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A 160 mm (6.3“) f/6.5 binocular telescope
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A 160 mm (6.3“) f/6.5 binocular telescope
A 160 mm (6.3“) binocular telescope
Binoculars, while often regarded as 'entry level' observational tools, offer aesthetically very pleasing views. Now with larger-sized binocular telescopes ('binoscopes') becoming available they are more often used as serious observing instruments. Basically, the instruments can be divided into three classes:
- binoculars with straight view and typically fixed eyepieces and magnification
- astronomical binoculars and double refractors with comfortable 45 or 90 degree view and often interchangeable eyepieces [1,2]
- large instruments based on reflectors - usually Newton telescopes 
|Fig.1 Cover page of the Carl Zeiss|
Catalogue “ASTRO 24”(~1915)
Here I describe a 160 mm apochromatic binocular telescope complemented by a mount and tripod aiming at a well-balanced compromise between optical performance, size and weight. I started the project already several years ago, the first version is described here at Cloudy Nights. Meanwhile a new, lighter and stiffer mount and tripod are finished and I think it is the right moment for describing the whole instrument.
|Fig. 2 160 mm f/6.5 apochromatic lens made|
by Pal Gyulai, in a slim mount for binocular use
(3,5 kg mass.)
Some background, my addiction to binocular observation started almost 10 years ago with the purchase of a commercial 115 mm double refractor from Bionoptic  with apochromatic 115 mm f/7 TMB lenses. While I was very pleased by the views, I sometimes missed aperture, especially for galaxies aperture helps seeing details such as spiral structure which is otherwise hardly visible. This was the starting point for building a larger binoscope with the important boundary condition that the weight should not exceed the 12 kg (~26 lbs.) of the TMB binocular. This allows easy transportation either to a balcony, garden or a dark site.
|Fig. 3 CAD drawing of telescope tubes and|
mount. The tubes are connected in the front
part by CNC milled pieces and a bridge at
|Fig. 4 Top View of the binocular telescope with EMS Mirror systems, total weight 11.8 kg (without eyepieces). The|
handle and two screws above the center of gravity allow easy transportation and fixing the binoscope on the mount.
|Fig. 5 CAD drawing of the single arm fork mount. The|
binoscope can be fixed on the rotating upper part
with two screws.
|Fig. 6 Bearing element LEL from Franke , allowing a|
lightweight (0.07 kg for 70 mm diameter) and stiff construction.
The fork mount is fixed on top of a tripod with a central column. The tripod head is made of carbon and aluminum profiles, details of the construction are presented in figure 8. An 85 mm outer diameter carbon tube serves as the central column. The legs are made of 85 mm wide, 1.2 mm thick carbon profiles. Although the tripod weights only 2.2 kg its stiffness exceeds that of many popular commercially available, wooden constructions with almost 4 times higher weight. This comes at the price of a fixed tripod height, but in combination with a binocular telescope this is not a real disadvantage.
|Fig. 7 Single arm fork mount, in the workshop, side view.|
|Fig. 8 Construction of tripod head, three 32x32 mm,|
2 mm thick carbon profiles provide the basis.
V. Under the sky
|Fig. 9 Tripod constructed from carbon profiles.|
Thanks to the lightweight construction (in total 16.2 kg/ 35 lbs. for telescope, mount and tripod) the set up can be easily transported to a dark sky, either by car but the latter case I take the lenses and the EMS into the hand luggage. A few minutes after arrival, typically less than 5 minutes, observation can start, oil spaced triplets cool down rather rapidly. The instrument is a general purpose telescope, it gives very nice views of the moon, especially the crescent at low magnification, but also of planets. For instance Jupiter with the great red spot or the Cassini division in the Saturn rings. The Milky Way, in particular open and globular star clusters, galactic and dark nebulae are favorite objects of large binoculars. Especially in combination with ultra-wide angle eyepieces just sweeping the Milky Way is a lot of fun. The light gathering power of two 160 mm lenses is also sufficient for deep sky observation of galaxies and galaxy clusters. Binoculars show certainly more than a telescope of the same size, but the key aspect is the pleasing view. M31 with its two companions just fits into the 2.5 degree low power field of view and two dust lanes are visible in M31. Under a perfect dark sky, M51 shows spiral structure with direct vision and irregular (e.g. M82) or interacting galaxies, such as NGC 4435 and NGC 4438 in the Virgo Cluster show structure. But, don't expect too much from a 160 mm instrument, weak galaxy groups such as Stephens Quintet can be seen but, a large Newton telescope shows much more details. On the other hand, globular clusters like M13 give some very nice unique '3D view' although the image in a large reflector telescope is certainly brighter.
|Fig. 10 115 Binoptic 115 mm and 160 mm binoscope on top of the|
transportation bag for the 160 mm instrument.
|Fig. 11 Observation chair, seat height can be continuously varied between 20cm and 95cm, total weight 0,95 kg (for details see ).|
VI. Final thoughts
|Fig 12 Complete set up: Binocular telescope, mount, tripod and eyepiece bag.|
Binocular observation allows very pleasing, aesthetic views, but is quite costly. This is especially true for a 160 mm apo bino which is certainly a luxury telescope. For the same price one can get a very large reflector telescope. I believe, serious binocular observations become only possible with a comfortable 90 degree view. Considering the costs of high quality mirror systems or equivalent prims plus a set of eyepieces, I estimate that a minimum aperture of at least 70 to 80 mm is needed to justify their price. There is no distinct upper limit, but size, weight, price and availability of lenses make double refractors with apertures above 200 mm extremely uncommon. The smaller instruments with 70- 100 mm are excellent instruments with wide fields for all kinds of planetary and galactic objects. Even larger binoscopes with 150 mm aperture open the door to serious observation of galaxies. Since the combination of a smaller binocular telescope with a large reflector is very universal and efficient, larger, e.g. 150 mm binoscopes will certainly be a niche product. Such telescopes can offer some of the most beautiful views of the sky, but at a high price and not for all objects. It will be interesting to see if other, further improved binoscopes will follow or whether even high quality commercial products will enter this niche. In any case, such instruments need to be a thoughtful combination of telescope, mount and tripod, otherwise weight and ease of portability will suffer. Finally, I’d like to thank Pal Gyulai, Tatsuro Matsumoto and Steffen Noack (Great Star) for all their help, discussions, enthusiasm and support which provided the basis for building this telescope.
(1) Erecting Mirror Systems (EMS), http://ems-bino.com
(2) Binoptic, noble double refractors, http://www.binoptic.de/web_us/index.html
(3) e.g. large amateur binoculars, http://www.brucesayre.net
(4) CFF telescopes, http://www.cfftelescopes.eu
(5) Great Star, http://www.greatstar.de/index.html
(6) Astrotreff, http://www.astrotreff.de/topic.asp?TOPIC_ID=183128, this page presents various designs of lightweight observation chairs (in German)
- Chopin, mattyfatz, Gordon Rayner and 15 others like this