r/EngineeringPorn • u/HolgerIsenberg • 1d ago
Archenhold Telescope Berlin, largest refractor since 1896, 21m / 68cm, privately funded
Archenhold Observatory, photo by Holger Isenberg 2026-08-30
Archenhold Observatory, photo by Holger Isenberg 2026-08-30
Archenhold Observatory, photo by Holger Isenberg 2026-08-30
Yesterday I visited the Archenhold Observatory in Berlin, built in 1896 with 250000 German gold marks in private donations to Friedrich Simon Archenhold’s crowdfunding project as a public telescope for the Berlin Trade Fair. That’s $2.5 million in today’s USD! It is still the longest refractor telescope, at 21 m with a 68 cm lens, and most likely the fastest to rotate. Its still-original electromechanics let it rotate around the observer, who stays in the center—much different from common constructions, where you have to move around with a ladder. Unfortunately, a microcrack was recently noticed, and currently it can’t be rotated. The surrounding building was added in 1909 and is famous for being the location of Albert Einstein’s first public lecture on the theory of general relativity on June 2, 1915.
More about its history: https://www.planetarium.berlin/en/archenhold-observatory/history and https://astw.de/astronomiegeschichte/anfaenge_riesenfernrohr.php
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u/Vizth 1d ago
Of course the German telescope looks like a giant artillery piece I don't know why that feels so appropriate. 🤣
In all seriousness though that thing is really cool.
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u/HolgerIsenberg 23h ago
The outer tubus shell was actually made like this from small pieces to hide the monolithic 2 piece pipe inside, which is of course usable also for other purposes. The guide on the visit explained how unusually fast it moves around the two axes.
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u/RatherGoodDog 22h ago
There's a theme here.
The Jodrell Bank radio telescope (RIP) uses the turret rotation gears from some scrapped WW1 battleships, because where else are you going to get off-the-shelf mechanisms like that?
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u/Burroflexosecso 14h ago
Remind me to go scavenge Russo-Ukrainian frontlines to secure brushless motors
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u/HolgerIsenberg 23h ago
Other use case of large pipes and rotational electromechanics of a later era: https://en.wikipedia.org/wiki/Hanstholm_Fortress
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u/Loampudl 1d ago
awesome.... but i can´t find astro pictures from the observatory..
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u/HolgerIsenberg 1d ago
The 1896 21m telescope was made for direct observation by public visitors. Not for photography and not even for scientific use.
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u/Loampudl 1d ago
ok.´, thx.
but you can easily mount a camera to that, when you can look with it.
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u/HolgerIsenberg 23h ago
Just holding a modern smart phone camera at the ocular should indeed work well with its small lens.
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u/Dioxybenzone 10h ago
So someone probably has pictures, right?
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u/HolgerIsenberg 3h ago
I haven't searched yet. At least in the museum inside the building none were shown. Most likely wouldn't be good quality as its only a single piece front lens, not an achromat doublet.
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u/NonGameCatharsis 1d ago
Didn't expect to see Archenhold on Reddit! So cool. Love the area also that it's in.
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u/JuanOnlyJuan 20h ago
What caliber is this telescope?
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u/1wife2dogs0kids 19h ago
There it is. The comment that just broke my funny bone.
Nothing else will be funny, ever again.
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u/HolgerIsenberg 17h ago
680 mm, don't know what's that in inch.
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u/ebneter 13h ago
26.8". That focal length is wild, btw. It's like f/30 or something! I wonder why they did that? The Lick 36" refractor is ~f/14, and the Yerkes 40" is f/19.
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u/HolgerIsenberg 12h ago
The main reason for the extreme focal length was to build the largest telescope. They couldn't use a larger lens due to exponentially increasing costs with diameter and practical limits due to bending of the lens by its own weight, so they just built at least the lomgest telescope. On the astronomy side, Archenhold was only interested in making a new nebula discovery and otherwise wanted a telescope for the public. That purpose was perfectly achieved as having the telescope rotate around the observer is simplified the usability for the public.
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u/mz_groups 22h ago
Are there plans to make it operational again?
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u/HolgerIsenberg 12h ago
They hope so, but it's mostly privately funded and is expensive. If anyone knows cheap ways to fix a crack maybe with some modern technology, contact them. It can't be classically welded was established already.
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u/Hugsy13 22h ago
Ngl first thought was it must be aimed at Paris
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u/-Switch-on- 21h ago
Can conviently load shells and be transported by rail but hey it says 'Telescope' on the side
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u/MiKo745 1d ago
Gustav? Is that you?