Designing the Perfect Travel Telescope

I love getting away with my family in a remote location. Usually, we get a lot of opportunities to place the tent in a very dark sky location. No late meetings, no obligations early in the morning, good weather.... the situation is just ideal for stargazing but, there is no way I can squeeze a Dobsonian in the trunk of my car.

I have been working for quite a reasonable time on the design of a modern travel telescope. I got the inspiration from Pierre Strock, who designed a travel telescope based on a 250mm truss Dobsonian around 2007. While the design is quite compact, there is still room for improvement. Another source of inspiration is Roel Weijenberg, who also got inspired by the Pierre Strock model. Roel managed to reduce the weight and size to a new level.

Figure 1: a model developed by Roel Weijenberg, who also

got inspired by the Pierre Strock model.

I have been planning to commercialize my design from the very beginning, but without sacrificing some key features I was looking for me and my kids. The main idea is to develop a reasonable big aperture telescope easy to carry but also easy to collimate, set up, and use, including kids. When you include kids as target users, you need to take extra care of the robustness of the product.

I also wanted to develop a telescope that can be eco-friendly and last for a very long time. For that reason, I choose bamboo and aluminium as the predominant components. The 3D printed components used are also environmentally friendly.

Another key requirement was to be able to reuse existing optics of traditional Newtonian telescopes and retrofit some of the existing components (spider, secondary holders, cooling fan and mirror cell). I used GSO 8" f/4 for my first model because kids are expected to be the primary users. Grown-ups can sit on the floor or use a camping chair to observe through the eyepiece. Having said that, the model works just fine with the standard 8" f/6 Dobsonian optics.

The traditional Crayford focusers are quite confusing for newbies, especially for kids. In addition to that, they are usually quite heavy. In order to keep the telescope in balance, the weight on the top of the telescope should be reduced as much as possible. The bearings have enough friction to resist a moderate amount of imbalance; however, this friction can also make it difficult to position the telescope accurately. For that reason, I decided to use a 1.25" helical Crayford focuser, also designed by myself and good but lightweight eyepieces.

The eyepieces I use with the 8" f/4 (800mm focal length) and 8" f/6 (1200mm focal length) are:

• Celestron Omni 32mm (x25 magnification, 1.76° real FOV)

• Intes Micro Q75 WA 20mm (x40 magnification,1.75° real FOV)

• Intes Micro Q75 WA 12mm (x66.7 magnification,1.04° real FOV)

I decided to incorporate a red dot finder because it is very lightweight but I also want the telescope to be extremely easy to find objects. The initial idea was to use the Skylabs NZ Smartphone Finder Mount for Skeye PUSHTO. Unfortunately, the weight of a standard smartphone can unbalance the telescope. For that reason, I have also been working on a magnetic encoder system managed by a low-power consumption Raspberry Pi Zero W. Thanks to the WiFi capability of this Raspberry model, I can take advantage of the telescope setup available in SkySafari Pro (Alt-Az. Push-To). The tiny computer, the encoders and the USB battery are located on the Dobsonian's base, which also helps to keep the telescope's balance under control.

I also included a light shroud, not only to avoid stray light entering the telescope but also to prevent kids from touching the mirrors with their hands.

I'm still working on this model and I'm open to suggestions. If you have an amazing idea or a requirement that has not been considered in this post, reach me out! You can influence the final design.