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Ghost of the Argonaut

Posted by James Barnett   01/26/2007 12:00AM

Ghost of the Argonaut
James Barnett
Petaluma, CA
October 25, 2006

Orion 150mm Maksutov-Cassegrain
D = 150mm
F = 1800mm
f/12



Background

I’ve been an Orion watcher for a couple of decades. No, not the constellation. I mean the astronomy equipment reseller. I was living in Cupertino, California when Orion first opened its retail store in a local strip mall. The store is still there on the corner of Highway 9 (aka DeAnza Boulevard) and McClellan Road, but I am not, having moved away in the late 1980s. In January 2005, the original founder, Tim Gieseler, sold out to Imaginova, a multi-media educational products conglomerate.

The Orion of old was almost poetic when it came to branding and promoting new products. The “new” Orion seems to have lost some of its marketing spark. Remember Orion’s original 150mm Maksutov-Cassegrain, the “Argonaut”? It was a Russian-made scope, imported, re-branded, marketed and distributed by Orion. “Argonaut.” The very name conjures a sense of exploration and discovery. You, “Jason” and your crew, the “Argonaut” ply Homer’s wine-dark celestial seas in search of glittering jewels and arcane knowledge.

I dearly miss the days when manufacturers and resellers of astronomy products went the extra mile to create imaginative imagery for their products. Who can forget the Leonard Nimoy Celestron advertisement or the Meade “Research Grade” Newtonian advertisements with the bespectacled, lab-coat-clad model dwarfed by the equatorially mounted 12.5” in the background? Times and sensibilities change.

While Orion may have lost some of its marketing sizzle, it has recently gone back to its playbook and introduced a spiritual successor to the much-loved Argonaut 150mm MCT - the new (if unimaginatively named) “Orion 150mm Maksutov-Cassegrain”. The new scope is made in China by Orion partner Synta, and is also available from other Synta distributors worldwide under the “Sky-Watcher” brand. This review takes a look at Orion 150mm MCT and asks whether the scope delivers Orion’s typical virtues of bang for the buck.

Specifications

The Orion 150mm MCT provides a sturdy, all metal OTA, multi-coated optics, and unlike the Argonaut of days gone by, features an aluminized secondary spot on the inside of the corrector. That is the new 150mm Orion MCT is a Gregory-Maksutov. The old Argonaut had its secondary mirror mounted in a holder inserted into a perforation through the corrector (i.e., was a “Rumak-Maksutov” design). Also unlike the original Argonaut which had collimation adjustment screws for both the secondary as well as on the rear cell for the primary, the new Orion 150mm MCT has collimation bolts only on the rear cell casting of the OTA as shown in the photo, below.



The Orion product literature doesn’t say what substrate the corrector or primary mirrors are made of, nor does it promise any particular level of optical quality. The OTA features an integrated CG-5/Vixen-style dovetail bar. Overall the scope leaves an impression of workmanlike solidity. It’s pretty heavy for a 6” OTA weighing in at 12 pounds for the bare OTA alone. For comparison a bare 8” Celestron SCT OTA weighs only 4.5 pounds more and is much, much larger in dimension.

The 150mm MCT is currently available as a bare OTA for $599.95 plus shipping and handling, and is also available bundled with accessories and mount for quite a bit more. If you don’t have a spare star diagonal, finder scope and storage solution for the Orion 150mm MCT OTA, you can pick those up for extra cost from Orion too. For this test I added an $80 Orion 9x50 Right Angle Correct Image finder scope, an $80 Orion 1.25” Dielectric Coated Mirror Star Diagonal, an Orion Flexi Shield dew shade for $19 and a $45 Orion Padded Soft Case for the OTA. The “as tested” retail price for an Orion 150mm MCT set up as I’ve described would set you back $824; not a bad price for a ready-to-roll 6” MCT if it delivers quality optics. For reference that is approximately 25% less than a new Russian-made 6” Rumak-Maksutov with finder and dew shade.

For this review I mounted the Orion 150mm MCT on a Celestron CG-5 GOTO equatorial head and 48” Antares Pier. I also used Orion RockStable VSPs.

Under the Stars

Observing Conditions:

The observing sessions used to compile this report occurred over a period of several weeks and were conducted from my suburban front porch. Typical NELM at the zenith for this site is ~4.5. The east is inundated with sky glow from the local downtown 3 miles away, but my location faces almost due west so that the house blocks out the eastern horizon and the heaviest light pollution. The site is located at the inland opening of a long valley that cuts through the rolling coastal foothills to the Pacific Ocean some 20 miles distant as a crow flies. Seeing conditions are often sub-optimal as the rapid shifts from onshore to offshore wind flow create high altitude turbulence and often bring with it ground fog or haze. On the average night for this report, seeing and was 2.5/5 and transparency was 3/5. There were, however, a few exceptional nights where there was a dominant offshore flow and the humidity dropped to the bone dry “fire hazard” level. These nights were 4/5 for seeing and 5/5 for transparency.

Optical Performance:

Before discussing optical performance on particular classes of astronomical objects, there is one aspect of the Orion 150mm MCT I should get off my chest. The OTA takes a very, very long time to reach thermal equilibrium. At first I was storing the OTA in its case inside in the library, but found that the roughly 15-20 degree F temperature difference between inside and the observing site lead to cool down times of approximately 2 hours. Later I began storing the OTA in its case in a moderately insulated, partially subterranean garage that cut the night time temperature differential between storage location and observing site to 8-12 degrees F and shortened the cool down time to a more reasonable hour and twenty minutes.

The less well thermally equalized the OTA, the worse the optical performance. For example, after a half hour of cool down, images are very poor; stars don’t focus tightly, splitting moderately tight doubles like Epsilon Lyrae require atypically high powers and the resulting split is mushy, the lunar terminator appears as if it is submerged under flowing water and sharpness at very high powers suffers. All in all, if such a level of performance were all that this OTA were capable of, I would be giving it a poor rating.

Fortunately, when sufficiently cooled down, the scope is extremely capable. After an hour or more of cool down, a transformation begins to occur. After two hours, I was thinking “Why do I need a 5” APO again?” Suffice it to say that when properly cooled, the scope is capable of stunning performance and crazy-high magnifications. All observations for this report were recorded after ample cool down. Read on.

Luna

I spent two brief sessions, approximately one month apart, studying near the terminator of the waning waxing Moon. One such evening was had poor seeing and the other extremely good seeing. The poor seeing only moderately affected the performance of the scope on the Moon. The scope easily sustained 257x (7mm University Orthoscopic) with sharp focus and a wealth of fine, shadowy serpentine detail in the region of Vallis Schroteri. On the better of the two nights, sustaining 300x (6mm University Optics Plossl; 6mm Vixen LV) was a piece of cake with zero image breakdown, and 360x (5mm Celestron Ultima) was only just starting to soften up, but remained sharp enough to positively identify minute details in the same general region (near the location of the tiny crater Freud as shown in Rukl’s moon atlas).

Double Stars

From my light polluted locale and especially on moonlit nights that virtually rule out fruitful DSO hunting, I enjoy splitting double stars and discerning color differences in the pair. The 150mm MCT is no slouch. Epsilon Lyrae is pretty easy on even mediocre seeing nights at just 72x (25mm University Orthoscopic). I find that the 6” aperture is also considerably more effective than smaller apertures in detecting star color differences. In particular, Rasalgheti was a splendid, well-separated brighter, fiery tangerine and fainter snow white pair. The tight stellar points are very comparable to the images in 4 and 5” apochromats I own, but the long focal length gives the added bonus of decent eye relief using simple eyepieces at a given magnification compared to the faster apochromats. For example, the 150mm MCT produces 180x with a 10mm Zeiss Jena Orthoscopic with a very comfortable 8mm of eye relief, yet the Orion 100ED requires a 5mm eyepiece (5mm Celestron Ultima or 5mm University Orthoscopic) with half or even less eye relief to produce similar magnifications.

DSOs

6” is just enough aperture to get serious about DSOs from my light polluted site. In the contrasty 150mm MCT globular clusters actually have individual personalities and the brighter ones (say M92's brightness and brighter) show large degrees of resolution. Giants M13 and M22 show over one hundred distinct stellar points at 100x and just over (18mm University Orthoscopic and 15mm Televue Plossl). M2 and M15 show scores of resolved suns at similar magnifications. Even dimmer globulars like M28 in Sagittarius, M56 in Lyra and M71 in Delphinus show between tens and dozens of individual stars amid unresolved glow at higher powers (such as an 11mm Televue Plossl at 163x or a 12.5mm Takahashi LE at 144x).

As for nebulae and open clusters, M17 and M8 show modest amounts of structure with direct vision at relatively low magnifications (73x with a 24mm Takahashi LE). M20 is faint but directly visible, and its dark channels are hinted with averted vision in the 85-100x range. M27 looks like a big, slightly textured, pale rectangle with subtle curved indentations on the sides in a 14mm Meade Series 4000 UWA. M57 is a bright ghostly donut. NGC 6210 in Hercules shows as a moderately bright turquoise disc at 113x using a 16mm University Konig II. At 85x (21mm Pentax XL) the Wild Duck, M11, appears as a throng of 40 or so brighter white points surrounded by multitudes of fainter sparks. In a 15mm Televue Wide Field at 120x, NGC 7789 in Cassiopeia is a large circular haze speckled with scores of faint stars.

The long focal length makes for dark sky backgrounds and decent contrast. The downside of the long focal length is a relatively narrow true field of view. M31 illustrates these characteristics well. With a wide field (65 degree AFOV) 17mm Vixen LVW the Orion generates 105x and a true field of view of a little over half a degree. Using the 17mm Vixen the scope's excellent contrast makes tracing edge boundaries of huge diffuse ellipse a simple task, yet the small true field of view requires nearly 3 full fields to complete the observation. On smaller, dimmer galaxies like NGC 7331 the narrow true field of view is less of a liability, and the decent contrast makes short work of detection. Unfortunately 6 inches from a light polluted locations, even with good contrast, doesn’t allow much more than mere detection and verification of orientation on most galaxies.

Overall the 6" Orion MCT is a satisfying solar system and deep sky travel companion. The only negative optically is anecdotal. My first "real" telescope was a 6" f/8 Meade equatorially mounted Newtonian with optional manual RA override knob on the AC motor drive. It also happens to be the only other 6" scope I've ever owned. From memory, I believe that the images of these same objects (NGC 6210 and NGC 7331 in particular) were considerably brighter in the Newtonian than in this 150mm MCT. Granted that decades have elapsed between these observations, observing conditions with the Newtonian were under considerably darker, less polluted (light or otherwise) skies, and my eyes didn't have the mileage on them that they have now, but the impression remains.

Star Test and Collimation:

The star test on this scope is absolutely beautiful; among the best of any of my scopes, in fact. The diffraction rings are round, concentric (initially) and smooth on each side of focus. Altair, Polaris and magnifications in the 120x to 150x range were used for star testing on a couple of above-average nights during the evaluation period.

Collimation out of the box was near perfect, but near the end of the evaluation period a very slight deviation occurred. I’m not particularly rough on my scopes, but this OTA was mounted, un-mounted, bagged, and carried to and from storage over a dozen times for testing. Possibly I set the carrying case down “un-gently” on concrete while clearing shelf space in the garage for storage. In any case, I plan on adjusting collimation the next time I have this OTA outside. The misalignment is so slight that I wasn’t able to visually detect any deterioration of in-focus images on the objects observed. In fact, the second set of lunar observations (where I was pushing 360x) were done after the slight misalignment was noted.

Mechanical Characteristics and Finish Quality

Optical performance is by far the most important part of the OTA evaluation equation, but it is not the only material part. While telescopes are visual and photographic tools first and foremost, the best of them are also fine examples of industrial art and are a tactile pleasure to use. I have a Takahashi FS-78 that is as gorgeous to look at as it is to look through. It is almost jewel-like. I feel bad when I leave it out all night under a Telegizmos cover. The focuser is the smoothest I have ever used. The high level of fit and finish, mechanical precision and optical excellence engenders a level of near reverence unlike any of my other scopes. The feeling of respect transcends price. This particular FS-78 OTA cost me about the same as my Orion 100ED, and I have no such qualms about using the heck out of the Orion. At any rate, this portion of the report explores the aesthetic and tactile qualities of the 150mm MCT OTA.

Optical Surfaces:

From excellent star test and observing results, I would expect that the optical surfaces would similarly impress when looked “at” rather than “through”. The primary mirror is nicely aluminized with no evidence of pitting, roughness, edge chips or the like, and as you can see from the picture below, the corrector is nicely multi-coated, with no sleeks or coating flaws apparent.



The only “glitch” I experienced with the optics was the presence of a small blob of “stuff” on the optical surface of the aluminized secondary. It appeared to be either a bit of errantly applied adhesive from the secondary baffle or perhaps a small fleck of black paint dislodged from the baffle. In any case, a photographer’s squeeze bulb and a Starbucks extra-long “Venti” straw allowed me to dislodge the blob with a puff of air, leaving only a slight spec or two where it had been. No harm done.

Hardware Fit and Finish:

The paint quality on the OTA, rear casting and front corrector cell mounting and retaining rings is mediocre. The metallic grey paint on the OTA is semi-gloss, having an unfinished, gritty or sandy feel to it. Quality gloss enamel paint would have been a much better choice aesthetically. My normal “trick” for beautifying and preserving the finish on my OTAs is to apply an acrylic polish and protectant from Germany called “Klasse All-in-One”. Klasse works wonders on automobile finishes, boats, and as it turns out, painted metal surfaces on telescopes. I find that it greatly reduces the severity of fingerprints I get on my OTAs, and makes oils and dust easier to wipe off. On the Orion OTA, however, the rough paint quality stymied even Klasse.

The OTA includes a built-on Vixen GP/CG-5 compatible dovetail bar. The dovetail bar is painted black and is smooth-sided, having no indentations for either the main set screw or the smaller safety set screw on the mounting plate. Inevitably through extended use the surface of the bar will get scratched and marred with divots from the set screw tips. This will detract from the aesthetics but not from the utility.

The rear cell casting is well made aluminum, painted black. It is quite thick and heavy, and gives a sense of solidity and protection of the primary residing inside the casting. The paint on the rear casting is nicely applied without blemishes.

The metal components of the front cell affixing the corrector to main OTA aren’t as well finished. The lock-ring on the front side of the corrector (visible in the picture of the corrector above), appears to have an excessive amount of glue or “lock-tite” applied to it. There is a shiny swath of clear material along a 2 inch portion of the grove into which the lock-ring is threaded.

No beauty contest winner here, but rather a purposeful, utilitarian observing tool.

Focuser:

Okay, I’ll say it – I harbor grave suspicions about any moving primary focusing mechanism. There’s something counter-logical about belaboring the precise collimation of the fixed primary and secondary on a Newtonian or Dobsonian but accepting without question that a mechanical focusing system which moves the primary won’t have any adverse impact on optical performance of the system. Call it a bias.

More empirically based, however, is the fact this scope does exhibit some degree of mirror shift. Originally this unit displayed very little image shift while focusing. Maybe 8-to-10 arc seconds. By the end of the evaluation period, however, the magnitude of the shift grew to perhaps 12-18 arc seconds. To put this in perspective, this is less than half the image shift I observed on another Orion 150mm MCT and also less than half the image shift I experienced on a Celestron Ultima 2000 I used to own, so it’s not a bad case of the wobbles, but it is still a negative and an annoyance especially at high powers.

As moving mirror focusers go, this one is pretty good.

Mounting and Transport Ease:

As mentioned in the introduction, this OTA is relatively heavy for a 6” catadioptric OTA. The bare OTA (sans finder, diagonal, dew shade, etc.) weighs just over 12 pounds. For comparison the new 6” Celestron SCT OTA weighs just 10 pounds with a 6x30 finder. The compact OTA with its slight 15” length negates the extra weight when it comes to ease of mounting. The pier-mounted CG-5 GOTO used in this evaluation handled the fully equipped 150mm MCT with absolute easy. Focusing engendered quick-vanishing vibration even at very high magnifications. Slewing and tracking were error free and balance was easy to achieve. The 150mm MCT is much less taxing on this mount than a much lighter 4” f/14.4 Antares achromat I have. The 5 foot 7inch tube length of the nine pound Antares refractor OTA is a handful despite it’s low weight.

The small dimensions of the Orion 6” MCT make it a great road trip OTA. The scope nestled in its padded case with diagonal, finder and a couple of eyepieces stuffed into the side pouches takes up very little room in a trunk or cargo area of a vehicle, and can be manually carried long distances to an observing location without issue. The OTA, a few accessories plus a CG-5 class mount are all that are needed for a weekend or even a week of astro-friendly vacationing.


Conclusions

So there you have it. The Orion 150mm f/12 Maksutov-Cassegrain end to end, inside and out. It is not a scope for everyone. Above all it is not a scope for anyone who doesn’t have the time or patience to allow the dense little enclosed OTA to reach thermal equilibrium. Similarly, it is not a scope for fans of wide field Milky Way star cloud vistas. The 1.25” format coupled with the long 1800mm focal length make for an insurmountable sub-1 degree maximum true field of view limit. Insurmountable if you want no vignetting, that is. For anyone interested in viewing the moon, planets, brighter DSOs, and double stars and wants an affordable, compact, easily mountable and easily storable scope, this Orion is a worthy choice.

The Bottom Line:

WHAT’S HOT?

- tight, sharp, well defined images
- ability to handle high magnification on bright targets
- very dark sky backgrounds and great contrast
- eye-relief friendly long focal length
- well polished, coated optical surfaces
- compact, travel-friendly size
- easy to mount
- low price of the bare OTA
- built like a tank
- “guiltless” heavy use and abuse

WHAT’S NOT?

- excrutiatingly long cool down times
- sloppy fit and finish of some components
- some image shift during focusing; worse on some examples
- "unimaginative" product naming

Click here for more about this subject. -Ed.