The Big One - a Portable 25" Telescope

With little doubt the largest telescope I'll ever own: a huge 25" (635mm) aperture truss Dobsonian!
I built this monster early 2022, using a high quality mirror set salvaged from an abandoned telescope found in Germany (read the complete story of this incredible barnfind here: www.roelblog.nl/2021/10/bizarr.... This video shows the complete assembly of the telescope, which takes less than 10 minutes.
The telescope recently got its "first light" under a really dark sky. An aperture of 25 inches opens up a whole new dimension (pun intended) to observing. The images through the eyepiece were absolutely stunning. Details in galaxies are suddenly so obvious and bright, it blew me right off my observing ladder! :D
More details about the design and build: www.roelblog.nl/2022/04/comple...

[@rickkearn7100]

You are to be commended for not squandering that barn find, your dedication and ingenuity are inspiring. Godspeed. Cheers.

[@dubbleOHnegative]

I absolutely love all of your builds! Any chance of getting some plans somewhere so I can build one of my own?

[@andresdandler7919]

Spectacular. I have built 2 dobs myself. Roel’s designs are next-level, and his construction quality is superb. A true craftsman! I’m amazed that the scope is balanced without any counterweights.

[@NielssBohr]

You should make a living out of this. Because your scope is really beautiful.

[@naveenravindar]

I learned so much more than I was expecting watching this. That telescope is amazing, super impressive work!

[@peterjones958]

That is a brilliant design and build. I have built 2 Dobsonian's myself the largest having a 300mm primary mirror, this one is way bigger. Wishing you many dark skies.

[@mikemccann8822]

Obviously a beautiful setup. I’d like to see plans on your ladder, I love the step up and seat features . That’s what makes tall dobs practical:)

[@daz4627]

I was more impressed by the wheelbarrow design than by the telescope (though the telescope is absolutely sensational!!).😆

[@arcvidelos8008]

Real smart design of the scope, like how the knobs pass thru the secondary cage and turn counter- clockwise to lock the trusses in place- that's brilliant, yet simple. What an awesome observing field too- I'd pay a good hourly wage to observe from a field like that!

[@Roelarex]

Thanks! The observing location however is not extremely dark (SQM 21.0) and some lights of nearby farms can be annoying at times. But it's the best location within 30 kilometers from my home and the 360 degree free horizon is of course very nice!

[@jamesbracken5021]

Brilliant design! Simple, practical and efficient. You evidently invested much time and planning into constructing your beautiful telescope. Many clear nights, well done!

[@willrothfuss8470]

Beautiful build. You'll have a blast with that.

[@ADF_Cable]

Beautiful and ingenius scope! Love it! Thanks for sharing

[@TGUlricksen]

Love it. Thank you for taking the time to share.

[@olivierdamiron7279]

Spectacular. What a beautiful machine. Well done.

[@bezoar36]

Beautiful scope, looks more like the size of an 18" Dob. Reminds me of the Sumerian Alkaid somewhat. Never understood why the traditional Dob hat design was so large. Clear skies and thanks for sharing.

[@FP-fb6jk]

Geweldig machien, Roel! Heel mooi uitgevoerd, weer.

[@XZasCC]

Amazing work, so simple yet beautifully engineered, I'd love to own one haha

[@zetacrucis681]

It's a work of art. And very slick. Congratulations on the beautiful functional design and high quality construction.

[@FP-fb6jk]

A perfect telescope; nothing wrong with it. Impressive achievement!

[@junglejim7664]

Very clever design! John Dobson would be very proud!

[@anandarochisha]

Nice work !

[@ramosiul]

Impressive work.

[@oiivo]

Amazing project! Thanks for sharing!

[@martinlagrange8821]

All of a sudden I realise that for me, a 10" Serrurier is more of my upper limit - while utterly magnificent, my Alfa is just too small for this one !

[@TomPauls007]

Takes “light gathering ability” to a new level, huh?!

[@johnadams9044]

That is one dangerous little ladder you are using, After your fall and feel the effects of gravity, you will then realize your need a real full size ladder.

[@raulleon9656]

Awesome scope!!

[@photonjones5908]

A lifetime of deep sky bliss that fits in your hatchback....and when the fun is finally over, you can be buried in it. -I love my 25"!

[@bb001a]

Very nice design and construction well thought out great job.

[@maxivanov5845]

Good job!

[@amrchhhh]

My main mirror is just like yours secondary... Astonishing

[@AstraPharma-Arabic]

This video has single handedly cured my anxiety!

[@AtlantaTerry]

Why were you anxious? It is so nice that you are now cured of it.

[@farooqec]

Amazing innovation Really appreciable👌🏼

[@jensdecker8864]

the ladder with the seat is also great!

[@alexj9111]

I bet you can see Neil Armstrong's foot print with that telescope. 😄

[@astrosrscat]

That's marvelous

[@MarioAlvaradoJ]

Amazing piece! Have you used it for astrophotography? Would love to see some pictures taken with it!

[@janammerlaan8606]

Wow wat een supermooi bedacht design. Ik kom graag een keer kijken.

[@Nottsboy24]

Nice telescope 🔭 greetings from the UK ☺

[@sjpp71]

That "shut up and take my money" meme came to my mind... Awesome big scope!

[@remblankenburgh]

De video is bijna net zo mooi gemaakt als de telescoop. Een plezier om naar te kijken :-) Prachtig instrument.

[@dyode1]

The excellent and elegant engineering of your dob is evidence of a mature design process. You've clearly harvested your mistakes brilliantly. I presume you remove the mirror face fan when you've reached equilibrium? Even your wheelbarrow implementation is beautiful. Awesome device.

[@Jeff-wb3hh]

Dear Roelarex, that is one of the most beautifully engineered telescopes I've seen. I absolutely love those side bearings. how did you cut the side bearings out so the are so smooth rotating?

[@csabakallai3830]

Wow, that's a giant!

[@johnrombi3060]

Excellent work! Have you experienced any problems with counter weighting the telescope?

[@Legweak]

I would love to have a look through that ! The biggest scope I have looked through was a 10in dob I owned And I was impressed with it !

[@Dr.Pepper001]

I had the joy of viewing through the "yard scope," a 36-inch Dob at the Winter Star Party in the keys. The Horsehead Nebula looked awesome.

[@Dr.Pepper001]

There's an eclipse tonight and wouldn't you know it, the sky is fully clouded over.

[@kristofaron669]

Your secondary mirror is bigger than the primary mirror on my custom-built Newtonian telescope

[@user-ow1vd5gq8i]

Wow,,,, beautiful,,,

[@user-xf8jz9qy9m]

Beautiful! I wonder if the scope gets deformed by its own weight when tilted at an angle. Can you show images captured?

[@Roelarex]

The telescope is very rigid. The trick with building a truss dobsonian telescope is to make the whole structure as stiff as possible. A lot of triangles, diagonal reinforcements in the corners etc. It is very important the telescope maintains its shape and does not bend or flex at all - this way the mirrors stay perfectlly aligned and and the image sharp. Unfortunately I can't show you any pictures made through the scope: it's built for visual use only. For photography you need a very accurate motorised equatorial mount, which I dont have (yet).

[@harrison00xXx]

AWESOME! I really wanted to buy a dobson with 1500mm+, but instead and because of a tight budget i bought a 2nd hand equatorial mount (EQ3-2 sadly) and a 150/750 F5 newton, just good enough for basic astrophotography and its aperture is big enough for visual observation of faint objects. But i guess i wont go away from EQ mounts anymore, too much advantages for astrophotography which interests me a lot more than visual observation.

[@NachoGalvisRuiz]

Gran trabajo. Seguro muy satisfactorio.

[@AtlantaTerry]

Beautiful craftsmanship! What was your estimated total cost of materials?

[@oalithgow]

Beautiful and amazing telescope! What did you use for Azimuth movement? Is it a lazy susan bearing? It looks really smooth

[@Roelarex]

I used a ring of "Ebony Star" Formica sliding over three Teflon disk. It's the most common bearing system for Dobsonian telescopes. To my own surprise it still works great with a scope this size. I thought I would have to add ball bearings afterwards, but decided to keep it this way.

[@quake3quake3]

Where are the lunar images sir?

[@apollohill6733]

Nice

[@lukas3687]

What can you see with the bigger dobson telescopes? Because galaxies you can't hold this targets up to date, after plan.

[@hondaxl250k0]

How can I mirror a satellite dish? The curve is done. And so is the focal point..

[@user-sb5ww7oi6z]

How do the bearings stay so evenly on the track? I see on your other telescopes there is a little piece on the outside of the bearing that prevents it from leaving the track. I don't see that on this however. I'm building a telescope based on studying your videos and I'm curious about this point. Thanks!

[@Roelarex]

When everything is cut and mounted square and precise, the sideway movement is should not be a problem. However, I'm using a equatorial platform now, and that means the scope's base is not always parallel to the ground anymore, so I installed some Telfon sliders on the side to prevent the sideward movement of the mirror box.

[@hoshizoraclub_]

デカいなあ！ 大きな望遠鏡を持ち運べるのは、あなたの作業の丁寧さによるものでしょうね。私もあなたを見習いたい。

[@reidflemingworldstoughestm1394]

Probably not the most convenient optics for duck hunting.

[@markham_bd]

Amazing! But where is an image from this telescope?

[@Roelarex]

The telescope is designed for visual use only - not for photography.

[@nassteay6888]

Lekkah man je hebt mn subje

[@imspartacvs]

gorgeous happy hunting

[@haylspa]

great how about some pictures looking through the telescope!??

[@Roelarex]

The telescope is designed for visual use only - not for photography.

[@L.LGodwill]

Salute .

[@ibrahimkk6582]

What was the price of primary mirror?

[@user-dc2dv7gw5t]

Wat een briljant project weer! Heb afgelopen zomer m’n eerste telescoop gekocht, een 10 inch dob, maar dit moet toch wel alles wat je dacht gezien te hebben een nieuwe dimensie geven. Kijk je toevallig in Noord Nederland? Cheers

[@Roelarex]

Dank je! Mijn vaste waarneemstek is de locatie in het filmpje, maar ik ben zeker van plan om (weer) wat vaker richting het donkerdere Drenthe of Groningen te rijden met deze telescoop.

[@georgevarghese238]

What is the coast of the mirror.

[@MatheusFP104]

Any chance of publishing the design? Amazing piece of engineering.

[@eterenostalgia5088]

Here Italy, i have the telescope "Skywatcher heritage 130/650" with parabolic mirror from AMAZON for 188 euros (the price), small but high quality, Jupiter and Saturn sharp images.

[@Roelarex]

I have one too!

[@cchavezjr7]

Can you see color with the naked eye with this size mirror?

[@helthuismartin]

Prachtig gemaakt..Hoeveel kost nou zon Dobson tegenwoordig????

[@ultrametric9317]

How do you use this telescope in the Netherlands, which has the worst light pollution in Europe? There are some dark places left in France.

[@2010Edgars]

Fans will made vibrations. Better make non collision distance with fans.

[@Roelarex]

In theory, you're absolutely right. This was a test rig for the fans, just to see if it povides enough cooling. I can however not see any vibrations in the image, so I'll probably leave it this way...

[@jimpoop]

did you grind your own mirror? or where did you buy your optics?

[@Roelarex]

The primary mirror is made by Alluna Optics in Germany, the secondary mirror is from Orion UK.

[@WellingtonIronman]

The boundary layer fan, why not mount it on the side of the mirror blowing across so you don't obscure the mirror?

[@Roelarex]

I can understand what you mean, but unlike one would expect at first sight: the fan does not give any extra obstruction/obscuration of the mirror. The diameter of the fan is smaller than that of the secondary mirror and lies completely in its shadow. There is no negative influence on the image whatsoever, except some negligible effect on the diffraction spikes (from the thin mounting "vanes"). The benefit over (a row of) fans blowing from the side of the mirror is the more more efficient, symmetrical flow.

[@WellingtonIronman]

@@Roelarex oh ok! So the fact that the obstruction caused by the fan is present in the light cone ‘after’ being focussed by the primary actually doesn’t matter? Why do they bother making the primary mirror dot markings so small and unobtrusive I wonder?

[@Roelarex]

@@WellingtonIronman It has little to do with obstruction. The reason for the center markings being so small is because it makes it easier to get very precise collimation.. It's easier to exactly center the reflection of a tiny peephole in a very small ring than in a large one.

[@oalithgow]

Does that fan blows to the mirror or opposite?

[@MadawaskaObservatory]

Very nice telescope. Perhaps you might want to consider carbon rather than wood. It could reduce the weight by more than half. I hope its an open back cellular mirror, they are much stiffer and much much lighter

[@Roelarex]

No, unfortunately (as far as you can speak about "unfortunate" after a barnfind like that) it's a solid piece of glass. And a pretty heavy piece of glass too: 77lbs or 35kg... I do wish I could lift the thing without the bars or wheels, but like the Dutch say: "you have to row with the paddles you have". :)

[@taraswertelecki9586]

You came up with a very well designed and executed telescope, my 15-inch isn't nearly as nice. However, I hope you use a shroud over the truss be poles to keep dew, dust and so tray light out.

[@Roelarex]

For stray light the current baffling of the focuser and the light shield is 100% sufficient, but I indeed plan to make a shroud for this scope, mainly to keep the mirror clean and to prevent stuff falling on the precious mirror... Shrouds also helps the prevent your own body heat to cause air turbulence inside the telescope, so this is a good idea.

[@esotericist]

size matters

[@donaldkasper8346]

Obviously a telescope you would build with a CCD camera for the eyepiece.

[@RideAcrossTheRiver]

Why not an eyepiece?

[@planetman1983]

Awesome build. What is the total weight?

[@Roelarex]

Thanks! The total weight of the telescope is 70kg (154lbs).

[@planetman1983]

@@Roelarex What was the weight of the old telescope? I share a very similar story. I bought a 24" at 138kg and reconstructed it and the new telescope is 85kg total with wheels, handles etc.

[@Roelarex]

The original build was by Dieter Martini and its weight was 110kg (including the 35kg primary mirror). It was mainly the size what made the Martini uncovenient: it would not fit through the door!

[@planetman1983]

@@Roelarex Imagine mine at 138kg!

[@planetman1983]

@@Roelarex Didn't you use any rollers on the alt motion of the telescope? Just teflon on formica? The motion isn't hard? At azimuth I can see it is too soft.

[@MountainFisher]

I would have made the base out of aluminum. Everything aluminum especially the aperture, but then I'm an aerospace engineer and precision is my game. lol

[@RideAcrossTheRiver]

Metal shrinks when it cools.

[@MountainFisher]

@@RideAcrossTheRiver So does wood, but worse it expands in unaccounted ways when damp. The change over 25 inches at regular temperatures for aluminum isn't very significant for a scope and if it is going to be used in really cold temps just make it .010 too big where needed should be more than sufficient and as for the mirror it would be set on top of its base not into it. Mirror shrinks and expands too.

[@RideAcrossTheRiver]

@@MountainFisher Why we use steel and flakeboard.

[@MountainFisher]

@@RideAcrossTheRiver Flakeboard? I see plywood and steel is a metal too. All in all, although more expensive aluminum is half the weight and schedule 40 Al pipe would be more than sufficiently strong for the tubing. But one works with what one has. Not many have the skill to tig weld aluminum either without warping it.

[@RideAcrossTheRiver]

@@MountainFisher Sorry, I meant pressboard. I was thinking metal rings shrinking and expanding laterally would be a headache for collimation.

[@carlosgramajo6928]

YO APENAS PUEDO LLEVAR EL MIO DE 90 MM DESDE MI DORMITORIO EN EL PRIMER PISO HASTA LA TERRAZA, HERMOSO

[@mimcan70]

what is the bottom cost price for you except your labor ?

[@arwinholland.]

Ben uw Nederlandse? Misschien mag ik vragen als uw woon in Holland? Be dank

[@n0w3lly90]

Difficult to handle without a motorised mount. How fast does a celestial object disappear from view on that? I know from brother in law on a Meade 16" d Dobsonian that it isn't long, e.g. Jupiter speeding across the field of view and very difficult to track with a field of view measurable in arc seconds 😉

[@angle4cor]

Eyepieces with big FOV, like 100 degrees would be very handy here.

[@Roelarex]

A 12 year old kid with no observing experience whatsover could manually track M13 at 200x without any problems. Motorised tracking is of course the most convenient way of observing, but if a telescope moves smooth enough (a unmodified Meade Dob is not a very good example of this...), it should be no problem to follow an object even at very high magnifications. With this scope I find manual tracking at 500x very much doable. Using wide field eyepiece indeed helps a lot too. (Manual tracking AND sketching could be a challenge though, so I might build a platform in the future)

[@Guido_XL]

The idea of a Dobson is to have a light bucket available, without the hassle of an equatorial mount. As Roel pointed out, manual tracking is rather intuitive. A Dobson is not meant to replace a photography platform, for which we resort to equatorial mounts with motor tracking and a guiding camera/scope assembly on the main scope. I do not own a Dobson, as I started out with telescopes on equatorial mounts right away. But, I would love to have one, even if it weren't such an impressive one as Roel's. The joy of eyeballing galaxies and nebulae without first having to gather hundreds of exposures that are to be processed by software, must be astonishing.

[@NielssBohr]

You can just build an eq low profile platform. They did it in the 80s.

[@babaorume]

Where are Brad Pitt and Casey Affleck ?

[@Roelarex]

What do you mean? You got Brad Pitt right there. :)

[@fififilou9966]

👏👏👏👏👍👍👍

[@scott_meyer]

Here's a 70" home built DOB. kzbin.info/www/bejne/gaCoan5nhrCNlcU

[@funnyworld5482]

would be great having an idea of some of the images or something. I still don't get waiting for the car to drive down the road?

[@t3avelos]

3:09 Why only single persons can assemble the telescope? Does the telescope size make it incompatible with having a spouse, like "it's either me or "it" kind of situation?

[@AtlantaTerry]

Very funny. On the other hand, I'm still single.

[@Roelarex]

I never said ONLY single persons can assemble the scope. :)

[@t3avelos]

@@Roelarex thank you for clarifying. I had second thoughts for proposing to my fiancee after I saw your video.

[@drewm7071]

Cool video, but please speed up that intro. The pace and music feels like a funeral.

[@Acritas2021]

I admire you, but I don't envy you.