Jump to content

  •  

* * * * *

A 160 mm (6.3“) f/6.5 binocular telescope


Discuss this article in our forums

A 160 mm (6.3“) f/6.5 binocular telescope

Thomas Möller

 

A 160 mm (6.3“) binocular telescope

 

1.  Introduction

 

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 [3]

 

Fig.1 Cover page of the Carl Zeiss
Catalogue “ASTRO 24”(~1915)
Astronomical binoculars and double refractors combine very aesthetical views and ease of use. Just a reminder, this is a rather old technology (figure 1). With increasing aperture, however, the whole setup, in most cases based on commercially available telescopes is getting heavy and the instrument departs from the idea of a 'grab and go' telescope in the spirit of the best telescope is the telescope you use often. Large instruments based on reflectors can certainly give breathtaking views, but usually transport and mounting is cumbersome.

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 [2] 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.

 

 

I.  Construction

 

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
the end.
While most binocular telescopes are built from two commercially available refractors, the present design is based on two lenses while the remaining part is constructed with the aim of a stiff, compact and lightweight binoscope solely for visual observation. The two 160 mm apochromatic lenses are made by Pal Gyulai who is now making the lenses for the CFF telescopes [4] in Hungary and patented Erecting Mirror Systems (EMS) from Japan. The present telescope is not a typical ATM project, key parts of the telescope, optics, mount and the construction are made by Great Star [5], a small company in Germany. The lenses are apochromatic oil spaced triplets, with one aspherized surface (Ohara FPL 53 and Schott N-ZK7 glass) in a custom made slim mount promising nearly perfect correction (Strehl better than 0.95 for green light). The fast f-number (f/6.5) results in 1050 mm focal length and allows constructing a rather compact telescope with large field of view (2.5 degree). Guiding the light to the eyes is accomplished with the EMS mirror systems (custom EMS-UXL-Premium [1], figure 4) consisting of two mirrors reflecting under 60 degree angle giving an upright, true side image. With protected silver coatings a transmission of 97 % is achieved. The interpupil separation can be adjusted with helical focusers, collimation can be fine-tuned by x-y knobs and focusing is achieved with 2“crayfords. The telescope tubes are made from carbon blackened on the inside with a special paint and reinforced by carbon rings which also serve as stray light baffles. They are connected by compact and stiff aluminum bridges in the middle and at the back of telescope. The dew shields are lightweight sandwich constructions with velour on the inside and carbon on the outside. Thanks to all these efforts the total weight of the telescope could be kept below 12 kg (23 lbs.).

 

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.

 

II.  Mount

 

Fig. 5 CAD drawing of the single arm fork mount. The
binoscope can be fixed on the rotating upper part
with two screws.
The symmetric construction allows binocular telescopes to be mounted with single arm forks thus saving additional weight without losing stability. Figure 5 shows the construction of the fork mount. The different components are made on a CNC milling machine from aluminum. The size of the first mirror (115 mm long axis) in the EMS systems sets a limit for the separation of the two optical tubes. In the present case of a 160 mm f/6.5 instrument the upper part of the fork mount needs to be rather thin, it is only 25 mm wide, otherwise vignetting would result.  Lightweight bearing elements of type LEL from Franke (Germany) with 4 race rings (figure 6) allow a stable movement of the telescope. These bearing elements can be directly incorporated into a construction and accept radial as well as axial forces. In order to save further weight a hollow construction is used for the mount. The total weight of the mount is 2.3 kg.

 

 

III. Tripod

Fig. 6 Bearing element LEL from Franke [5], 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.

 

IV. Accessories

 

Fig. 8 Construction of tripod head, three 32x32 mm,
2 mm thick carbon profiles provide the basis.
Some accessories such as a finder or an observation chair make the observation more comfortable. Since the whole construction is designed with “grab and go” in mind the observation chair is also constructed from carbon profiles and rather light. The height of the seat can be continuously varied between 20 and 90 cm (8- 36 inch). Since the EMS mirrors allow comfortable 90 degree view a finder with the same view angle is desirable. This is accomplished by placing two mirrors similarly to a pentaprism in front of a red dot finder. The binocular telescope accepts 1.25“ and 2“ eyepieces. With 46 mm diameter field of view, a comfortable 25 mm of which are not subject to vignetting, a maximum field of view of 2.5 degrees can be obtained. Presently, my favorite eyepieces are a 30 mm widefield from APM (46 mm field stop, 85 degree AFOV), 17mm and 10 mm TV Ethos, and 6,5mm Baader Morpheus, giving 36x- 160x magnification. Higher magnification can be achieved with the aid of a TMP Barlow lens in a special housing with a 2“ thread.

 

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 [6]).

 

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.

 

References:

 

(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 14 others like this


23 Comments

Great article and super build.

The light gathering power of two 160mm aperture telescopes is similar to a 9" diameter reflector.  Can you comment on the difference in view between a true binocular like yours and simply using a binoviewer in place of an eyepiece on a 9" reflector?

Great article and super build.

The light gathering power of two 160mm aperture telescopes is similar to a 9" diameter reflector.  Can you comment on the difference in view between a true binocular like yours and simply using a binoviewer in place of an eyepiece on a 9" reflector?

The key difference is the field of view, typically the maximum field of view with a binoviewer is much smaller than that of a true binocular. It depends on the designe, often you need a glass path corrector which increases the focal length. Then, even if you can get 6 mm exit pupil the image is darker because the light is distributed to two eyes.  With a true binocular telescope you can also use 2" eyepieces, with the 160 mm instrument you get 2,5 degree ( 80 degree aparent) field of view with 35x magnification, with 5.5 mm exit pupil.  17 mm Ethos give 65x magnification, these are my favorite eyepieces for binoviewing. One the other hand, I should add, I have never looked through a 10" reflector with binoviewer.

 

Thomas

    • sftonkin, Mark9473, KeithC and 4 others like this

Incredible, an absolute dream instrument!

A well balanced compromise!

Congratulations!

Your binocular makes my APM 100 ED APO a toy... a superb binocular Thomas!

In my bino M13 is still a nebula...

 

As always: you get what you paid for.

 

Garret vd Veen

Spectacular Instrument! Beautifully made. :)

Thanks a lot for all the praise, it took a while to complete the instrument!

 

Thomas

Great binoculars. I wish I could have a setup like that.

    • faackanders2 likes this
Photo
Perseus_m45
Jul 12 2016 02:44 PM

Awesome build . That setup would be great for comet finding !! 

Magnificent! Great article. Thank you for all the generous photo's as well. I can't even imagine the view through these,

    • rookie likes this
Photo
faackanders2
Jul 13 2016 08:07 PM

awsome light weight 160mm binos.  Knowing what you know now, if you had to do it all again what would be the estimate cost of the binos and tripod/mount?

awsome light weight 160mm binos.  Knowing what you know now, if you had to do it all again what would be the estimate cost of the binos and tripod/mount?

I can give only a very rough estimate. Actually, I think I would have difficulties to do it again because I don't know whether I could get the 160 mm apo lenses again.

Just as a rough estimate, the prize of the binocular telescope alone is similar to the Binoptic II 130 mm LZOS, the mount 2-3  times the binoptic fork mount, the tripod a little bit less than the Berlebach Sky. If I could have done everything myself ( workshop with CNC machines etc. is needed)  then I could have saved 30%-40%  or so. Just another comparison, AOK in Switzerland offers a Takahashi 120 mm binocular telescop with forkmount. If you add tax you will end up with a similar price. 

    • jdown likes this

Very nice!! Turns out I have two 152mm F6.5 achromats. Been thinking about making a bino.

Very nice!! Turns out I have two 152mm F6.5 achromats. Been thinking about making a bino.

This will be a very nice bino, especially for the Milky way.

Well, the price may be similar to the Binoptic II, but your objectives are 30mm larger, and your binos are almost 10lbs lighter! I would never have imagined that it would be possible to put together a fine optical binocular of this size at that weight. But it's also obvious that you have skills way beyond what most of us could muster. The final result has to be surely worth the effort (which appears considerable). We are all appropriately envious.... :)  :)  :)

Photo
piero pignatta
Aug 12 2016 03:30 PM

admired and delighted! the warmest congratulations!

a "miyauchian" record

bravo!

Phenomenon build project. Well done. 

Photo
CounterWeight
Aug 27 2016 11:30 PM

What an amazing visual instrument you have created.  Congratulations.  The build and thought going into this, and the results, I agree are admirable.  Another well done!

Photo
denis0007dl
Sep 09 2016 04:49 AM

Here I describe a 160mm 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.

Click here to view the article

Excellent review!

Thans for sharing that!

Photo
rogeriomagellan
Dec 31 2016 04:37 PM

Very nice!! Turns out I have two 152mm F6.5 achromats. Been thinking about making a bino.

Hi. Are your f/6.5 refractors from ES?

Photo
rogeriomagellan
Dec 31 2016 04:38 PM

The view through this binocular telescope must be awesome. 

Fantastic report.  

 

I am in the slow and long process of building an 80mm f/6 triplet based binocular (and even this is pushing my pocketbook to scream levels) but this kind of article makes me want to accelerate my pace.  

 

A beautiful piece of gear!   Thanks for sharing! 

Photo
HonoluluWalt
Feb 18 2018 05:31 PM

I think that I should sell one of my my cars, or mortgage my home, and buy one of these.  After all, which would I rather have in a backyard:  one of these, or some tiny swimming pool of less than 20 yards in length (within which it is impossible to get a decent workout anyway)?



Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics