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DocTelescope 20" dobson "Herschel": my review

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#1 annoluce

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Posted 14 June 2020 - 11:09 AM

Disclaimer: This review is due to my initiative only. I have no business relationship with DocTelescope and do not perceive any gain or benefit of any kind to write this review; I am simply a passionate and satisfied owner and customer.

 

DocTelescope 20" "Herschel"
 

INTRODUCTION
I have been observing the sky since I was 13 years old, when my father gave me as a present a little "114 mm", the classic 4" Newtonian which many children start observing the sky with.
After those discoveries, I continued to observe the sky and I became a passionate observer of deep sky objects; when I went to University, I bought a Celestron Ultima 2000 that I still own today, and after thirty years, it continues to give me beautiful visions of the starry sky and the jewels that this celestial treasure chest offers.
After a year with a SkyWatcher 12" Flextube, which gave me enormous satisfactions, I was looking for a step up to a superior instrument; a telescope that I could call "definitive" (even if this word for us stargazers who love diameter doesn't have much meaning...).
I decided to grow up: I wanted to become a "half meter" man. Find the Cloudy Nights thread HERE.
I put on sale the 12" and started doing a wild scouting of Dobson telescope manufacturers and suppliers. I considered many brands, both artisan and more "commercial" off the shelf.
I live in Italy, so there is not a lot of choice when calling dobson manufacturers in our lands; you have to contact laboratories abroad, and there is not a lot of choice neither. In Europe we can rely on dealers and distributors but they do not abound. I considered the Italian Reginato, who produces wonderful dobsons, but largely off budget for me, and very heavy. I was looking for a transportable "half meter" instead.
Last but not least, the budget. Nobody wants to be kicked out of the house by their wife, do they?
(I had already many times used the old trick of saying "dear, I had a love affair and cheated on you with a colleague.... No, no it is a joke come on, I bought a new dobson!").

 

SCOUTING
One thing my 12" SkyWatcher taught me: the back is important, observing the sky is as important as loading and unloading the car, assembly and transport. I don't live in Arizona unfortunately so I can't count on dark skies from the backyard: I have to haul the dobson for at least 100 km in search of clear and transparent skies, so do many.
So I was looking for a transportable telescope, lightweight, mountable and removable quickly, rigid when assembled, with tracking and go-to, and that would fit into my little Dacia Sandero Stepway: a desperate feat for these diameters!

 

I had my eye on:

 

- SkyWatcher Stargate 20"

- ES Ultra Light 20"
- Orion Skyquest go-to 16"
- Meade Light Bridge 16"
- Taurus T500 20"
- Sumerian Alkaid 16"
- Obsession 18" UC
- Hubble Optics 20"

 

I discarded these telescope brands for several factors: some did not offer the 20" I wanted; some did not offer go-to, others were not as transportable as I wanted, or overly priced.
The only ones that really met all the requirements were: the Obsession 18" (I didn't want to choose the 22" for budget reasons) and the Hubble Optics 20" F3.7. I was very close to buying the latter.
Then a friend of mine recommended DocTelescope to me. It's an Italian company that produces Dobsons. A family business... Its founder is Marco Guidi, a nice enthusiast who lives in Rovigo, in the beautiful region of Veneto.
A friend here in Rome had a 20" built by DocTelescope, so I could try his scope on the field.

 

DESIGN AND BUILD
So was born this adventure I'm telling. I contacted Marco who immediately showed a very kind attitude.
On the phone we talked a lot and defined all the project "requirements".
Marco is someone who supports and doesn't leave you alone. If there is a change to make, even during the work, you ask him and he does it.
Marco proposed me a 20" F3.7, with a GSO primary and a Zen secondary. Zen is an artisan laboratory of precision optics that operates in Italy, one of the most famous. This way I would have had a very comfortable eyepiece height at the Zenith with an aperture ratio still acceptable for the aberrations inherent in the optical scheme.
We had a lively discussion about plans and projects on email and whatsapp. I told him the binoviewer was essential to me, and he "pulled" the focus out for 12 cm, mounting a 120mm TS Optics secondary (I chose TS Optics instead of Zen).
I asked him to move the finder's position, all right. I asked him to flip the observation side (eyepiece side), all done. Then I wanted the Nexus DSC instead of Argo Navis, so I could connect it to the smartphone with Sky Safari. All modifications have been done perfectly.
Working with Marco is like designing your own Dobson personally: every request can be discussed, designed, thought and then realized. Marco is a passionate but also a big expert and he knows how to advise what is right and what makes less sense to do. The design of his dobsons is made with PC programs, laser cutting machines, handmade craft and metal and woodworking components.
Although DocTelescope offers the possibility to mount any optics, mainly Marco suggests Zen and Giacometti optics, which are the best optical manufacturers in Italy. But customers can mount any optics of their choice. I have chosen, for budget reasons, a GSO primary mirror. The GSOs are now machined with numerical control and they are quite good nowadays, I knew anyway that I was dealing with a compromise. Marco doesn't build optics, so it was my call. I opened recently a thread on CN about this primary to know if it can be re-shaped, because sometimes gave me concerns, probably due to the collimation and seeing of the evening. I think the issue experienced during one or two nights are mainly due to the seeing.
I now reserve the right to do further tests, to understand if the problem is the seeing, the collimation or the secondary not perfectly flat. The primary GSO shows a perfect Ronchi diagram, so most likely the problem is elsewhere. I've had excellent evenings and bad evenings, so seeing is also important when you have a 20".

 

Details of the roker and primary cage
Primary floating cage
Secondary cage

 

 

THE TELESCOPE
The telescope can be completely disassembled into the following basic parts:
- Secondary cage
- Truss tubes
- Lower cage of the truss structure (can be dismantled or left in place)
- Headmaster's cage with “gondolas”
- Base rocker box
- Primary mirror
- Nexus DSC go-to and stand
- Altitude Encoder

 

Truss frame

 

SECONDARY CAGE
The cage of the secondary consists of two laser-cut metal circles and sports a gorgeous electric Moonlite focuser. The two circles of the cage are joined with golden metal bars, another aesthetic touch for the telescope. The secondary is held in place by four spider spokes with thin section, fully adjustable to setup the position and offset of the secondary, which however had been factory adjusted by Marco to perfection. I didn't have to touch them anymore. The structure is very light (it can be hold with one hand!) and very stiff. A single person can easily setup the truss tubes in place.
The structure is perforated to increase lightness while maintaining rigidity. One thing I didn't like about the Hubble Optics is the position of the secondary, outside the cage, which exposes the secondary to moisture and requires the use of a very long dew shield. The secondary in the DocTelescope, on the other hand, is placed downwards and remains inside and protected.
The secondary, as well as the cage of the primary, has ball connections for quick coupling. Simply insert the truss ball and turn a lever and the structure becomes very rigid. The secondary's cage is also very thin, so it transports well and can be handled with one hand. Marco provided me with a beautiful wooden box to hold the secondary, where I can also put the light shield cover and the rubber dew shield. On the cage of the secondary there is a handy attachment base for the finder. I would have liked to have two attachments, so I could also put a red dot, but I solved it by adding a second base on the side of the finder support. The structure of the secondary also serves easily as a base to support the rubber dew shield (which I made out of a decathlon Yoga mats), which I keep in place using camping straps.

 

Secondary cage details with attachment for finder
 

SECONDARY
The secondary is TS Optics, a German company that makes good optics. Marco has glued it perfectly to the structure of the cage, leaving also the necessary space for air passage and acclimatization. At my request, Marco also added springs to make collimation easier. I reserve the right to check the flatness of the secondary with a specific test.

 

Secondary collimation screws
Secondary cage
Secondary cage and wooden box
 

TRUSS TUBES
Truss tubes are a masterpiece: light and very resistant. They have a "carbon" look that I really like. They are only 145 cm long and can be easily carried in a fishing rod bag that I bought for a few euros in a shop. The telescope has 8 truss tubes, numbered so that they can be placed in the same position and thus maintain the consistency of the collimation. The trusses have balls at the ends so that they can be attached quickly. They are very light and can be lifted "with one finger". The structure of the trusses is formed with 2 truss tubes on each side of the square, which gives the telescope a remarkable and surprising rigidity once mounted. I personally find that these trusses give the telescope a very attractive look. You can see them in several photos.

 

Detachable truss frame

 

PRIMARY CAGE
The primary's cage forms a single element with the dobson gondolas, which run on the rocker box. The structure is made of black painted aluminium, very light and beautiful to look at. Eventually I can put the primary cage in the car without destroying my back!
The two gondolas are made of birch wood, painted gold, really a touch of art to the telescope.
The structure to which the truss tubes are attached is a metal “square” frame that is connected to the primary cell with 4 knobs. In this way, very clever indeed, the entire upper structure of the telescope (secondary, truss) can be removed as a single piece, lifted and placed in the storage area. In this way the telescope can be mounted in few minutes (5 or less). Of course this only applies when observing from a fixed location, in a backyard or observatory. I leave this metal "square" always attached to the primary cage and disassemble the trusses instead.
The primary is resting on an 18-point floating cell that holds the mirror in position only thanks to gravity. There are two steel metal pins on the front area that prevent the mirror from moving and falling, but the weight of the mirror is held by the cell. These two pins are adjustable (this serves to keep the mirror on the center of mass line) through a rear knob. Other two knobs are used instead to control the collimation adjustment screws, which is really convenient and quick.
The floating cell can be detached to avoid damage during transport.
At the center of the primary cell there is a nice 20 cm fan that Marco has installed to optimize the acclimatization time of the primary. There is a circuit cable that connects the fan to an electrical jack on the external structure, which can be easily connected to an external battery box or to the main power supply.
The structure that supports the floating cell is made of a metal triangle bars, so it is very rigid but light. In the aluminium tubes Marco has made threaded holes for the screws, already prepared to screw in counterweights.
The gondolas slide on Teflon for a precise but at the same time soft movement in altitude. I prefer to have a certain “density” with the altitude movement, it also helps with the balance. However, the movement in altitude is never rough.
The gondolas are made of wood covered with aluminum metal plate that slides on Teflon. The gondolas are reinforced with gold painted aluminium tubes. There are two aluminium "carbon look" bars that reinforce the gondolas on the upper side.

 

Primary mirror box
Primary cage
Detail of the primary cage structure
Details of the half ball attachment clutch
Prumary fan
 

ENCODERS
The ServoCAT encoders are 40000 PPR, very precise in tracking and pointing. The azimuth encoder is installed in the rocker box, the altitude encoder is installed on the side and must be mounted and removed each time, but just unscrews with an Allen key. In any case its cable always remains connected.

 

NEXUS DSC, ALIGNMENT AND TRACKING
The Nexus is a really high-performance go-to computer database. Very easy to use, it aligns with 2 stars (I always use the Polar and another star according to the convenience of the night). Once aligned with 2 stars the tracking and pointing are very good. With Sky Safari I always know where the telescope is pointing because I can see the "circle" that corresponds to the field framed by the eyepiece in that moment. I can move the telescope by hand by loosening the clutches without losing alignment. You can aim with push-to, go-to or manual. I have to say that the Nexus is great, but I almost always use Sky Safari for both pointing and object finding. The telescope has a control panel that allows you to move in 4 directions with 4 speeds, from "center" to "slew". The hand control is comfortably equipped with a magnet to place it next to the Nexus. With Sky Safari I can still operate the telescope while I am at the eyepiece, using the virtual buttons. Generally I get enough alignment precision to centre an object in the field using 100x to 150x magnification.
Marco also manufactured a nice stand for the Nexus, made of a PVC plate which screws on the side of the scope and can be oriented with a ball head.

 

Sky Safari rules
Detail of the cover
 

BASE ROCKER BOX
The base contains the azimuth encoder, ServoCAT motors and support bearings for azimuth rotation. The rotation is very smooth. Once the clutches are closed, the telescope remains stationary and firm.
The motors are very powerful, they are powered by a 12V motorcycle battery that I placed in the base of the telescope resting with Velcro straps on the metal beams of the base itself.
The slew speed is quite high, there is a minimum delay that does not bother me much. I like the noise of the engines very much and it is a "music" that I have now associated, like Pavlov's dogs, with wonderful visions of the starry sky. The base will weigh around 10kg (I'll be more precise), it is lifted comfortably with the arms and fits into the car without problems.

 

Primary installed

 

ASSEMBLY, DISASSEMBLY AND TRANSPORT
These operations are the processes where the DocTelescope really shines. I stow all the pieces in the garage, having a wooden trolley on which I put the base and the primary cage; then I have a bag for the trusses; a wooden box where there is the secondary; finally a wooden box (very strong) where I keep the primary mirror. Everything is comfortable to keep in the garage, the rocker has a very small footprint of 70x70cm. The secondary box is held vertically along the wall of the garage and takes up 20 cm. The case of the primary is just over 50 cm by 10 cm in height. Each piece has its own trolley with wheels so I drag it to the car with a finger, and then I load it without problems. In a photo you can see all the elements comfortably stowed inside my Dacia Sandero which is a small car.
I pull down the seats, then I fix the secondary box. On top of it I place the rocker box (which I fix with a rope to the seat). Behind I put the gondolas of the primary on one side, with polystyrene material underneath. The trusses are placed between the dashboard and the passenger seat. The primary is placed on the passenger seat, it fits perfectly there and also serves me as a "table" where I can place my mobile phones and other things.
Once reached the location, the telescope is mounted in a few minutes. Let's say that doing everything calmly will take half an hour, fixing everything well and also collimating included. I put the rocker box on the floor. I manufactured a wooden base that can be leveled (for when I'm on rough terrain). Then I set up the primary cage, run the steel wire from the engines (the only small "nuisance").
Finally the primary mirror is set in place. Then is the turn of the trusses that once tightened remain standing on their own, making it easier to mount the secondary cell.
At the end of the evening the disassembly is even faster of course.
I am very happy because I have solved my back pain problems forever!

 

All ready for transport

 

BALANCING
The telescope comes out of factory pretty well balanced. Balancing is done by adding the weight underneath the primary cage structure. Marco has provided me with a 2.5kg weight that screws in there.
I added my own weights that screw directly under the cell with the existing threads.
I usually never have to add more than 5kg behind the telescope to balance any accessory (finder, heavy eyepieces or binoviewer).

COLLIMATION
The collimation of the primary occurs through the use of two screws that press on the floating cell, changing the orientation of the primary.
The collimation of the secondary is done with 3 screws equipped with return springs, very fluid but rigid at the same time.
Once collimated, the telescope maintains the collimation all night long, even after pointing it in distinct areas of the sky very distant from each other and at the zenith.

 

COVER
Marco provided me with a beautiful black elastic fiber cover, made by an artisan tailor, which fits perfectly to the telescope, to the millimeter! It is installed using Velcro. There are convenient hooks to hold the corners and the rest is closed with Velcro. There is also an eyelet to pass the focuser through. The cover proved to be really good and able to completely block light and dew.

 

Ready to rock and roll
All covered and set up for the night
 

ALTITUDE AND AZIMUTH MOVEMENTS
The movements are very fluid and free of roughness. The one in altitude is more "pasty" because it has no bearings, the one in azimuth has bearings and is less pasty. Both do their duty very well.
Actually, I have a former version of the DocTelescope Dobson, the latest models are built with a mix of bearings and Teflon in altitude, moreover in the latest models Marco has also added some guiding wheels that hold the telescope firmly on the altitude sliding tracks.

 

Me and the 20" Herschel
Outdoor 3
Outdoor 2
Outdoor 1
 

MECHANICAL QUALITIES
The mechanical qualities of DocTelescope telescopes are extraordinary. I have been able to thoroughly test two samples of them, both are rock solid when mounted. It's really amazing how rigid and resistant the structure can be once mounted, even though it's so light. Try it to believe it.
Every vibration dampens in one second (if ever you get vibrations at all). I'm amazed. The telescope gives a great feeling of solidity and precision when you move it. There is no flexing of the primary mirror during slew. The collimation remains perfect all night long and I don't have to do it again.

 

VIDEO OF THE SCOPE IN OPERATION

 

Video in operation

 

Well, at this point you may be wondering what the experience of observing with this telescope is.
Although the mirror is "commercial", the telescope gives enormous satisfaction in viewing deep sky objects, when the seeing is favourable and the dew level is low. Also, the collimation is paramount.
I have not had the opportunity to use it on planets or the Moon, which are not my field of interest (I will do it soon). Keep in mind however that Marco makes very high resolution observations and astrophotography with these telescopes, you can see some planetary photos on his site.

 

As for the deep sky, I think there is no better story than a report of a typical, fantastic night spent at the dobson when the seeing is favourable. I can easily see 130 objects per night, or more.

 

You’ll find the report, if you want to read it, at this LINK.

 

Max


  • Bill Jensen, wky46, Achernar and 16 others like this

#2 Achernar

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Posted 14 June 2020 - 11:25 AM

Thanks for sharing your very thorough and well considered review. If I was in the market for a 20-inch Dob, based on your review it would receive very strong consideration. I built my own 15-inch truss-tube patterned after the Obsessions, and it's served well for the past ten years. One thing I can tell you from personal experience with it is that a large Dob is a very good choice for observing the planets Mars, Jupiter and Saturn, and you'll find the brighter satellites of Uranus and Neptune easy to find once you know where to look for them. Details on the planets will appear that in the past were only seen by professional astronomers and confirmed by spacecraft that made close approaches to them. They will also almost make you feel like you could see the flags left behind by the Apollo astronauts on the moon, but it will be so bright you'll have a reversed afterimage in your field of vision for a while. In other words, the moon is dazzling literally through a large Dob. As for deep sky objects, even from a quite poor site, I never run out of things to see with my 15-inch, but a 20-inch leaves a 15-inch in the dust when it comes to galaxies and nebulae. Enjoy your telescope, it's a telescope of a lifetime.

 

Taras


Edited by Achernar, 14 June 2020 - 11:27 AM.


#3 Dougeo

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Posted 14 June 2020 - 12:23 PM

Great review and also a very beautiful instrument Max! I really like the ultra compactness and the sleekness. We’ll be eagerly waiting for some observation reports. I wish you many years of enjoyment!



#4 annoluce

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Posted 15 June 2020 - 03:41 AM

Great review and also a very beautiful instrument Max! I really like the ultra compactness and the sleekness. We’ll be eagerly waiting for some observation reports. I wish you many years of enjoyment!

Hi,

thanks a lot! Appreciated. Here you have a winter observation report using this telescope:

 

https://deepskytrave...rag-gruppo.html

 

cheers

Max



#5 annoluce

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Posted 15 June 2020 - 03:04 PM

Errata corrige:

Gondolas of the primary cage are made of wood but covered by steel plate .



#6 grzesznypl

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Posted 20 June 2020 - 09:45 PM

Whats total weight of the telescope?



#7 annoluce

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Posted 21 June 2020 - 04:42 AM

Whats total weight of the telescope?

I did not weigh exactly. I would estimate around 60/65 kg all stacked up.


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#8 GeneT

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Posted 21 June 2020 - 01:47 PM

Beautiful telescope; outstanding review!



#9 turtle86

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Posted 22 June 2020 - 11:40 AM

Beautiful telescope; outstanding review!

 

I agree! 



#10 alexvh

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Posted 22 August 2020 - 10:02 AM

What mirror support system is in this, sling? Whiffletree? Beautiful looking scope




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