Category: Astronomy

Exploring the cosmos

Kinipōpō – A Small Ball ‘Scope

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
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.

Kinipōpō ball telescope 3D model
Kinipōpō ball telescope 3D model
Kinipōpō ball telescope 3D model
Kinipōpō ball telescope 3D model
Kinipōpō ball telescope 3D model
Kinipōpō ball telescope 3D model
Kinipōpō ball telescope 3D model
Kinipōpō ball telescope 3D model
A simple helical crayford telescope focuser
A simple helical crayford focuser
Mirror test stand with 6" telescope mirror
Kinipōpō under the Stars
Truss tube clamp on the Kinipōpō ball telescope
Three copies of the Kinipōpō ball telescope

Testing a Mirror

As I have observed lately, most of the small telescope mirrors available right now are out of China, most of those produced by one company, Guan Sheng Optical or GSO. If you want a small mirror, say a 6″ or 8″ mirror, there is not a lot of choice, the mirror makers in the US generally do not do anything smaller than 10″.

Foucault knife edge test
A textbook Foucault knife edge test image on a 6″ f/4 mirror

The GSO mirrors range from decent to pretty bad, with no way of knowing what you will get when you order, just luck of the draw.

But how do you tell?

Continue reading “Testing a Mirror”

Confusion of Time

My body is awake.

World Time Zone Map
A map of world time zones from Wikimedia

At this point I know not to trust my sense of time or internal clock, I have traveled across far too many time zones. Entebbe to Portland required 27 hours of travel and crossed ten time zones. My body is simply not to be trusted.

The previous evening had consisted of little more than making it from the airport to my parent’s house, then directly to a long sought bed.

The clock reads nearly 7am.

How can this be? The time seems wrong and I have no confidence in the old LED alarm clock in the guest bedroom. Was it set properly? I fumble for the cell phone to double check the time. The phone confirms the seemingly inaccurate time.

Continue reading “Confusion of Time”

Neptune at Opposition

Today the planet Neptune will pass through opposition, directly opposite the Sun in our sky. The planet will be well placed for observation all night long, rising at sunset, transiting at midnight, and setting at sunrise. If you are looking to observe Neptune, it is currently shining at magnitude 7.8 in
in southern Pisces just south of the circlet.

Neptune from Voyager 2
Neptune from Voyager 2, Credit: NASA /JPL

As the outer planets Uranus and Neptune move so slowly across the sky, the timing of oppositions is driven by the Earth’s orbit and occur each year at nearly the same time. Neptune’s orbital period is 164.8 years, taking over a century and a half to circle the celestial globe once. As Neptune was discovered in 1846, it has completed a little over one orbit since discovery.