RC Optical Systems (RCOS) 32” Ritchey-Chrétien Review
I recently spent a night observing with the Schulmann RC 32” at Sky Center on Mt Lemmon near Tucson at one of their public ‘Sky Nights’ sessions. I had lots of eyepiece time and was able to get a fair impression of this, perhaps the largest dedicated outreach telescope for visual use and one of the few that’s really modern (built in 2010).
I originally included some of this content in the review of the Sky Nights experience under the Travel section, here. But unlike many other big-scope observing nights, that program includes lots of other good stuff, so I've split out this review of the telescope.
At A Glance
RC Optical 32” Ritchey Chrétien
Central Obstruction (incl. holder/baffle)
Data from RCOS/Sky Center.
Design and Build
This large Ritchey Chrétien was installed in 2010, provided by the Schulman foundation and built by RC Optical Systems (RCOS).
RCOS were based locally (to Sky Center) in Flagstaff and mainly produced mid-sized reflectors optimised for scientific use (i.e. not really intended for visual), from 12.5” to 36” aperture. R C Optical have since been acquired by Deep Sky Instruments; this 32” is still available and appears to be their largest current model.
A few of RC Optical’s scopes were sold to individuals (I wish) but most in the larger sizes like this one were sold to smaller institutions such as university physics departments that wanted something better than the default 14” Celestron or 16” Meade. Lucky for us this one was acquired for an outreach program!
Like other RCOS products I’ve seen, this 32” is a beautifully made, all-CNC scope that has many premium features and is standing up well to lots of hard outreach use.
RCOS made two parallel lines of smaller Ritchey Chrétiens, one in solid carbon fibre tubes, the other in open or semi-open truss-tubes like this one. Surprisingly, the 32” does seem to be a turnkey product – the website shows images of at least two scopes that are subtly different, so they’ve clearly built others!
Promotional image: RC Optical Systems.
20” RC Optical for comparison.
Optically the Ritchey Chrétien Telescope (RCT) is a form of Cassegrain, a true reflecting telescope that uses neither a sub-aperture nor full-aperture corrector plate. The RCT became popular with professionals first (Hubble is an RCT) and latterly with amateurs, due to its wide field and round off-axis stellar images with lack of coma (though it still has a rather curved field).
Those characteristics, at a focal ratio faster than most Cassegrains (F7 for this 32” – faster than the smaller RCs which are typically ~F8) make the Ritchey Chrétien excellent for wide-field imaging.
The Ritchey Chrétien is harder to make well than the Classical Cassegrain, because it has hard-to-grind hyperbolic mirrors (a curve the Classical saves for its secondary mirror alone, the primary being parabolic like a Newtonian).
The RCOS website suggests the main mirror is made of a low-expansion substrate, possibly Zerodur or Astro-sitall, figured to a minimum of 1/20th wave RMS.
Like other RC Optical OTAs, this one has a premium feel – in amateur terms, like a big AP refractor. All of the hardware is CNC-milled 6061 aluminium with carbon fibre truss-tubes.
The primary is centre-mounted, the secondary on a 4-vane spider. All Cassegrains are at risk from stray light and RCOS state the primary has a baffle tube with multiple knife edge baffles and the secondary a conical baffle.
The OTA houses multiple fans around the sides of the mirror cell for active cooling.
The petal flaps protecting the primary are remote operable.
For visual use, a Starlight Instruments Feather Touch rack-and-pinion focuser has been installed at the visual back. A remotely-operated secondary mirror focuser comes as standard and would likely be used for imaging applications.
The telescope also features an electrically operated instrument rotator behind the focuser with a 4” aperture – the red device you see below.
Massive fork mount is designed for remote operation of telescopes up to 40”. Also note the secondary mirror focuser.
Unlike other smaller RCs I’ve used, this one doesn’t sit on an off-the-shelf mount from the likes of AP or Paramount – it’s just too large and heavy! Instead, it has RC Optical’s own ‘Professional Series’ fork mount, designed for telescopes up to 40” and for remote or local goto operation.
This is a proper professional-class observatory instrument and the mount offers pointing to sub arcsec precision. It weighs over 5500 lbs (2500 kg).
It is capable of extremely rapid slewing, much faster than would be safe at a public session!
Most of our viewing was done with a 31mm Tele Vue Nagler giving a magnification of 184x and a field of view of 0.42°.
A Sky Watcher 150ED apochromatic refractor is fitted to give complimentary wide-field views.
For imaging sessions, an SBIG CCD is fitted at the visual back, see below for details.
In Use – Astrophotography
Unusually we were also allowed to try a spot of impromptu imaging through the eyepiece with our phones, something I’d never tried before for DSOs (it really only works with the latest phones that automatically stack images in low light).
My efforts were pretty crumby (hard to align my IPhone 13’s camera with the exit pupil in the dark), but the guide showed some truly magnificent snaps he’d taken: with a fancy CCD? Nope, with a Pixel 3 phone-cam!
You can book the Schulman for some serious imaging, whether on site or remotely. The website shows some stunning images taken through this telescope.
The CCD for these sessions is an SBIG STX with a KAF-16803 sensor measuring 36.8mm x 36.8mm at 4096x4096 pixels (16.8 MP). This may not be the very latest, but would have been a very high-end ($12000) camera when new.
In Use – The Night Sky
General Observing Notes
The viewing experience with the Schulman was amongst the best I’ve had on a public night. There was plenty of time at the eyepiece on both scopes and plenty of chairs to sit on in between. Adding to the comfort factor, the dome does have a small warm room.
Most unusually for a public viewing session, we were allowed to tweak the Feather Touch focuser for ourselves, something that really enhanced the experience for me. The focuser was easy to use, even for the inexperienced. Focus was very snappy with none of the mushiness you can get with larger apertures.
On its professional mount, slewing was simple, quick and precise, rock solid when tracking. You can just choose a new target from an on-screen sky map.
If you’re interested, the full list of objects viewed is as follows:
We looked at three bright stars, Deneb, Capella and Betelgeuse. This might surprise you if you’re a keen astronomer, but for the novices it seemed interesting and for me handy confirmation of the Schulman’s optical quality with a quick star test – all showed beautifully pinpoint Airy disks surrounded by perfect faint diffraction rings.
I might not choose an RC like the Schulman with a big secondary obstruction for planetary viewing, but under stable desert skies it worked fine, just as the 16” version did at Kitt Peak.
Our first views of Jupiter were during full daylight, but the view was surprisingly sharp, contrasty and detailed.
Later, during the dark-sky session, Jupiter showed a lot of cloud belt detail at 184x, with lots of tiny belts and storms. Even more impressively, the large aperture delivered much more colour – a range of buffs and salmon pinks – than usual.
Uranus showed a small blue-grey disk, but a couple of moons too, something of a first for me (a week later I saw more of them through the Struve 82” at McDonald).
This big bright and familiar open cluster actually looked best with the lower power and wider field of the Esprit 150ED, but the big aperture delivered richer star colours.
The Double Cluster
Through the 32”, the cores of the two clusters were just a fit in the field of view and showed many more stars than I’m used to with smaller apertures. Again the red stars showed off their colours.
The Rosette Nebula
I requested this, hoping the large aperture and dark skies might reveal more nebulosity than usual. Sadly it didn’t, though I’m not sure why. It’s often said that ‘aperture wins’ – not in this case!
The Andromeda Galaxy (M31)
This is another standard object for me, but the 32” revealed a small, dense and bright central core-within-the-core and dark lane differentiation, hints of the spiral structure, that are different from my views through any amateur-sized scope.
M1 The Crab Nebula
This large and bright remnant of a supernova in 1054 showed off its shape and some of the filigree internal structure you see in images in a way only larger apertures can.
M42 The Orion Nebula
This is a nebula that many of us observe and image regularly, but here it was different. The limited field just showed the central ‘box’ around the six dazzling main Trapezium stars and numerous fainter ones, but what a view, with prominent structure in the dark lane, clumps and festoons and knots in the nebulosity that looked almost 3D and which you only ever see in images. I could detect more than a hint of colour – pinks and greens – too.
An F7 RC isn’t what I’d choose as a large visual instrument. This is really a professional telescope naturally more suited to use with a CCD or spectrograph.
Nonetheless, at moderate powers at least (I didn’t have the chance to try higher powers) it surprised by giving really excellent views of most of the objects we looked at, even Jupiter. At over 9000ft under mostly stable skies, this kind of telescope works for visual in a way it wouldn’t under a thick and turbulent atmosphere (Sky Center quote average seeing for long exposures at one arcsec).
This is the largest truly modern telescope that I’ve looked through and a near-unique experience as such. The public session, despite including other activities, offered lots of quality telescope time for a very modest price.
A private session – whether to just slew through your visual DSO bucket list, or concentrate on getting a set of superb frames for just a few – would be an amazing astronomy experience, though an expensive one.
The public viewing night described here was $85 in early 2022. Current prices for private sessions are $1500 for a full night of either viewing or imaging. A half night of remote imaging is currently $400. Check the Sky Center website for latest prices and availability.
The Schulman 32” RC is likely the largest telescope commissioned and dedicated to outreach. It’s a unique opportunity to experience a really modern observatory-class instrument. Public nights are amazing value.