, particularly with modern eyepieces that perform so well in short focal length scopes. With a 35mm Tele-Vue Panoptic eyepiece the scope provides a 22x image with just over a three degree field.

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