Living in the islands provides excellent observing for an amateur astronomer such as myself, but there are drawbacks. I do miss the large star parties, getting together with hundreds of other observers to see other telescope setups, to learn, and to share the sky.
The 10″ f/4.5 travel scope Holoholo
Thus I have made a habit of traveling to the mainland once in a while to attend one of the larger star parties. This year I will again attend Oregon Star Party. It has been a while, the last time was 2017, the year of the total solar eclipse.
Traveling from the islands to a star party makes it a challenge to bring a large telescope. Last time I borrowed an 11”, not a bad solution, it worked, but it was not my ‘scope. This time I was determined to realize a long considered idea, to build a substantially sized travel telescope. Thus Holoholo was designed and built, a 10.1” f/4.5 travel ‘scope.
This has been a bit of a design challence for me… Just how small, how simple, can I make a focuser and yet still provide excellent usability. My latest Helix 1-14 design is my best yet.
A simple helical crayford focuser
As my 3D printer design skills improve I applied lessons learned and the unique capabilities of an FDM printer to the problem of a focuser. After a bit of a journey I have arrived at a design I can consider finished. Is it the final design? I may tinker some more, but I am satified for the moment.
The design is based on a few ideas from here and there, products I have seen or used, internet postings from others faced with the same challenge. I am not one for just printing someone else’s design, I rarely do that, I want to do my own, and maybe make it better.
For the last couple years I have been exploring 3D printed telescope designs. The latest result of this oddessy is Kinipōpō, a 4.5″ f/4 Newtonian using a entirely 3D printed ball mount design.
Kinipōpō ball telescope 3D model
The Hawaiian word kinipōpō translates as ball or sphere.
A ball telescope offers a number of advantages, the first of which is ease of use. It is simplicity itself to aim at a target, no odd controls, no weird angles, just freely push the ‘scope to the target. As the tube can be freely spun the eyepiece can always be positioned for easy viewing.
The design is an RFT, or Rich Field Telescope. This type of ‘scope is designed to be a low power, wide field ‘scope ideal for enjoying sweeping the sky and providing views rich with innumerable stars. It is not a good ‘scope for planets, the magnification is far too low. It’s prey is large, bright targets, star clusters, bright nebulae, or even the dark nebulae silhouetted against the rich starfields of the Milky Way.
Another ideal target is bright comets. My prototype providing pleasing views of comet C/2022 E3 ZTF a month before preihelion and maximum brightness.
The short focal length does create coma issues around the edge of the field, stars near the edges of the field smear a bit and will not focus. The problem does not seem too objectionable, but it is there.
The design is inspired in part by the classic Edmunds Optics Astroscan telescope, in being both small, portable, and simplicity to use. On the other hand the design offers a number of improvments over the Astroscan. Primarily the ‘scope offers an increased aperture of 114mm compared to the Astroscan’s 105mm, while being very close to the same overall size.
The scope costs about $200 to assemble, the largest chunk of that being the primary mirror. While the needed plastic filament for the 3D printer is cheap, it does take quite a bit of time to print. The largest part, the spherical shell requires over 60 hours on the printer, with many of the other parts being overnight prints. Assembly is not difficult, mostly cleaning up the plastic prints, heat setting a number of brass threaded inserts, and a bit of epoxy here and there.
Three of these little telescopes have been built, and three have been given away. I get photos of them every now and then, fun little telescopes under a dark sky.
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
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.
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.
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 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.
The classic Cave Astrola telescope has become my roll-out, quick observing session ‘scope, often found in my driveway. I have also used it a few times at darker sites when I expect the weather to be damp or dewy as a Newtonian is more protected.
The restored 8″ f/6 Cave Astrola under a dark sky at Kaʻohe
While the restoration job was finished some time ago, I never got around to re-coating the optics. Meanwhile the telescope has seen good service on many occasions as I enjoyed this fun-to-use instrument.
The optics did need some attention… The primary mirror from the Astrola appeared to have not been re-coated since it was made in 1978. Thus the aluminum coating was over 40 years old. While the coating looked bad, it was still serviceable, producing reasonable images.
Still, the loss of light due to the old aluminum coating was probably reducing the effectiveness of this 8″ telescope to something more like a 6″ telescope. I had meant to get it re-coated some time ago, but we know how these things work.
When shopping for a focuser you face a lot of choices. From the cheap eBay Chinese options to the top-of-the-line Moonlights and Feather Touch. I once again perused these options when buying a new focuser for the Cave Astrola.
The ScopeStuff 2″ Crayford Focuser mounted to the 8″ Cave AstrolaIt has been a while since I looked at what was out there. So I spent some time shopping and wandering website re-educating myself on what the options were.
I considered the cheapest end of the market, a few options found on eBay, and again at the top-of-the-line, machined works of art that cost as much as some telescopes. This time I was limiting the budget for restoring the Astrola, not wanting to spend much more than a hundred on the focuser to keep the cost of the whole effort down.
I do enjoy a nice project I can work on, get my hands dirty, and use my skills. A classic telescope in need of restoration? Just the thing.
A restored Cave Astrola 8″ f/6 Lightweight Deluxe
This telescope was literally rescued from the trash. Matt, the owner of the excellent Mountain Road Cycles in Waimea found the telescope at the transfer station.
Matt put a message into the folks at the observatory, who represent more than a few of his customers. The info was quickly forwarded to me, as everyone here knows I build and restore telescopes for fun.
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, from Phil HarringtonWhen 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.
