Carl Zeiss Jena 12” Refractor (Griffith Observatory) Review

This is one of a series of slightly tongue-in-cheek reviews of famous observatory telescopes. Mostly, these reviews are the result of paying to attend a public or private viewing session. But the Griffith Observatory 12” Zeiss refractor is different: socialist astronomy and I love it – anyone can just queue up to view whatever object they’ve chosen for that night for free and without booking. Consequently, more people (millions, apparently) have looked through the Griffith Zeiss 12” than any other telescope ever. But it does mean you’re limited to a single object per night.

The Zeiss 12” refractor, along with a piggy-backed 9.5”, is in the left-hand copper dome of a grand Art Deco observatory building atop a hill in Griffith Park north of central Los Angeles. It’s a famous LA landmark and hugely popular with locals and tourists.

Griffith set up a pair of 11” Celestrons outside for viewing too and encourage people to join the shorter queues for those, saying the views are “comparable”. Well maybe. But I can look through a big SCT anytime; looks through big refractors are much rarer. So I queued early for the first place in the line.

I will hopefully extend this review whenever I get the chance to visit Griffith again. In due course, I’ll also write a separate article about Griffith Observatory in general (there’s lots of Astro/ stuff to see there and only the planetarium shows are payable).

History

Griffith Observatory was conceived when one Colonel Griffith J. Griffith had an epiphany at Mount Wilson Observatory, much like my own a few years ago. Just like me, he was profoundly affected by views through the 60” reflector (check out my experiences in the review here).

Colonel Griffith decided the World would be a better place if everyone could view the heavens through a proper big telescope. Griffith consulted various authorities including George Ellery Hale, the driving force behind many of the large US observatories a century ago, Including Mt Wilson, Yerkes and Palomar. As the result, he decided to establish a public observatory high above LA, equipped with a telescope of at least 12” aperture.

Sadly Griffith died in 1919 before realising his plans for the observatory, but he left a trust to fund it which duly purchased the a 12” refractor and mount from Carl Zeiss at Jena in 1931, on the advice of Hale’s instrument maker Russell W. Porter.

At that time, Carl Zeiss Jena was unrivalled for its ability to fabricate complete telescope systems, due to the theoretical work in optics of Zeiss’ partner Ernst Abbe, but also its expertise in optical glass (thanks to one Otto Schott) and in engineering too.

The 12” refractor and mount were built between 1931 and 1934 for the considerable sum (then) of $14900. Coincidentally, the first person to look through it is reputed to have been Mount Wilson astronomer Walter Baade, who was visiting the Zeiss factory at the time the 12” was being tested.

The 12” was shipped to the USA (thankfully well before the outbreak of war that would see the Jena factory destroyed by bombing) and installed at the newly constructed Los Angeles observatory in 1935, with opening night on the 14^th May. The first public session was on the first clear night thereafter - May 17^th 1935 - and Griffith have been holding them ever since, with over seven million orders of celestial view served.

The 12” Zeiss refractor is in the dome on the left, accessed from the roof via those curving stairs.

Getting There and Away

The observatory is open every day (except Mondays) until 10pm, with viewing from 7pm until 9:30pm on clear nights. Access is only via North Vermont Avenue off busy Los Feliz Blvd, most easily reached from I-5. If you’re driving, leave loads of time – the interstates are packed and slow around here.

After the mad driving below, North Vermont Avenue is a leafy, calm neighbourhood, with lots of walkers and runners up in the park.

There is only limited parking at the observatory and it’s expensive. It seems like there’s parking on the road near the top, but it’s for employees and they have staff checking all the time.

The good news is that you can park for free in a large car park on the left of the access road about 0.7 miles down from the observatory at the Greek Theatre. This had loads of space when I was there, even during the peak evening period when the observatory was heaving. But the climb, up a broad and well-lit sidewalk, just isn’t a problem if you’re fairly fit and seems safe on the way back at night too.

There are various bus options, if you fancy public transport in LA late in the evening (I didn’t).

At A Glance

Telescope	1931-34 Zeiss Jena 12” Refractor
Aperture	11.8 inches (300mm)
Focal Length	198 inches (5030mm)
Focal Ratio	F16.7
Length	~15 ft
Weight	4.5 tons

Data from Griffith Observatory.

Design and Build

Perhaps unsurprisingly, the build and grey enamel finish of the mount do remind of more modest Zeiss Jena scopes, like the Telementor.

The scope and mount are amazingly original and unmolested and in “excellent condition” according to the observatory, because (or perhaps in spite of) a 1991 renovation.

The piggybacked 9.5” refractor, added primarily as a guidescope in 1955, has a similar appearance, but different optical specs and was built separately, perhaps earlier. It was originally owned by a local amateur who had it mounted on his car for 20 years!

Optics

I can’t find much information on the optics, apart from that it’s a 300mm (not quite 12”, Zeiss were European and already metric) F16.7 achromat, presumably a Fraunhofer doublet. The smaller refractor has a faster 9.5” (242mm) lens at F14.8.

Tube

The cream metal tube has a smooth finish that lacks the numerous riveted sheets of earlier great refractors. The observatory’s own blurb says it’s “stress-compensated”, but I suspect that refers to the unusual mount configuration (see below).

Focuser

From historic images, it seems that the brass focuser is original.

The focuser drawtube ends in a kind of bayonet fitting, a bit like a DSLR camera lens, presumably to accept different eyepiece or instrument holders – sophisticated stuff from the 1930s. The drawtube has lots of travel and is about 80mm in diameter, but the visual back they fit into the bayonet seems only to accommodate 2” accessories now (not the larger ones that some observatory instruments use to get a wider field).

Mounting

The mount is an unusual design. Griffith describe it as an “offset-fork stress compensated equatorial”. The layout is a fork, but with the telescopes sitting above the declination axis, counterbalanced by a pair of weights on arms and a further pair of weights at right angles to balance the tube front-to-rear. The arrangement is much more compact than the massive German equatorial that typically supported large refractors of the time.

The fork on its RA axis is supported on a hefty casting that is attached to the concrete pier with large threaded bolts to allow it to be levelled. This casting has push-pull azimuth adjusters like most small equatorials. These adjusters are likely necessary to compensate for small shifts following earthquakes.

An image from 1935 suggests that slewing was electric via paddles from the start. These Zeiss-Jena logoed paddles are still in use, along with their original wiring from what I could see. The drive is by “crystal-controlled electronic tracking” and appears to be at least partially original, though it’s now encased in a glass box.

I did notice some drift over about half an hour between my goes at the eyepiece, but that was at 350x.

Originally, the mount was uncluttered, carrying just the 12” refractor; but it’s since accreted various other scopes, including the 9.5” refractor in 1955 and more recent Celestron 6” and 8” SCTs (the latter provided a live video feed whilst I was there).

Fork mount is of an unusual and sophisticated design.

Accessories

On the day I viewed, a 1.25” Celestron 14mm eyepiece was installed in a Tele Vue 2” diagonal. The operator reported that this eyepiece gave the best views of Mars (I’d seen him trying others), better than the available TV Ethos he said, though I can’t imagine why.

In Use – Astrophotography

Apparently, the big Zeiss was used to take many of the planetary images published in magazines back in its Fifties and Sixties heyday.

In Use – Observing the Night Sky

General Observing Notes

There is no entrance fee or ticketing – you just climb up one of the stairs to the flat roof area and wait in the queue which starts to form at about six-thirty. It’s much colder and windier up there, so don’t come in the shorts and t-shirt you wore for strolling down Hollywood Blvd that afternoon. I was comfortable in a puffer jacket and hat in January.

Entry to the dome is via a door (locked outside observing sessions) recessed within an entryway that has glass walls to view the telescope out of hours and a video screen for a live feed from the piggbacked Celestron SCT.

Exit from the dome is by a door on the other side, back to the top of the access stairs, so you don’t have to push past the queue: it’s a reminder that this observatory was actually built for mass public outreach.

Once inside the dome, you’re quickly climbing the broad hardwood stairs up to the eyepiece (there’s no need to negotiate a Lick-style ladder here). They warn you not to bump your head on the weights (it would be easy to do).

There’s nothing to stop you hanging back to ask questions or take photos after your turn and you’re free to walk back around and join the end of the line for another go (I did).

The operator set the 12” Zeiss on just the one object beforehand, choosing the eyepiece and getting it focused before opening. I’m guessing this is normal, due to the long queues and a short session (they stop the queue at 21:30 and end viewing at 21:45). I’m also guessing they usually choose the Moon, planets and maybe doubles, due to the light pollution and twilight start.

Note that the 9.5” refractor wasn’t in use, at least not during my visit.

Just queue and then view…

A live feed for those waiting in the queue – from an 8” SCT mounted on the Zeiss refractor.

Mars

On the night I was there, the chosen object was Mars, since it was a few weeks past opposition and still a respectable 12.4” in apparent diameter and high in the sky at 68° altitude. I wasn’t complaining as I love Mars and observatory sessions often sadly reject it as too difficult and lacking interest (I’m frowning at you, Lowell).

The image at 359x was sharp and clear, with the dark band comprising Mare Sirenum and Mare Erythraeum in the south and another dark area, including Mare Boreum, in the far north. There was no false colour marring the planet’s surface, but there was a wide and diffuse bright band of violet unfocussed light around it due to the achromatic optics.

This was my first look at Mars through a classic large achromatic refractor and something of a bucket-list experience for me.

Summary

I used to dislike LA thanks to the terrible traffic, maze of highways and some scary neighbourhoods. Then I discovered the magnificent and free spaces of the Getty Villa and Museum. The Griffith Observatory is more of that: park at the Greek Theatre and it’s completely free – the fabulous dusk views, the museum and galleries, but especially getting to look through their genuinely historic Zeiss refractor.

The whole experience was friendly too, with the scope properly set-up and focused and by a really knowledgeable and enthusiastic volunteer, who never tired of questions and interpretation. My only regret is not braving the traffic to do this on an earlier trip: don’t make the same mistake if you’re in LA for business or visiting Hollywood.

I hope to return on future trips and view another object or two, perhaps the Moon or Jupiter.

Join the seven million and take a look through Griffith’s wonderful 12” Carl Zeiss refractor: a must-do experience for anyone interested in astronomy and visiting LA.