Largest DOBs in Europe

[planetman83]

Hello guys,

I am seeing that there are too many big dobsonian telescopes in America but here in Europe I don't see any posts including big dobs. Why exactly is that? How large are the largest dobs in Europe? Are there any other companies that can recoat mirrors expect Orion Optics UK? How large are the largest mirrors that can be recoated here in Europe?

It is a question I am having for many years...

Edited October 16, 2020 by planetman83

[Peter Drew]

The largest Dob I've heard of in Europe is around 40".  VCSM in N. London can coat mirrors to at least 30" as they have done ours a couple of times over the years.     🙂

[Louis D]

Possibly because few Europeans have large enough trucks or vans to haul them to a dark site compared to the average American?  It's like hot air ballooning.  You need a large vehicle to haul a large, heavy object to where ever it is you're going to use it.  Same goes for towing a boat to a lake or the coast for some weekend fun on the water.

[bomberbaz]

Saw a video recently where a dob design (with a twist) had an 80" mirror i think. 

[PeterW]

There are a number of meter class scopes, france and Germany. Certainly challenges anything the Americans have!

Peter

[Captain Scarlet]

The trouble with very large aperture scopes is that the minimum magnification for a standard exit pupil gets too high, unless you go ridiculously fast.

For example, 1000mm aperture f/3 with an exit pupil of 7mm implies minimum youthful magnification of 143x, and even higher if you’re older! That completely rules out extended nebulous objects which is what the large apertures are primarily aimed at.

M

[Louis D]

26 minutes ago, Captain Magenta said:

For example, 1000mm aperture f/3 with an exit pupil of 7mm implies minimum youthful magnification of 143x, and even higher if you’re older! That completely rules out extended nebulous objects which is what the large apertures are primarily aimed at.

Large objects, yes, but not globular clusters, planetary nebula, planets, double stars, compact open clusters, galaxies, etc.  300x to 700x is quite usable in the desert Southwest and on Florida's Gulf coast.  This is similar to the Canary Islands by my understanding.  However, it's quite difficult to drive a giant Dob to the Canaries.  Perhaps there are other areas in Europe with dark skies and stable seeing conditions?

[Captain Scarlet]

11 minutes ago, Louis D said:

... Perhaps there are other areas in Europe with dark skies and stable seeing conditions?

Fair enough re all those other types of targets.

Regarding European really dark sites, there are not many easily accessible. I’ve based myself partly in extreme SW Ireland which is one of those places, and a big dob is on the wish list. I have a 12” but hanker for twice that.

M

[Nyctimene]

A 42"/107 cm Dob in Germany :

http://www.herzberger-teleskoptreffen.de/news/ds06.php

(English text and pictures in "Dobson-Teleskop")

Stephan

Edited October 16, 2020 by Nyctimene

[jetstream]

Not exactly on topic but I've been looking for a used 30"+ piece of pyrex for a while now. And yes it will be in the f3's in the end.

[Alan White]

Possibly down to available storage space, seeing conditions, dark skies and available money.

[estwing]

I would  love to go bigger but the amount of time I get out with 18" doesn't justify spending 8k+...

[PeterW]

Eastern Europe is reckoned to be quite good, the Liverpool 30” lives in Hungary I believe. I think the final frontier would be binocular ultrafast with 7mm exit pupil, like Mel Bartels is currently working on. Two eyes really are better to an one and fast improves the richness of the view. Possible for 12”+. Of course those of us on the Dark Side end up going in the other direction... my latest optic had a focal length of 16mm and the views were great!

Peter

[PeterW]

https://www.bbastrodesigns.com/Largest Amateur Telescopes.html Worldwide, but Mike Lockwood just made a 45” f3.75, where it is we don’t know!

Peter

[Marvin Jenkins]

I am pretty sure I have seen a picture of two 20” dobs joined together side by side like a bino viewer. I vaguely remember it being Italian.

Marvin

[bomberbaz]

Thgis is the one i was on about although it is a 70" mirror and not 80"

https://blog.nationalgeographic.org/2013/11/08/worlds-largest-backyard-telescope/

[estwing]

2 hours ago, Marvin Jenkins said:

I am pretty sure I have seen a picture of two 20” dobs joined together side by side like a bino viewer. I vaguely remember it being Italian.

Marvin

Think that was two 18" with john Nichol mirrors 

[Ships and Stars]

On 17/10/2020 at 10:14, PeterW said:

Eastern Europe is reckoned to be quite good, the Liverpool 30” lives in Hungary I believe. I think the final frontier would be binocular ultrafast with 7mm exit pupil, like Mel Bartels is currently working on. Two eyes really are better to an one and fast improves the richness of the view. Possible for 12”+. Of course those of us on the Dark Side end up going in the other direction... my latest optic had a focal length of 16mm and the views were great!

Peter

 

21 hours ago, Marvin Jenkins said:

I am pretty sure I have seen a picture of two 20” dobs joined together side by side like a bino viewer. I vaguely remember it being Italian.

Marvin

I've been thinking about binoscopes since this summer as an alternative to a ridiculously large dobsonian, with the added benefit of stereo vision and a much wider FOV. If another 500p come up for sale, I'd serious consider trying to pair them up. Based on prevailing 1.4x theory of increased aperture equivalent, a 500p binoscope would be something like the equivalent of a 28" dob, but with only 2000mm focal length instead of 2850mm. I could still easily fit two of them in my van plus the mounting arrangement. The downside of course is collimation and complexity of design mating the two, but for the money, there's nothing even close to what that would be capable of. I'm not into night vision yet, that would be a later add-on years down the road for the ultimate semi-portable set-up. 

[Merlin]

Is there really much point in having a monster 'scope, if we are not doing research projects?

[Barry-W-Fenner]

This picture should put it into perspective, my 8" dob, next to my huge 30" monster 😁😁😂

[jetstream]

55 minutes ago, Ships and Stars said:

I've been thinking about binoscopes since this summer

From what I see the binoscope guys share information and technology across the globe- some much needed prisms etc being made in Europe. I too want a binoscope, a very fast binoscope but the cost .....

https://www.bbastrodesigns.com/30/30 inch binoscope.html

[jetstream]

http://arieotte-binoscopes.nl/Binocular Summation Factor revised 2019.pdf

Read this...

[Ships and Stars]

11 minutes ago, jetstream said:

From what I see the binoscope guys share information and technology across the globe- some much needed prisms etc being made in Europe. I too want a binoscope, a very fast binoscope but the cost .....

https://www.bbastrodesigns.com/30/30 inch binoscope.html

Yes when Mel Bartels says something is very challenging to make, it does kind of take the wind out of my sails. If another 300p flextube or 500p comes up for sale for the right price, I might have a go at it just because I already have one in hand. 

The 300p flextube would be fairly easy to mate up though because of the simple altitude bearing design. The fine adjustment part to collimate the two views is probably the crux. 

I may never make one, but I've decided that a 20" binoscope is more realistic for me than a monster dob and ultimately cheaper. I probably wouldn't tackle it unless we moved to a rural location however and I had a permanent observatory. Even my late night treks across the countryside have a practical limit! 😁 

PS I wonder why Mel says the secondary mirrors have to be larger?

Edited October 18, 2020 by Ships and Stars

[jetstream]

3 minutes ago, Ships and Stars said:

I probably wouldn't tackle it unless we moved to a rural location

Make me one too!

your gonna need a big binoscope to really out do your 20"...

From Mel

"I see dimmer stars. The difference is clear: go outside on a dark night and compare one eye to both eyes. Can the difference be quantified? The surface area of a binoscope's two mirrors equals a single mirror 41% larger. With binoscopes I see a magnitude gain of about 20% for stars, more than a single scope but less than naively combining the apertures. In other words, based on my observing experiences with binoscopes, I anticipate that a 30 inch binoscope will have the magnitude grasp of a 36 inch telescope. "

Edited October 18, 2020 by jetstream

[Ships and Stars]

Just now, jetstream said:

Make me one too!

your gonna need a big binoscope to really out do your 20"...\

From Mel

"I see dimmer stars. The difference is clear: go outside on a dark night and compare one eye to both eyes. Can the difference be quantified? The surface area of a binoscope's two mirrors equals a single mirror 41% larger. With binoscopes I see a magnitude gain of about 20% for stars, more than a single scope but less than naively combining the apertures. In other words, based on my observing experiences with binoscopes, I anticipate that a 30 inch binoscope will have the magnitude grasp of a 36 inch telescope. "

Just need the land, the house and a few other things first!! 😂

Land here isn't cheap either... it's nice to dream though. I think a 300p flextube binoscope would be a good starting point to learn from. I could pick up a £500 second-hand 300p, a couple of diagonals and a few bespoke, custom parts to mate things up. 

I make it sound so easy....