By Ed Ting (Content Creator at compare.edu.vn – Expert in Physical Phenomena Comparison)
Updated for English Speaking Audience & SEO: 2024
Alt text: Side-by-side comparison of 90mm Maksutov telescopes including Meade ETX, Celestron C90, and Questar 3.5 inch models, highlighting size and design differences in a telescope comparo.
Can a budget-friendly $200 Chinese Maksutov truly challenge the legendary Questar? In this comprehensive 90mm Maksutov Comparo, we delve into a detailed examination of the Meade ETX, Celestron C90, and the iconic 3.5″ Questar. For several months in early 2011, I had the privilege of having all three of these telescopes at my disposal, allowing for an in-depth side-by-side telescope comparo to determine if the more affordable options could rival the performance and prestige of the Questar.
Meade 90 ETX: The People’s Questar?
The Meade 90 ETX burst onto the scene in 1996, generating considerable excitement within the amateur astronomy community. Marketing materials at the time suggested that Meade had effectively cloned the revered Questar, but at a significantly lower price point of just $495. I vividly recall waiting lists forming at local astronomy retailers (back when brick-and-mortar telescope shops were more common). Eager eclipse chasers and individuals who had long aspired to own a Questar (myself included) eagerly lined up to purchase the ETX. However, some of the initial enthusiasm waned as the telescopes began to ship and users experienced the realities of the ETX. While the optical quality was generally commendable, the telescope was often hampered by a series of mechanical shortcomings. The drive bases exhibited excessive play, necessitating pre-positioning objects at the edge of the field of view to allow the drive to compensate for the slack. The focuser and axis locks felt廉价, and the awkwardly positioned 8×21 finder scope proved largely ineffective. A further issue arose over time with the secondary baffle adhesive weakening, as I unfortunately witnessed firsthand on my own ETX. Over several weeks, the secondary baffle gradually slid downwards, leaving a sticky residue on the silvered secondary spot. For me, $500 represented a significant investment in 1996, and I felt somewhat misled by the initial hype.
Over subsequent years, Meade implemented incremental improvements to the ETX, notably incorporating the Autostar Go-To system – a welcome departure from purely manual operation. They also refined the feel of the controls and, crucially, repositioned the finder scope further away from the optical tube assembly (OTA), making it actually usable. The price has also become more competitive; today, a complete ETX package, including Autostar and tripod, can be purchased for roughly the same $500 price tag as in 1996. Regular readers of this site will be aware that I’m not typically the biggest advocate for ETX telescopes. Yet, paradoxically, this hasn’t prevented me from owning multiple units. The current ETX in this comparo is my third, and it’s an original “RA” model. Due to failures in the drive fork bases over the years, or simply owner frustration, many ETX optical tubes have become separated from their original mounts. This is how I acquired this particular ETX, which now primarily serves as a spotting scope OTA. Rumors suggest that the ETX line is due for a significant update in the near future.
Alt text: Meade 90mm ETX Maksutov telescope optical tube mounted on a dovetail plate, illustrating its adaptability for different mounts in a telescope comparison.
Celestron C90: The Modern Value Champion
The Celestron C90, introduced in the late 1970s, established itself as Celestron’s entry-level telescope model. Unlike Celestron’s Schmidt-Cassegrain telescopes (SCTs) like the C5, C8, C11, and C14, the C90 adopted a Maksutov-Cassegrain optical design. It was offered in three distinct configurations, and they were not inexpensive for their time. My 1980 price list indicates the telephoto lens version at $235, the spotting scope at $315, and the fork-mounted astronomical version at $475. Crucially, these are 1980 US dollars. Adjusting for inflation using the CPI index from 1980 to 2009 (approximately a 2.33x increase), the astronomical version would equate to roughly $1106 in today’s currency. The original C90 suffered from the use of less desirable 0.965″ eyepieces, although an upgrade to a 1.25″ visual back was available for an additional cost. It also featured a largely ineffective 5×24 finder scope, positioned too close to the OTA, similar to the early ETX models. Original C90s are often viewed unfavorably today, and used examples can be found on platforms like Craigslist for under $100.
However, the modern C90 represents a significant departure from its predecessor. Under Synta ownership, Celestron has made substantial improvements in quality, and they have recently reintroduced the C90. The new iteration shares virtually no commonality with the original model. In fact, it visually and tactilely resembles a scaled-down version of Celestron’s larger Schmidt-Cassegrain telescopes. There appears to be no compromise on build quality or fit and finish in these contemporary entry-level scopes. In contrast to the ETX, which incorporates substantial plastic components (particularly in the rear cell), the C90 is constructed almost entirely from metal. While it may lack the refined elegance of the Questar, the industrially styled C90 possesses a robust and purposeful charm. It feels substantial and well-built in hand. The C90 represents exceptional value. The standard package includes two 1.25″ eyepieces (a 32mm and a 12.5mm), a 45-degree erect-image diagonal, and a canvas backpack-style carrying case. It is also equipped with a Vixen-style dovetail mounting plate, complete with small detents for set screws – a thoughtful detail. Depending on the retailer, a (somewhat flimsy) tripod with its own carrying case may also be included. The most compelling aspect is the price – often less than $200 shipped when purchased online.
Alt text: Celestron C90 Maksutov telescope package contents showcasing eyepieces, diagonal, carrying case, and optical tube, emphasizing its value proposition in a telescope comparo.
Questar: The Enduring Icon of Excellence
Founded in 1950, Questar has maintained an unwavering commitment to producing uncompromising telescopes for over seven decades. The original 3.5″ Questar may well be the longest continuously manufactured telescope model in history. Questars are favored by discerning eclipse chasers and travelers, individuals who demand the highest levels of optical and mechanical precision, and connoisseurs of finely crafted instruments in general (I’ve even seen Questars displayed as objets d’art in homes). They are undeniably premium instruments, with new models ranging from $4000 to over $6000 depending on selected options. Prospective buyers considering the used market should be prepared for a surprise. While some cost savings can be realized, used Questars, even older models, retain their value remarkably well and tend to be quickly acquired when available. If exploring the used market, it is advisable to seek out later versions equipped with the DC Powerguide systems.
Questars are characterized by certain unique design quirks. The 1.25″ eyepiece holder employs a somewhat unconventional mechanical arrangement. Earlier models, including the original versions (1950-1968) and early Brandon models (1968-1995), did not natively support the physical insertion of standard 1.25″ eyepieces (this is a physical, not optical, limitation). Modern Questars, manufactured from 1996 onwards, incorporate an adapter that enables the use of conventional 1.25″ eyepieces, as well as threaded eyepieces like the Brandons (Tele Vue also offers a compatible adapter, as shown below). While Brandon eyepieces are undeniably of exceptional quality, users may prefer to utilize their existing eyepiece collections. In most instances, using “non-Questar” eyepieces poses no issues, although occasional reports surface of certain eyepieces failing to reach focus in finder mode. Generally, sticking to reasonable eyepiece designs (avoiding excessively long or short focal lengths, or 1.25″/2″ hybrids) should prevent compatibility problems. The rear cell incorporates a control lever to switch between the standard view and a 1.6x Barlow-magnified view. In finder mode, magnifications of 4x or 6x are achieved with the standard Brandon eyepieces. Thus, with the manipulation of two levers, a single eyepiece can provide three distinct magnifications. This becomes second nature for dedicated Questar users, but required a period of adjustment for me.
Alt text: Eyepiece adapters for Questar telescopes, showcasing Questar brand adapter (left) and Tele Vue adapter (right) designed for using standard eyepieces in this telescope comparo.
Furthermore, the entire optical tube assembly rotates within a roughly 75-degree arc, allowing for convenient eyepiece positioning. Conversely, an arguably less user-friendly design choice is the diminutive size of the focus knob – the most frequently used control on the telescope. I found it challenging to locate by touch in darkness, especially when wearing gloves. The OTA itself, adorned with an embossed star atlas, functions as a sliding dew shield. Extending it reveals an inner section featuring a basic moon map. While neither map is particularly practical for observing, they contribute to the scope’s distinctive character. The Questar package includes three small tripod legs and an off-axis solar filter. The loaner unit I evaluated is a newer version equipped with the DC Powerguide, which connects to the base via a standard phone connector jack. While I encountered no operational problems, I wondered if the power cord entering the base from below might present clearance issues with certain mounts. The Powerguide drive is remarkably quiet – the quietest telescope drive I have ever encountered. Even with my ear pressed against the scope’s housing, the drive’s operation is barely audible.
My Questar test sample was generously loaned to me by the Physics department at Phillips Exeter Academy in Exeter, NH.
Alt text: The Questar 3.5 inch telescope nestled in its custom leather case, emphasizing its premium quality and portability in this telescope comparo.
Mounting the Questar has historically presented a consideration. Similar to the ETX, I found the included tabletop legs of limited utility, although some users have reported success with them. A dedicated Questar tripod is available, which functions effectively but adds substantial bulk and a $1350 cost, somewhat negating the scope’s inherent portability. Like the ETX, the Questar’s design may restrict pointing at objects in the southern sky when used on certain mounts due to the tube colliding with the base. For these reasons, “Duplex” Questar models, which allow detaching the OTA from the fork arms for use on alternative mounts, have gained popularity. For my observing sessions, I utilized a Tiffen (manufactured by Davis & Sanford) 4800 tripod and a Celestron CG-5 equatorial mount.
Not being a dedicated “Questarphile,” I am not fully versed in all the lore and anecdotal accounts surrounding the scope. However, there are numerous tales of observers discerning exceptional detail and resolving close double stars far beyond the theoretical resolution limit for a 90mm telescope. Regrettably, prevailing seeing conditions at my observing location did not permit me to validate such claims. I can unequivocally state that the Questar is an exquisitely crafted instrument. The manual slow-motion axis controls are remarkably precise and smooth. Extending the eyepiece results in a subtle rush of air and a soft popping sound. Running fingers across the rear cell’s controls is a tactile pleasure – the term “buttery smooth” seems almost inadequate to describe the feel of the adjustments.
Alt text: Close-up of the Questar 3.5 inch telescope showcasing its iconic design, high-quality finish, and compact form factor in this 90mm Maksutov telescope comparo.
Observing Comparo: ETX vs C90
I conducted observing sessions with the ETX and C90 over several nights in February and March of 2011. Both telescopes exhibited slight collimation errors, though neither was severely miscollimated, and no user-adjustable collimation mechanism is provided on either scope. The C90 appeared to exhibit a marginally cleaner star test, but optically, the two scopes performed comparably. Eyepieces employed during these sessions included the Tele Vue 32mm Plossl, 19mm Panoptic, 13mm Type 6 Nagler, and generic 32mm Celestron and Meade MA 25mm eyepieces. I observed a range of standard winter sky objects: M42 (Orion Nebula), M45 (Pleiades), Double Cluster, M31 (Andromeda Galaxy), Castor, Eta Cassiopeiae, M35, M37, M36, M38, and M1 (Crab Nebula). Visually, discerning a significant difference in optical performance between the two telescopes proved challenging. I was able to identify NGC 2158 near M35 and NGC 1907 near M38 with both scopes. Eta Cassiopeiae presented its distinctive wine-colored secondary component, and Castor was cleanly split at 96x magnification using the 13mm Nagler eyepiece.
In terms of purely optical performance, the two budget-friendly telescopes were essentially a wash. However, the mechanical aspects revealed more pronounced differences, and these differences significantly impacted the overall user experience. Despite my best efforts, I could never achieve true comfort when using the ETX. This was my third ETX unit, and each time I acquire one, I am reminded of the reasons I sold the previous one. The finder scope’s proximity to the OTA makes it nearly impossible to use comfortably at certain angles, especially for observers with larger heads. Furthermore, the finder’s crosshairs are excessively thin, rendering them virtually invisible against the night sky. Given the ETX’s 1250mm focal length, a functional finder scope is essential. Later ETX versions address this issue, but many older units like mine are still in circulation. The focus knob is undersized, and the scope exhibits excessive image shift. A common workaround for image shift is to repeatedly rack the focuser in and out to redistribute the grease. I performed this procedure extensively one evening while watching television. This did reduce the image shift somewhat, but a residual amount persisted, making high-power focusing on celestial objects frustrating, as the object would drift out of the field of view before precise focus could be achieved.
The C90 features a conventional eyepiece port extending from the rear of the OTA, allowing for both straight-through and diagonal viewing configurations. The ETX also has a rear port, but requires a $30 adapter for direct eyepiece use. Otherwise, users are limited to the integrated 90-degree flip mirror, which does not always return to precisely the same position. The C90 also feels more substantial and robustly constructed. While I never experienced any mechanical failures with the ETX, I instinctively treated it with more caution. Consequently, the C90 proved to be more user-friendly and became my preferred choice for casual observing when comparing these two telescopes.
Alt text: Ed Ting observing with the Celestron C90 Maksutov telescope, highlighting its ease of use and grab-and-go nature in this 90mm telescope comparo.
Observing Comparo: Questar Takes Center Stage
Similar to a sports team receiving a bye in the first round of a tournament, I deliberately reserved the Questar for later in the comparison, after spending time with the ETX and C90. I anticipated that once I began using the Questar, I would be less inclined to use the others. For the most part, this held true, although the situation proved to be slightly more nuanced than initially expected. Yes, I found the Questar to be superior, both mechanically and optically, to the ETX and C90. Image shift was entirely absent – truly impressive. Star testing the Questar was somewhat challenging. Observing both Procyon and Polaris, I detected minimal spherical aberration, but the optics appeared to be very slightly miscollimated. The degree of miscollimation was less pronounced than in the ETX or C90, but it was discernible. Intriguingly, the star test results improved when the Barlow lens was engaged.
The Questar’s finder mechanism is unconventional. Flipping a lever diverts the optical path through a small lens and out the bottom of the tube via a diagonal mirror. This configuration provides a low-magnification finder view (approximately 4x with the 32mm Brandon eyepiece) without requiring the observer to move their head from the main eyepiece. While conceptually elegant, this “open” finder design presents some practical limitations. Firstly, it is susceptible to dew formation – in humid conditions, the diagonal mirror dews over almost immediately. Secondly, lacking any form of baffling, the finder gathers considerable stray light. At best, this results in a brightening of the background sky, but in worst-case scenarios (when the scope is pointed near a streetlight), the finder view can be completely washed out. Thirdly, the finder on this particular Questar sample was not perfectly aligned with the main optical axis. This issue is exacerbated by the absence of crosshairs in the finder. Minor adjustments to the finder’s alignment can be made by manipulating four tiny cemented screws, but as the scope was a loaner, I refrained from breaking the cement seals. Compounding these issues, initial object acquisition still necessitates sighting along the tube, a task I find particularly cumbersome in observing. Therefore, despite my initial intention to evaluate all scopes “as is,” I ultimately resorted to temporarily mounting a Rigel QuikFinder on both the Questar and ETX. In the case of the Questar, this felt somewhat like adding a mustache to the Mona Lisa, but practicality prevailed.
Alt text: Solar observing with the Questar 3.5 inch telescope using a solar filter, demonstrating its versatility for different types of astronomical observation in this telescope comparo.
Once past the less-than-ideal finder, using the Questar is a genuine pleasure. I observed numerous winter objects, including M35, M37, M36, M38, M42, M1, Pleiades, Double Cluster, M31, Castor, and Eta Cassiopeiae. Experimenting with different eyepieces, I discovered a pleasant surprise – Tele Vue Plossl eyepieces are nearly parfocal with the Brandon eyepieces in the Questar. The integrated flip Barlow is convenient and frequently used, although it occasionally failed to seat perfectly, requiring re-engagement to ensure proper positioning.
While I successfully located all common winter and spring Messier objects with the Questar, deep-sky observing with a 90mm telescope is not inherently captivating. If faint deep-sky objects are a primary observing interest, none of the telescopes in this comparo will be particularly satisfying. After a few nights, I found myself reverting to my 12″ Dobsonian telescope for deep-sky pursuits. The 90mm Maksutovs in this comparo truly excel at lunar, solar (with appropriate filtration), double star, and planetary observation. Under favorable seeing conditions, lunar observing, for instance, is immensely rewarding, with the Questar capable of revealing numerous craterlets on the floor of Plato. The Alpine Valley crack is another challenging yet attainable lunar target. One shared characteristic of the ETX and Questar is their relatively short eyepiece barrels. When using a Barlow lens with their 90-degree eyepiece ports, a “shorty” style Barlow is necessary to avoid bottoming out in the holder (the C90 does not exhibit this issue).
I resolved several late-winter double stars, including Castor, Kappa Geminorum, Eta Cassiopeiae, and Algieba (Gamma Leonis). Prevailing seeing conditions limited me to resolving Algieba, at approximately 4 arcseconds separation, as the tightest double star over two months of observing. The Questar appeared to be operating well within its capabilities, but atmospheric seeing conditions did not permit pushing beyond its theoretical 1.3 arcsecond resolution limit.
One evening, I captured lunar images through all three telescopes. While not a rigorously scientific test, I endeavored to maintain consistent variables. The camera used was an Imaging Source DBK 21UA04.AS. All images were acquired at prime focus using the 90-degree port on the ETX and Questar, and straight-through with the C90. Images were captured within a 30-minute window on March 14, 2011. Gain, exposure, and shutter speed settings were held constant. Image processing was standardized using a saved profile in Registax. The image sets depict the Clavius region and Plato crater. The C90 images were flipped N/S and L/R in Photoshop to match the orientation of the ETX and Questar images.
Questar Lunar Images: The Questar delivered truly exceptional lunar images. Detail rendition is impressive, and image contrast is optimally balanced. The Plato image is demonstrably superior to those from the other scopes. The image quality was so compelling that I regretted not increasing magnification to attempt to capture the Alpine Valley crack.
Alt text: Lunar image of Clavius crater captured with Questar 3.5 inch telescope, showcasing high detail and balanced contrast in this 90mm Maksutov telescope image comparo.
Alt text: Lunar image of Plato crater captured with Questar 3.5 inch telescope, demonstrating superior image quality in comparison to other 90mm Maksutovs in this telescope image comparo.
C90 Lunar Images: The C90 images are characterized by brightness, high contrast, and vividness. These traits consistently manifested in the C90’s images, both visually and photographically. The C90 consistently yielded the brightest images (possibly due to modern optical coatings) and delivered the most immediate “wow factor” among the three telescopes. However, sheer “excitement” is not always the primary objective in astronomical observing. I felt that the Questar provided more realistic and nuanced lunar views. Additionally, the C90’s field of view is not perfectly flat, as evidenced in the Plato image.
Alt text: Lunar image of Clavius crater captured with Celestron C90 Maksutov telescope, exhibiting bright and contrasty image characteristics in this telescope image comparo.
Alt text: Lunar image of Plato crater captured with Celestron C90 Maksutov telescope, showing vividness but slight field curvature in this 90mm Maksutov telescope image comparo.
ETX Lunar Images: The ETX images, while usable, are less compelling than those from the Questar and C90. The ETX produced the dimmest images (more apparent during live capture than in the final processed images). For reasons not entirely clear, the ETX also yielded a slightly higher image magnification than the other two scopes, which could partially contribute to the perceived image dimness. Even considering this, the ETX performed adequately. However, when directly comparing detail rendition in Plato and the Alpine Valley to the Questar images, a noticeable loss of finer detail becomes apparent.
Alt text: Lunar image of Clavius crater captured with Meade ETX 90mm Maksutov telescope, displaying dimmer image and less detail compared to Questar in this telescope image comparo.
Alt text: Lunar image of Plato crater captured with Meade ETX 90mm Maksutov telescope, showing reduced detail and dimmer image in this 90mm Maksutov telescope image comparo.
The most revealing aspect of this imaging test is not fully evident in the static images themselves. The Questar was simply delightful to use. It not only produced the best images but did so with the least amount of effort. Focusing the Questar was significantly faster and easier than with the other two scopes. While the C90 exhibited no image shift, achieving optimal focus sometimes required slight back-and-forth focuser adjustments. I obtained good images from the ETX, but it required more effort and patience. Furthermore, observing Registax’s image processing revealed that the Questar yielded a higher proportion of usable frames per capture compared to the ETX and C90. On occasion, with the quality threshold set at 95% or higher in Registax, nearly 100% of the frames captured with the Questar were deemed usable. No other telescope I have used has approached this level of frame usability.
Let’s move on to a more engaging segment. Below are three sets of lunar images. Can you identify which telescope (C90, ETX, or Questar) produced each set? Camera settings remained consistent across all captures, capture durations were 15 seconds, and identical wavelet processing was applied in Registax. All images within these sets were acquired within a ten-minute timeframe. Based on the preceding observations, you should have sufficient clues to deduce the correct pairings. I presented this as a quiz to my astronomy club, and most members were able to correctly identify the scopes. Give it a try! Your judgment call awaits! (Answers are provided at the end of this article).
Image Set #1 – C, E, or Q? You make the call!
Alt text: Lunar image set 1 for telescope identification quiz in 90mm Maksutov comparo, challenging readers to distinguish image characteristics.
Alt text: Lunar image set 1 continued for telescope identification quiz in 90mm Maksutov comparo, prompting visual analysis for telescope differentiation.
Image Set #2 – C, E, or Q? You make the call!!
Alt text: Lunar image set 2 for telescope identification quiz in 90mm Maksutov comparo, encouraging readers to compare image qualities for telescope guessing.
Alt text: Lunar image set 2 continued for telescope identification quiz in 90mm Maksutov comparo, inviting readers to discern subtle differences in image rendition.
Image Set #3 – C, E, or Q? You make the call!!!
Alt text: Lunar image set 3 for telescope identification quiz in 90mm Maksutov comparo, testing readers’ ability to identify telescopes based on image output.
Alt text: Lunar image set 3 continued for telescope identification quiz in 90mm Maksutov comparo, challenging readers to finalize their telescope identification based on image characteristics.
Telescope Component Close-ups:
Alt text: Corrector plate close-up of Meade ETX 90mm Maksutov telescope, highlighting optical component in this telescope comparo.
Corrector plate, ETX
Alt text: Corrector plate close-up of Celestron C90 Maksutov telescope, showing optical element in this 90mm telescope comparo.
Corrector plate, C90
Alt text: Corrector plate close-up of Questar 3.5 inch Maksutov telescope, demonstrating precision optics in this telescope comparo.
Corrector plate, Questar
Alt text: Rear cell close-up of Meade ETX 90mm Maksutov telescope with remote focus cable attached, illustrating telescope mechanics in this comparo.
Rear cell, ETX (Remote focus cable attached)
Alt text: Rear cell close-up of Celestron C90 Maksutov telescope, showcasing rear telescope components in this 90mm comparo.
Rear cell, C90
Alt text: Rear cell close-up of Questar 3.5 inch Maksutov telescope highlighting controls for Barlow, finder switch, focus knob, and finder port in this telescope comparo.
Rear cell, Questar – Controls (Clockwise from top) – Barlow, finder switch, focus knob, finder port (small knob)
Conclusions: The Ultimate 90mm Maksutov Comparo Verdict
Optical Quality Verdict: Questar. Consistently, the Questar’s optics outperformed both the C90 and ETX in this comparo, both visually and photographically. While the Questar’s optical edge was sometimes subtle, discerning observers could consistently resolve finer details with the Questar that remained elusive in the other two telescopes. Despite being the oldest telescope in this test by a considerable margin, its 20+ year old optical coatings have demonstrably held up remarkably well.
Mechanical Quality Verdict: Questar. This is an unequivocal victory for the Questar in this telescope comparo. The Questar was a genuine pleasure to use. Its controls operate with silky smoothness, and the telescope encourages interaction. Image shift is entirely absent, and images snap into sharp focus in a way that the C90 and ETX simply cannot match. While commendable views and images could be obtained with the C90 and ETX, achieving optimal results required more effort and careful manipulation. This was particularly true for the ETX, which suffered from annoying image shift and an overall廉价 plastic feel.
Practicality Verdict: Questar. The Questar is simply a highly functional and practical instrument. Its portability is excellent, the Powerguide drive operates flawlessly and silently, and in a pinch, the included tabletop legs can be used. The ETX attempts to emulate the Questar’s concept of portability, but falls short in execution. The C90 ranks last in this category, as the included tripod is essentially unusable for serious astronomical observing, and a full-fledged equatorial mount is required to realize its full potential.
Desirability “Lust Factor” Verdict: Questar. Unsurprisingly, the Questar wins this category in this telescope comparo. Virtually everyone who encounters a Questar in person immediately experiences at least a fleeting desire to own one. During the review period, visitors to my home invariably gravitated towards the Questar. This level of desirability cannot be manufactured or purchased; it is intrinsic to the Questar brand. If you aspire to own a Questar, you likely already know it. Interestingly, some observers also expressed a degree of attraction to the diminutive ETX. Its compact size and appealing deep purple finish contribute to its charm. Its aluminum dust cap, in particular, feels incongruously high-quality compared to the rest of the scope. The industrially styled and utilitarian C90 ranked last in terms of “lust factor.”
Value Verdict: C90. The Celestron C90 emerges as the clear winner in the value category in this telescope comparo. It offers an embarrassingly capable telescope package for a remarkably low price. At the time of writing, they are practically being given away. If you have been contemplating acquiring a small Maksutov telescope, I strongly urge you to consider the C90 immediately, before they become unavailable or Celestron discontinues production. However, ensure you have a suitable mount for it (i.e., not the included tripod). The C90 is the surprise of this group, delivering a significant portion of the Questar’s performance at approximately 1/20th of the cost. The ETX, with its driven mount, might appeal to eclipse chasers seeking a portable observatory solution at a more accessible price point (for those who cannot justify a Questar). The Questar, predictably, ranks last in the value category, but Questar owners are not typically driven by bargain-hunting considerations.
Alt text: A collection of six Questar 3.5 inch telescopes at Phillips Exeter Academy, illustrating the enduring appeal and quality of the Questar brand in this telescope comparo.
After spending two months observing with these three telescopes, I thoroughly enjoyed the experience. I still harbor a desire to own a Questar, but the cost remains a significant barrier. Perhaps one day. Currently, if I were to spend my own money, I would opt for the Celestron C90. In fact, towards the end of the review period, I did precisely that (*).
-Ed Ting
(Note: Special thanks to John Blackwell, Paul Schroeder, Dan Smith, Larry Lopez, and Neil Rothschild for their valuable contributions to this article.)
(* Note: Subsequent to this review, two observers who had followed its progress independently purchased Celestron C90 telescopes. One unit exhibited decent performance, while the other displayed fair to poor optical quality. This suggests some degree of sample variation in C90 production. It is advisable to purchase new C90s from reputable retailers to ensure recourse in case of dissatisfaction.)
(Answers to image quiz: Set #1 – C90, Set #2 – Questar, Set #3 – ETX. Image brightness and contrast are key indicators. The C90 images are the brightest and most contrasty, the ETX images are the dimmest, and the Questar images are optimally balanced. How did you fare?)
Sidebar: Questar Eyepiece Compatibility Deep Dive
I am grateful to various Celestron C90 and Questar owners who have provided valuable insights and clarified specific nuances regarding these telescopes. The Questar, in particular, boasts such a long and rich history that certain model variations (not readily apparent to casual observers) have emerged over time. It is important to emphasize that owners of newer Questar models are highly unlikely to encounter any eyepiece compatibility issues. Even owners of older Questars will likely experience no problems. Eyepiece compatibility concerns should not deter anyone from considering the acquisition of these exceptional telescopes.
I received an informative email from Neil Rothschild, which is reprinted below in its comprehensive detail:
“Any Questar manufactured on or after approximately 1995 was delivered with the ‘black collar’ tapped for (and including) two thumbscrews and therefore can accept any 1.25” eyepiece as well as the Questar-Brandon eyepieces. Your friend likely bought a new adapter with the thumb screws although he could have had Questar update his eyepiece adapter as I mentioned previously, tapping it with a couple of 4-40 threads and adding the thumb screws. For example, my 1985 Q7 and my 1997 Q3.5 have the identical diopter adapter except for the thumb screws.
The original Questar’s diopter adapter for the Japanese oculars has a 1.25” outer diameter barrel. That diopter adapter can be removed from the Questar, attached to the Japanese oculars, and then those oculars can be used in any 1.25” slip fit adapter, including the modern Questar diopter adapter.
The original Questar has a 0.925” diameter axial adapter in the back of the control box. Circa 1964 Questar widened the port to 1 3/16” to fully take advantage of the available light cone. This new axial port is known as the “wide field version or wide field modification”.
All Questar diopter adapters, including the original for Japanese eyepieces, have 0.925” threads that match the 0.925” thread at the top of the control box used with the internal right angle prism. The diopter adapters simply unscrew from the top of the control box.
Therefore, any diopter adapter can be screwed into the original narrow axial port. The Japanese eyepieces have 1 3/16” threads so they can be screwed into the later/current 1 3/16” axial port of the wide field axial port models.
A modern Brandon can be screwed into an adapter ring in the Questar camera coupler so they can be used from the axial port in a straight through view. A dedicated axial port eyepiece adapter is also available. It accommodates threaded Brandon eyepieces or standard 1.25” slip fit eyepieces (with thumbscrews to secure the eyepiece) roughly similar in function to the modern diopter adapter but without the unnecessary fine diopter adjustment ring). Anyone with a modern Q would not care about compatibility with a Questar Japanese eyepiece unless they were fortunate to find one loose. I suspect they are fairly rare. Anyone with Questar-Brandon eyepieces can use standard 1.25” eyepieces, either loose in the diopter adapter or with a tapped adapter locked down with thumb screws.
Owners of earlier Q’s with Japanese eyepieces will generally purchase a modern diopter adapter (with thumb screws) that will take the new Brandon eyepieces as well as 1.25” eyepieces. They then have two choices when using their older Japanese oculars. They can swap the old diopter adapter in and out when they use the Japanese oculars (which will focus in the finder of course). Or, they can leave the new diopter adapter in place and screw the old adapter into the Japanese oculars for a 1/25” slip fit. They then lose the ability to focus the Japanese oculars in the finder, but personally I would not want to swap those diopter adapters on a regular basis especially in the dark out in the field. It violates the fundamental Questar no hassle ease of use experience (IMO).
As you can see, for less than $100 any Questar ever made can be modified to handle modern 1.25” eyepieces as well as Brandon eyepieces.
You are probably aware that there are two styles of “Brandon eyepieces”. The “Questar-Brandon” eyepieces (marked as such on the barrel) have the threads that fit the Questar diopter adapter. Standard Brandons lack those threads. You can buy either style from Vernonscope but would want to specify Questar threads for that use. You can also purchase eyepieces from Questar or it’s dealers, of course.
The modern TV Plossls owned by your club members should come to focus in the finder. Note: I’ve never before seen the Questar and TV diopter adapters side by side. They are physically different heights. I’m wondering if the optical path is different, and if it is it would suggest that the two diopters might support different eyepieces in the finder mode???????????????????
Just as a reality check, the thin black disk (with the thumb screws) on top of the modern diopter adapter should turn. That is the “diopter” part, which slightly modifies the distance of the ocular to the finder mirror, allowing for adjustment of vision as well as distance. Once tightened they can stick and be quite difficult to get unstuck. It’s happened to me a couple of times over the years. If the school’s scope adapter was tightened to the point it was stuck and left that way for some time, it would appear to be immovable and could be quite difficult to loosen. I mention this as a possibility as to why you had trouble with the finder.
Any discussion of the features and accessories available for a Questar is quite complex. We have two “user groups” of Questar owners on the web. The oldest group is located at http://tech.groups.yahoo.com/group/Questar/. This group has its roots back to a Major-Domo mail list started sometime prior to 1995. The other group is located in a sub-forum on Cloudynights.com. Anyone interested in Questars really needs to be a member of one or ideally both groups.”
End 90 mm Mak Comparo
