The Joy of the Maksutov Telescope

The author's superlative 7 inch Maksutov Cassegrain.

The author’s superlative 18cm f/15 Maksutov Cassegrain.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

A work began in December 2014.

 

Dedicated to Asbytec.

Among the catadioptrics, the Maksutov Cassegrain has justifiably earned a solid reputation as an excellent high resolution telescope. The Maksutov design combines a spherical mirror with a longer native focal length (slower f/3 relative aperture) than a typical Schmidt Cassegrain (f/2) with a weakly negative meniscus lens in a design that takes advantage of all the surfaces being nearly spherically symmetrical. The negative lens is usually full diameter and placed at the entrance pupil of the telescope (commonly called a corrector plate or meniscus corrector shell). The design corrects the problems of off-axis aberrations such as coma found in reflecting telescopes while also correcting for chromatic aberration. It was patented in 1941 by Russian optician Dmitri Dmitrievich Maksutov after a five year spell of careful ray tracing and prototype building, which culminated in the first working model produced in the autumn of the same year. He based his design on the idea behind the Bernard Schmidt’s camera, which used the spherical errors of a negative lens to correct the opposite errors inherent of a spherical primary mirror. Because the design utilises all-spherical elements, it greatly aids in mass fabrication.

Similar independent meniscus telescope designs were also patented in 1941 by Albert Bouwers (his 1941 concentric meniscus telescope), K. Penning and Dennis Gabor (a catadioptric non-monocentric design).A culture of secrecy during World War II kept these inventors from knowing about each other’s designs, but rightly or wrongly, the design was named after Maksutov and the rest as they say is history.

This design appeared commercially in Lawrence Braymer’s 1954 Questar telescope and in Perkin–Elmer designer John Gregory’s competing patent for a Maksutov–Cassegrain. Commercial use of Gregory’s design was explicitly reserved for Perkin–Elmer but was published as an amateur telescope design in a 1957 issue of Sky and Telescope in both f/15 and f/23 iterations. Most Maksutovs manufactured today are this type of ‘Cassegrain’ design (called either a “Gregory–Maksutov” or “spot-Maksutov”) that use all-spherical surfaces and have, as a secondary, a small aluminized spot on the inner face of the corrector. This has the advantage of simplifying construction. It also has the advantage of fixing the alignment of the secondary and eliminates the need for a ‘spider’ that would cause diffraction spikes. The disadvantage is that, if all spherical surfaces are used, such systems have to have focal ratios above f/15 to avoid aberrations. Also, a degree of freedom in correcting the optical system by changing the radius of curvature of the secondary is lost, since that radius is the same as that of the rear meniscus face. Gregory himself, in a second, faster (f/15) design, resorted to aspherization of the front corrector surface (or the primary mirror) in order to reduce aberrations. This has led to other designs with aspheric or additional elements to further reduce off-axis aberration. This type of Maksutov-Cassegrain’s high focal ratio and narrower field of view makes them more suitable for lunar and planetary imaging and any other type of observing where a narrow field high power view is just fine for resolving tightly packed globular clusters and double stars.

The elegant Questar 3.5

The elegant Questar 3.5

The Rumak
The Rutten Maksutov–Cassegrain (also called a Rumak or Sigler Maksutov) has a separate secondary mirror mounted on the back of the meniscus corrector, sometimes similar to the corrector/mirror holder configurations found in commercial Schmidt–Cassegrains. This provides an extra degree of freedom in correcting aberration by changing the curvature of the corrector and the secondary independently. Specifically it allows the designer to aspherize the secondary to provide a flatter field and slightly better colour correction than traditional spot Maksutovs, with less off-axis coma. Mounting the secondary on the corrector also limits diffraction spikes. This version is named after the work of the Dutch optical designer, Harrie Rutten.

Are Rumaks something to aspire to over the Gregory Mak? That’s something you’ll have to decide for yourself. To my way of thinking, a Gregory Mak is more than up to the task.

Some Historical Models

Perhaps the most iconic of modern telescopes is the beautiful Questar 3.5, a classic all metal, 90mm Gergory Maksutov that has changed very little in over half a century. While expensive, it is a great work of art and is still highly favoured by telescopists in the 21st century. The company also make larger Maksutovs (the Questar 7, for example) at (you’ve guessed it) much higher prices. Celestron was the first to respond to the high cost of the superlative Questar and marketed their orange tube C90 Maksutov in the late 1970’s for less than $500.

Optically, these were said to be quite variable, from mediocre to excellent. The big game changer came in the 1990s when Meade revolutionized amateur astronomy by introducing the ETX, first in the form of the RA, which had a built in clock drive and then shortly afterwards with the ETX EMC which featured full go-to capability. As an owner of the original ETX 90 RA, I can vouch for the excellent optics – on par with that of the far more expensive Questar 3.5. And though my unit is approaching twenty years of age, the mirror is in excellent condition, as are the coatings on the front corrector plate.

The venerable C90. Image credit; Celestron.

The venerable C90. Image credit; Celestron.

Shortly after the launch of the ETX 90, Meade introduced two larger instruments from the same family – the ETX 105 and the ETX 125. I spent a considerable time looking through the 125 and can vouch for the razor sharp optics on these units when conditions allow.
Meade also produced a 7inch (178mm) f/15 Gregory Mak as part of their highly successful LX-200 series of computerised telescopes which received very high praise from discriminating lunar and planetary observers who raved about their apo-like optics. These telescopes are now considered highly collectible classics from the late 20th century.

Celestron has recently revamped their venerable C90 in a neat black-tubed spotting scope. Costing less than $200, it provides excellent optics in an ergonomic package, eminently suitable for general nature studies and astronomy. It has to be one of the best bargains in the hobby today.

Cheap as Chips: the all new C90 spotting scope from Celestron.

Cheap as Chips: the all new C90 spotting scope from Celestron.

Despite these innovations it is arguably the range produced by Orion (USA) and SkyWatcher that has made most heads turn in the Maksutov camp in recent years. Following fast on the heels of the better established small companies, Synta churned out an exciting suite of Gregory Maks in the 90mm – 180mm range which could be purchased as complete packages including a mount or as optical tube assemblies. Over the last six months or so, I have been carefully evaluating an Orion re-branded version of Synta’s 180mm model – the telescope that has really opened my eyes to the tremendous versatility of the Maksutov design as a visual instrument.

She sure is purdy: the ETX 90 RA.

She sure is purdy: the ETX 90 RA.

 

 

 

 

 

 

 

 

 

 

Fit ’n’ Finish
The Orion 180mm Mak is no Questar 7 that’s for sure. But it’s got a few things going for it that makes it an exciting prospect even in comparison to the legendary Questar. For one thing, the corrector plate is made from the highest quality Schott optical glass and has the very latest in multi-layer anti-reflection coatings. The primary spherical mirror is over-coated too which will ensure its longevity over many decades if properly looked after. As a result, it may surprise you that it will yield slightly brighter images than older Questar 7s what with their more primitive magnesium fluoride based anti-reflection coatings.

The instrument is focused in a completely different way to a refractor and involves moving the primary mirror either closer or further away from the front corrector plate. I received the unit in perfect collimation after a long road trip and all of the components have remained in perfect alignment despite me taking the entire instrument apart to flock the inside tube as well as the long, slender baffle tube leading to the eyepiece. There is not many telescopes on God’s Earth that would allow such license. Remarkable!

The telescope equipped with tube rings and a 50mm finder tips the scales at under 20 pounds and is less than half a metre long, so it can be used on a light weight mount so saving quite a considerable cost to the user. This makes the instrument super portable, much more so than the equivalent refractor.

Maksutovs and Acclimation
Large catadioptrics can take some time to acclimate, especially if taken from a warm indoor environment to a chilly night outside. But this is not unique to this telescope genre; all large telescopes will struggle for a while before they stabilise in their new environment. Thankfully there are ways to ameliorate this. I’ve often taken my 17cm Orion Maksutov out from the warmth of my living room into my dry, unheated shed and after just a few hours it was delivering pinpoint stars in temperatures just a few degrees above zero. I’ve also had it working perfectly well in sub-zero temperatures.

The same instrument can be made permanently grab ‘n’ go by keeping it in the same environment while not in use. Others resort to active cooling using fans that blow cool air across the optical components. Some have suggested using cheap ice packs to create strong thermal gradients to draw heat out of the instrument. All these measures will accelerate the process of thermal acclimation. That being said, there are a few individuals (the ‘poodle pushers’), who have persisted in wilful scaremongering about these telescopes by asserting that they won’t acclimate in many locations. I was alerted to this after discovering that a seasoned observer located in La Union in the Philippines, who has done great work with a 6–inch Maksutov, over many years, enjoys diurnal temperature changes of ~10 degrees Celsius. This prompted me to do research into diurnal temperature variations and what I discovered was quite revealing; the vast majority (pick a location, any location LOL) of locations where humans live and observe enjoy annual diurnal temperature variations of the order of 10C, so telescopes of most any design will acclimate. At my location, these variations amount to little more than a few degrees (check out Glasgow climate and its average high and low temperatures throughout the year) and I have never had any significant issues with my 18cm f/15 Maksutov. The worst places, which exhibit diurnal temperature swings of the order of 20C or more, are located in deserts and at high altitude.

Maksutovs will work nearly anywhere on Earth. Laziness and ill-preparedness have prevented many from discovering this. Others have been led to believe that they won’t acclimate. But I wonder if this is the result of cultivating an elaborate lie; a  bad meme spread on tinternet. I remember a well known American astronomy couple who boldly wore T-shirts emblazoned with a  ‘No to Catadioptrics’ logo. How myopic is that? How misleading is that?

Recurring interest in the Maksutov Design over the Decades
There seems to be a recurring interest in this design, its elegance of form, extreme portability for its aperture, rigidity of the various components in the optical train and so on and so forth. It’s interesting that three of the leading amateur ‘scope makers in the USA; TEC, Astrophysics and D&G have offered Maksutov or classical cassegrains to their customers. The leading UK telescope manufacturer, Orion Optics, Newcastle under Lyme, England, also produce their own versions – the OMC series;

Zeiss too seem to have offered Maksutovs for amateur astronomers back in the day. And then there are the various incarnations from Intes and Lomo etc etc.

Why do you suppose the Maksutov Cassegrain has garnered such interest from these opticians of skill? The reasons are clear to me. The extreme portability and ergonomics of the design is a major plus of course, and the not too inconsiderable fact that they serve up images midway between an SCT and a fine refractor, has led leading telescope makers to maintain an interest in building them and bringing them to market.

Having said that, in independent bench tests, the mass market Maksutov fairs very well in comparison to custom designed units made by leading telescope makers.

I found one test on Mr. Rohr’s website, where he evaluated the 6 inch SkyWatcher model;

Herr Rohr also evaluated a 8-inch TEC Mak.

You can see two further  tests on the SkyWatcher 180 Maksutov here and here.

Not bad quality from the mass market Chinese Mak eh?

That kind of quality is more than enough to achieve  superlative visual results as is showcased in the next section.

A Case Study; Asbytec’s Work with a 6 inch Orion Maksutov

As mentioned previously, dedicated observers using the Maksutov have produced some very high quality work. Based in La Union in the Philippines, Asbytec has faithfully used his 6 inch Orion Mak over several years to produce an excellent portfolio. Many of his drawings have appeared on the online telescope site Cloudynights. His work highlights the high resolution capabilities of the Maksutov under good seeing conditions and his trained eyes have really pushed the envelope in terms of what can be seen. My own but less extensive work with its larger Orion sibling dovetails very nicely with his.

Jupiter

Jupiter. Image Credit: Asbytec

 

Mars

Mars. Image credit: Asbytec

 

 

 

 

 

 

 

 

Saturn

Saturn. Image credit: Asbytec

The Eskimo Nebula

The Eskimo Nebula. Image credit: Asbytec

 

Elongation in 72 Pegasi. Note the angular separation!

Elongation in 72 Pegasi. Note the angular separation! Image credit: Asbytec.

 

 

 

 

 

 

 

 

 

 

 

 

 

 Imaging with the Maksutov

The long focal length of the Maksutov makes it especially suited to lunar and planetary imaging. The majority of other instruments require powerful Barlow lenses or Powermates to boost the f ratio to about f/20 ( generally considered to be the sweet spot for imagers) but with many Maks having relative apertures of 15 or so, little in the way of auxiliary amplifiers are needed to get to that optimal imaging speed. Richard Garrad, an imager from Utah, USA, has used his Orion 180mm Mak to great effect capturing detailed images of the bright planets and the vast lunar regolith. You can see examples of his work and gain an appreciation of the excellent resolution and light gathering power of the same instrument here.

Notes from the field

To get the best performance out of the telescope, I flocked its main tube as well as the long baffle tube connected to the primary mirror. This resulted in a small increase in the contrast of daylight images (which can ‘flood’ the tube with off axis light) as well as on bright objects like the Moon and bright planets. After testing a few different types of diagonals, I came to the conclusion that a good quality prism diagonal was preferable to its dielectric mirror based counterpart. Well made prism diagonals seem to do a better job curtailing stray light and improve contrast. That said, the model used was not one of the expensive prism diagonals but a no frills 1.25” Celestron model # 94115-A, which I consider an excellent value in today’s market.

Like the classical refractor, one of the great joys of the Maksutov telescope is that it can be used with fairly inexpensive eyepieces owing to its high f ratio. Simple Plossl and orthoscopic  eyepieces give excellent edge to edge performance in this telescope so the user will not incur a large monetary sacrifice in using the instrument. For low power work,  I elected to use a SkyWatcher 32mm Plossl delivering a power of 84x and a half a degree field. For higher power applications I employ a 24-8mm Mark III Baader Hyperion zoom, the performance of which is excellent.

One might think that such a large aperture telescope would be unsuitable for nature studies but I found it to be excellent in this capacity. What makes it so versatile in this respect is its low mass and tremendous back focus. You can focus on flowers just a few metres away and examine their glory at powers up to 300x. I found this to be quite an enjoyable pastime during the summer months. Without the addition of various extenders etc, you simply can’t do that with a refractor of the same size.

Comparing its double star efficacy with that of my fine 5” f/12 achromatic refractor, I found the Orion Maksutov to be noticeably superior at ferreting out sub arc second pairs such as the 0.9” Lambda Cygni and on one occasion, a big surprise from the star O Sigma 507 (RA 23h 49 min, Dec +64 degrees 54 min). The A/C components (mag 6.8/8.6), separated by about a Jupiter diameter and arranged roughly north-south, were easy pickings at low power but I was more interested to see what happened to the primary as I cranked up the magnification to 340x. So I swung the system to the east end of the field and let the vibrations settle down. To my sheer amazement, I glimpsed (often for several moments at a time) the secondary (A/B; mag 6.8/7.8) just (and only just) touching the primary, and extending away to the northwest! I repeated this several times within a few minutes to make sure I wasn’t seeing a diffraction artifact. As I have described elsewhere in my double star surveys, it looked for all the world like a “a tiny little snowman in the sky” morphed time and again by the vagaries of the atmosphere. Now, my records show that A/B is currently of the order of 0.7 arc seconds apart! This is truly an extraordinary result, as the components were not merely elongated but very nearly separated to my average eye. Clearly, the Maksutov was operating real close to its theoretical limits (so far as is known conventionally). Let me tell you you’ll struggle to get this kind of performance out of  the finest 6 inch refractor money can buy!

This is a new ‘personal best’ for me. If anything, it shows that I can go beyond the 0.9 arc second barrier under the best conditions which were clearly on offer at this location (Torphins in Northeast Scotland) on this evening. That said, my notes show that I already enjoyed excellent seeing here before, albeit using smaller instruments.

In other tests, I turned both the Orion Maksutov and my high quality 5″ refractor on Psi Cassiopeiae. The primary is a 5th magnitude K spectral class star and just east of it lies the faint magnitude 9.1 and 10.0 (C & D components) separated by 2.3”. Looking first through the large Maksutov, I could see the exceedingly faint pair at 170x. The challenge here is that the C and D components are both very close and very faint and the bright orange glow from the primary right next door doesn’t help. In comparison, the 5 inch refractor really struggled. I convinced myself that it was doable – but only just! Thus, there was a clear performance difference between the instruments here.

The faint companions to Psi Cassiopeiae as sketched by the author.

The faint companions to Psi Cassiopeiae as sketched by the author.

The same is true of its lunar and planetary performance. If fully acclimated and under good conditions, the Orion Maksutov will comfortably outperform the 5 inch refractor. This was made apparent by studying the craterlets on the floor of Plato. The largest – A, B and C – can be seen in the 5-inch refractor but are better defined in the larger Maksutov. The D craterlet, which was distinctly seen in the Maksutov, was invisible in the refractor under the same conditions.

Preliminary tests comparing the views of the 5 inch refractor with the Orion Maksutov confirms that the latter can also resolve significantly finer atmospheric details on Jupiter than the former. The brighter image of the 170mm Maksutov allows greater magnifications to be pressed into service and under good conditions shows the true colour of ovals and barges.

Though opinions differ, like many larger aperture telescopes, I believe the Maksutov does benefit from the use of filters to bring out very subtle planetary details on the precipice of visibility. Blue filters (the 80A and 82A) are excellent for bringing out belt details, while the Baader Neodymium, Contrast Booster and TeleVue Bandmate planetary filters show great promise in enhancing low contrast details on the Jovian disk.

Some amateur astronomers consider the Maksutov to be a rather specialised, high power, high resolution instrument, but that does not mean it can’t be put to good use as an effective instrument on deep sky objects. Truth be told, the vast majority of these objects are well framed within the smaller field of view of the Maksutov. In this capacity, I enjoyed many evenings studying the glories of the late summer Milky Way through Cygnus and Cassiopeia. Small open clusters are excellent targets for this telescope, as are globular clusters, owing to the telescope’s extra light grasp over a mid-sized refractor. The finest 5-6 inch refractor money can buy will not give you an image of M13 like this economical Maksutov. Everything is easier to see and better resolved. The Orion 18cm Maksutov is also a wonderful telescope for studying planetary nebulae. The views I had of M57, M27 and NGC 6826 were simply spell binding, exploiting the natural, high magnifications achieved by this instrument.

There is nothing preventing a determined observer from sketching larger swathes of sky than can be captured in the small field of view of the Maksutov. Here is a modest sketch I made of the Double Cluster (Caldwell 14) in Perseus. Because the maximum field of view presented by the 32mm Plossl is only of the order of 0.5 degrees, it cannot wholly capture both clusters in the same field of view. Both NGC 869 and NGC 884 individually span some 18’ of sky and are separated by about a Moon diameter (25’). Nevertheless I wanted to include both in the sketch, so I took to ‘stitching’ them together by moving the telescope slowly eastward from the core of NGC 869 towards NGC 884.

In this way the traditional limitations of the Maksutov’s small field can be overcome; in just the same way that imagers have done with their CCD cameras.

The Double Cluster in Peeus as drw by the authorr using his 17cm Orion Mak and a 32mm Plossl eyepiece.

The Double Cluster in Perseus,  as drawn by the author using his 18cm Orion Mak and a 32mm Plossl eyepiece.

Conclusions
The Orion 180mm Maksutov Cassegrain represents an excellent alternative to a medium aperture apochromatic refractor but is more closely akin to what you would expect from a long focal length classical refractor of the highest quality. The telescope will need some time to acclimate in winter, especially if taken from a heated inside room to the cool of the night air, but storing it in a dry unheated outhouse should alleviate any problems in this regard. Its ultra-compactness and relatively light weight for its aperture will allow you to transport the instrument safely in the back of your car to a dark sky site. In today’s market, where some amateurs obsess over high quality refractors costing a second mortgage to acquire, this magnificent, ergonomic telescope represents an exciting breath of fresh air! A telescope like this would have astounded an observer in my father’s time and he would have needed the wealth of a Sultan to acquire one of this quality. To think that one can get this kind of performance out of a telescope that cost just a few hundred pounds, is only half a metre long and weighs a mere 20 pounds, is a joyous revelation.

Why would anyone want anything more from a lightweight, ultraportable visual ‘scope?

Update: March 19, 2015

Having spent a fairly cold winter with this instrument, I am delighted to report that it has earned my deep admiration. Out of curiosity, a second time: I deliberately unscrewed the back, removed the flocking from the long baffle tube on the primary and reapplied fresh stuff LOL. When I put it back together, it still held perfect collimation as judged by a high power star test on two separate nights! This telescope is amazingly resilient to mis-collimation! Try it out for yourself! I think the rigidity of the aluminised spot on the secondary helps make this magic happen.

I have managed its ‘alleged’ thermal problems throughout this time and never once have I needed to resort to some kind of active cooling. I will re-state what I said previously; if the telescope is kept in a dry unheated shed, it is effectively in a permanent ‘grab n’ go’ state. Only the local seeing conditions will curtail its efficacy.

My family and friends have enjoyed some positively charming views of Jupiter, the Moon and a variety of deep sky objects with the telescope.

Here is a drawing of Jupiter I made on the evening of March 24 during a spell of fine weather.

Jupiter, as it appeared in the telescope at 190x on the evening of March 24, 2015.

Jupiter, as it appeared in the telescope at 190x on the evening of March 24, 2015.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

In addition, the telescope has continued to provide excellent views of tricky double stars. Challenging pairs such as Eta Geminorum (Propus), Iota Leonis and Eta Orionis have been successfully split under good seeing conditions.

Since first beginning my assessment of this large Gregory Maksutov, I have been made aware of two independent tests, both of which suggest that the optical quality of this telescope is very high.

You can see one such test here and another here.

I have had many opportunities to compare the views of Jupiter through my fine 5-inch f/12 achromat the 17cm Maksutov during bouts of fine seeing. The latter shows a good bit more detail than the long glass. My conclusions mirror this gentleman’s findings when he compared a 5″ f/15 refractor and a 7″ f/15 Intes Mak on the Moon and planets.

Cornelia Africana, my 180mm f/15 Maksutov Cassegrain.

Cornelia Africana.

 

 

 

 

 

 

 

 

 

I have named this telescope ‘Cornelia’ and she will remain in my stable, serving as a powerful and ultra-portable telescope.**

My Initial Exchange with the Public

And its Follow Up

Update: April 23, 2015

More Mak varieties have now hit the market.

Meade Instruments and Explore Scientific announce exciting new 6 inch Maksutov telescopes which were showcased at NEAF. Explore Scientific plan to shortly launch an even larger 8-inch model.

This is an exciting time for the Maksutov Cassegrain!

** The instrument was eventually sold on and the funds raised were given to a charity supporting the earthquake victims of Nepal in mid-2015. These days the author makes do with an excellent Skywatcher 8-inch f/6 Dobsonian.

 

De Fideli

44 thoughts on “The Joy of the Maksutov Telescope

  1. Neil, I have enjoyed your work and am thrilled you are enjoying your MCT as much as I am enjoying mine. That gives me a good gut feeling. I look forward to more of your work.

  2. Dear Norme,

    Thank you for your kind words of encouragement.

    Your long standing and enthusiastic work with a 6-inch MCT is proof enough that these instruments are capable of truly great things! I hope that this up-and-coming piece will help enhance their raport amongst a greater cross-section of amateurs.

    Regards,

    Neil.

  3. Neil, I forgot to tell you. One of the scopes I once owned and used was an MK67; the Russian-Intes built Rumak Maksutov. When that scope was thermally equalized, correctly collimated, and the night sky was steady; the contrast and detail it delivered were attention getting. I recall commenting on one such night how the Cassini division looked like a black ribbon wrapped all the way around Saturn.

    Otto

  4. Hello Otto,

    I’ve always been a fan of the Maksutov Cassegrain telescope for its sheer elegance of design. The 17cm Orion model I have is a great performer, pulling noticeably ahead of my 5 inch refractor on the best evenings. I love its ultra portability as well. I hope to use it extensively over the next few months to record details on Jupiter.

    Best wishes,

    Neil.

  5. Hi Neal
    Your articles and reviews are among the best i found….. and very authentic too 🙂 thanks for the great work you are doing…I have ordered a Celestron 127mm mak after selling celestron 6″sct and i hope i haven’t made a mistake as i was looking for some planetary and lunar scope and i hope it will be equally good if not better than the sct…according to my little knowledge the mak has smaller CO than the sct and it will be more sharper also…If you can shed some light pls let me know…Thanks in advance !!
    Sanjeev

  6. Hello Sanjeev,

    Thank you for your message and for the compliment. My apologies for the slight delay getting back to you; I had some students to attend to.

    Truth be told, I’m not at all sure whether the 127 Mak would be a better choice than the C6. They’d both have the same focal length (1500mm I think) but by screwing on a 0.63 reducer/field flattener on the C6, you could get a ~950mm focal length and so benefit from wider fields of view than could be achieved with the 127 Mak.
    The C6 has at least an inch greater aperture ( the 127 Mak would be working at about 120mm due to internal vignetting by the baffle) and even with its bigger CO, I feel it would potentially win out on virtually everything compared with the smaller Mak ( assuming of course, that the SCT is of reasonable quality). The C6 would thus be more versatile than the Mak.
    That said, I have heard many good things about the Mak; a lot of them sell in amateur circles because they’re very good. The Maksutov is an elegant optical design; one could look at one all day long and never grow tired LOL.

    Good luck with the telescope.

    Best wishes,

    Neil.

  7. Mr. English:

    Interesting piece on Maksutov-Cassegrains.

    One quibble though. Your statement that most places on Earth have no more than a 10C diurnal temperature variation is not correct in may local experience and perhaps more importantly seems to be a bit of a red herring. Isn’t the relevant temperature delta the one between where the telescope is stored and the nighttime low?

    Here in Tucson, Arizona, USA, we have a fairly consistent temperature delta of 15C. For American readers a 15C variation is quite large – like going from 50F to freezing (32F); windbreaker to winter coat. But beyond the question of whether 10C is accurate generally, many observers store their instruments indoors. Taking an instrument from a 20C study to a -5C winter night, that’s quite a difference.

    Lastly, in my tests with my scopes here outside of Tucson, the total delta seems to be less important than the rate of change from one extreme to the other. Some types of instruments seem to maintain their figure and remain freer of internal currents than others. My doublet refractors for example produce better quality images than do my C6, C90 or I-M 715 while cooling. Once the low is reached and the instruments equilibriate, image quality is comparable at like aperture and magnification.

    As a result, I generally avoid using my catadioptrics unless I have the time to let them cool adequately for my observing program for the evening. For deep sky objects, the ills of cooldown seem to be less impactful. For double stars, planets or Luna, cooldown seems to affect my catadioptrics disproportionately.

    On the other hand, as you point out there is no better way to achieve low cost, easily mountable aperture. Especially if you live in a climate with small temperature variations day to night or can store your instruments at ambient or leave them set up on a mount better still.

    – Carlos

  8. Dear Carlos,

    Thanks for your message.

    Pick a city, any city; lol.

    I think you’ll find the vast majority of places have diurnal temperature variations of about 10C, but there are exceptions, where the temperature delta is 15C, but that’s still not very large. Other exceptions are deserts and high altitude sites where folk don’t generally live.

    All along, I have repeatedly stated that storing the telescope in an unheated outhouse/shed that is close to the outside temperature will largely avoid thermal issues altogether. Works for me every time!

    In the end, laziness and deliberate scaremongering are the main culprits.

    Season’s Greetings to you and yours,

    Neil..

  9. Hi Neil – nice article/review. As a confirmed Mak-user, I enjoyed your thoughts here immensely. I myself have one of the 127 models, and have been greatly interested in these 180 models to satisfy my aperture fever. If I were to get one, it would be the Skywatcher model, which supports 2″ eyepieces. (Although I just got back from NEAF, and the VMC 200L has peaked my interest as well.) The maximum field of view would jump right back up to just over 1 full degree, the same as my 5″ Mak, and would allow viewing of both ends of the Double Cluster in one view as I view them now.

    I was wondering – you mentioned deliberate scaremongering in relation to Maks in general. In my travels throughout the different astronomy websites, Cloudy Nights being chief among them, I have encountered the same thing – a distinct bias against Maks for some reason. I find this incomprehensible when SCTs “suffer” (if that’s the right word) from the same “disadvantages” (if that’s also the right word) as Maks do – relatively long cooldown times, relatively narrow fields of view.

    They’re both closed-tube designs, so the cooldown shouldn’t be very much different between a Mak and an equivalent sized SCT. Plus, as you mentioned, the C6 has the same focal length as the 127 Mak, resulting in the same “limited” field of view – which I don’t find limiting at all. All but a half dozen or so of all the thousands of DSOs out there will fit in the 1.05 degree field of view of a 127mm 1540mm f/l Mak.

    Like you, I consider the Mak to be both an elegant and a fine instrument. So, as the old saying goes, where’s the beef? Why do you think this bias, this “deliberate scaremongering”, as you put it, exists? Where is it coming from? Why does it persist even after people like me, as well as legions of other happy Mak users, correct the naysayers over and over again?

    – Jon

    • Hello Jon,

      Many thanks for your message. You have a very nice website!

      Today, we as amateurs can enjoy a nice variety of telescopes to suit everyone’s budget and inclinations. Catadioptrics are fine telescopes, easy to carry about and mount in small and mid-sized apertures and a dedicated observer would just get on with enjoying the night sky. The largest Mak I have owned was a 180mm Orion and it was an excellent performer on all objects. The small field of view didn’t really bother me that much, as, like you say, the vast majority of deep sky objects can fit into its field.
      In regard to thermal issues, I never experienced anything significant, even in the large 180mm model, as all one has to do is a little pre-planning and in my situation I was able to store it for a few hours in a cool and dry outhouse, near the outside temperature and that always solved the problem for me. So I have no real sympathy for those who claim their Cats take too long to acclimate.
      The ‘scaremongering’ came from a small subset of the amateur community who tried to use the ‘thermal issues’ as a means to justify the purchasing of expensive apo refractors and my goal was to debunk this as an out and out lie.
      While many amateurs appear to revere these instruments, I take a different view, especially when the aperture is scaled up. The introduction of the apochromat was a solution waiting for a problem. It is not clever or innovative and has not been endorsed by the professional astronomical community. Other designs, such as the Newtonian, are far more effective and economical as the aperture increases. Neither did it occur to them that large triplet refractors, with their massive glass elements, cool off at a slower rate than a primary mirror of equal aperture. What is more, the Newtonian is truly apochromatic; the apochromat only approaches this, and at what cost?
      Seen in this light, I consider the whole ‘movement’ to be a nonsense.

      With best wishes,

      Neil.

  10. Hi Neil

    I’m the gentleman you refer to re the 5 inch f-15 and 715 intes comparison but of more pressing interest I now own a skywatcher 180 and have just confirmed the primary is 193mm possibly a recent change.

    I didn’t keep the 715 for long and recently tried unsuccessfully to buy it back but can’t complain now as the skywatcher is truly a fine instrument. I also recently scored a superb 10 inch f-10 intes micro Mak second hand what a monster but that’s another story.

    Greatings from Hokitika New Zealand

  11. Hello Phil,

    Greetings from a very sunny Caledonia.

    Good to hear from you and thank you for your message.

    That is very good news regarding the Synta 180 Mak.

    It was a most impressive telescope and I enjoyed my time with it, but I now get by with my Skywatcher 8″ f/6 Newtonian, which outperformed the former on all targets and cost far less. Such are the pleasant surprises of life!

    I will amend the essay so as not to cause any confusion.

    Best wishes,

    Neil.

  12. Dear Neil,

    Thank you for the very relevant insights you provide through your website.

    I’ve found your comment very useful about the Maksutov as I consider another instrument and am not sure about the best choice to make.

    May I afford to ask you some questions about your experiences with your scopes and possible advice?

    I have an achromat TAL 4″ on a Vixen Porta II mount. I have to say that I’m very impressed with the quality of the image it gives. Very sharp with a very good and surprising color correction. Really a nice instrument but what is also important to me is the confort in observing. I like the simplicity of the Vixen Alt AZ mount but it’s still a bit annoying to observe with a long refractor to the zenith ; and with a 1.000 mm focal length, it’s not easy to use the motion flexible handles while looking through the eyepiece.

    I’ve tried a 6″ F5 Newton on the Porta. Confort was really excellent. Steadiness was pretty good also. But visual experience was not satisfying for me. I immediately missed the sharpness of the TAL and found the coma too evident ; and I need more focal length to have a good planetary experience (as it’s what I observe the most).

    So I’m considering two options: a 150/180 Mak or a 6″ F8 Newton on my Porta II. But I wonder if the Porta can handle them. I assume the Porta will handle the Newton as it does with the TAL but I’m not sure with the Mak.

    I’ve seen on the picture published on your website that you’ve used the Mak 180 on your Vixen Porta II. What was your experience with this combination?

    I also found your reports about your Dobson F6 very interesting. I found this instrument quite appealing due to their large aperture and its 1200 mm focal length. I have nevertheless the idea it’s quite difficult to achieve good planetary observation due to the fact that there are not slow motion handles. May I also ask for your comment on this?

    Thank you very much.

    Best regards,

    Séba

    • Hi Seba,

      I forget to comment on the Vixen Porta II mount and its suitability for mounting the telescopes you have considered. I think the Porta II is ideally suited to small refractors in the 60-100mm catgeory, small reflectors like the 130mm f/5 I have showcased, and a number of small catadioptric telescopes, like the C90, C5/6 and Maks up to about 127mm. I think it would tax a 150mm instrument though and anything larger. I would be inclined to use a heavier mount for the latter, such as the SkyTee II altazimuth mount or a driven equatorial mount.

      Hope that helps.

  13. Hello Seba,

    Thank you for your message.

    I really want to draw a line under all this stuff. I’m tired of it and wish to move on. The problem we have is ‘choice’, which is normally a good thing, but too much of anything can be frustrating because it keeps us from just getting on with things. Today we are blessed with so many good inexpensive telescopes and you can do well with most any telescope design.
    In my walk, I have learned that the best all-round telescope is a 8-inch f/6 Newtonian. If I only had to have one telescope, that is the telescope I would choose.
    Failing that, a 6″ f/8 Newtonian would a good choice but it won’t satisfy like an 8-inch can.

    Enjoy whatever you have.

    Best wishes,

    Neil.

  14. Hello Neil,

    I can’t get enough of discussions about telescopes and about the subjective strengths of different designs…ahem..

    I pretty much concur that a well collimated, clean 8″ newtonian is the most cost effective solution for planetary observing and tbh a 6″ f8, 8″ f6 and 10″ f4.8 were my first 3 telescopes. The 10″ in particular surprised me with the detail I could see on the Moon, Saturn and even Jupiter. on some nights. The coma was very noticeable in the latter though. After going through the phase of aesthetically pleasing point stars without cma in small refractors and the maksutov-newtonians (which have great smooth optics) I realise that aspheric (parabolic) newtonians have now got pretty consistent in quality now and you can pay to have a specialist manufacturer made mirror from the US or UK of “guaranteed” quality if you want a better than 1/6th wave spec, but you have to wait for outstanding seeing to see any difference.
    Well sorry if I’ve drawn under the line here…

  15. Hi Neil,
    I have really enjoyed your voyage over the past years through various types of scopes. With todays excellent affordable reflectors, would you go as far as to say that refractors, no matter the build and glass origin, are obsolete?
    As I lately bought a couple of more expensive EP´s, my 10″ DOB really got new live – so this could almost be my conclusion..

    BR,
    Anders

    • Hi Anders,

      Thank you for your message. It is always a pleasure to share my telescopic adventures with others.
      To your question; I can really only speak for myself. They are not completely obsolete in my life. I own and very much enjoy a nice little 80mm f/5 achromat, which is great for looking round the landscape and observing nature. But for astronomical viewing at night, my larger reflectors are far more rewarding to use. My 8-inch f/6, in particular, is my most used instrument. I was out the other night, enjoying the return of dark skies after a hiatus of a few months. I ran it through the Milky Way in Cygnus using my 40mm wide angle eyepiece delivering 30x and a 2.3 degree field, and was totally blown away with the enormous number of stars it pulled in! The Universe is so very vast and beautiful! Your 10-inch should do even better. We are very fortunate to have such telescopes available to us today.
      I’ll be starting up a new blog on the northern Caldwell Objects using my 8-inch after I return from vacation.
      Enjoy your new eyepieces!

      All the best,

      Neil.

  16. Neil,

    Enjoyed your piece on the Maksutov telescopes. I have been quite successful doing planetary imaging with the Orion/Synta 180mm Mak. I would be pleased to send you a single image featuring Saturn, Jupiter, and Mars from apparitions for this season. To do so, I would need your email address. You can use the image any way you wish as long as the source is attributed.

    Best Regards,

    Ralph

  17. Good evening Ralph,

    Thank you very much for your message. I’m delighted you have had success with your Orion/Synta 180 Mak, which I have visually found to be a fine, high-performance and ultra portable telescope. You can reach me at neilenglish40@gmail.com

    With best wishes,

    Neil.

  18. Hi Neil, it’s nice to see you’re still posting here. Just dropped in to say hello. Your article came up in CN recently. Got a kick out of it being used as a reference. Cheers, mate.

  19. Hello Norme,

    Delighted as ever to hear from you again. It seems like an eternity since I last battled my way through the forums of CN, especially with little Iblis nibbling at my heels lol. Thanks for the thumbs up.

    I hope you are still enjoying your wonderful 150mm Mak; it sure was a great adventure debunking a telescopic myth such as this. You continue to be a great ambassador for the hobby and your work is still inspiring folk to get out under starry skies and explore its many treasures.

    All the best,

    Neil.

  20. Hi again Neil and all,

    There was a comment wondering whether refractors are all but obsolete.
    Well not exactly- for a start the various “superWASP” arrays use very fast f1.8 and f2.8 big camera lenses. Yes very expensive but the reason pros use the refractor still occasionally is that they can provide the widest, flattest, fully illuminated fields for astrophotography.
    In smaller apertures, the secondary mirror in a fast newtonian astrograph has to be big to fully illuminate a large camera sensor. This is another reason to reinforce the idea that refracting scopes for larger apertures is not usual.
    I still think that the synta 190mm maksutov-newtonian is under recognised though. It is that sort of all-rounder hybrid with far less coma than a regular (but much cheaper) 8″ newtonian, has a sealed tube and almost “apo-like” optics. I’ve seen the go for half price second hand, bafflingly (oh they are well-baffled too).

    I am enjoying the return of dark(ish for me) skies too….

  21. Having said that, an 8″ triplet apo is 30x the cost of MN190 and about 120x the cost of 200p. Haha.

    • Hi Alex,

      I’m sure you could be blissfully happy with your MN 190. I’ve not had the pleasure of using one, but I’d bet the images they serve up are very fine indeed. My 8-inch Dob ticks all the boxes for me though. I’m happy.

      Best,

      Neil.

  22. Hello Anders,

    I promised I would start a blog on observing the northern Caldwell Objects, but alas I don’t think I can do it for the foreseeable future, what with the amount of other work I have to press on with. I apologise for any inconvenience caused.

    Best wishes,

    Neil.

  23. Thanks Neil.
    I could be blissfully happy with an MN190 from skywatcher. I’ve not looked through one either but I’m certain it’d be almost as good as my intes-micro MN200 which is a had longer at f6 like your newtonian. The only real advantages maksutov-newtonians have over newtonians is the much reduced coma and sealed tube.

    However as you know coma is much reduced in newtonians when as the f ratio goes up. I still miss my old 6 inch f8 dobsonian in that I never noticed any coma with any of my 1.25″ eyepieces with it.
    In fact similar to refractors as you have said, aberrations rise markedly as f ratio is reduced from say f8 to f6. Spherochromatism in ANY refractor and coma in ANY newtonian goes up noticeably. You can see this if you go to your link here http://www.telescope-optics.net which is an inccredibly comprehensive site for ALL scope types. Seems to me that the simple long focus newtonian has fallen so out of favour compared with the apo refractors, fast astrographs and SCTs. This is probably because of convenience.
    This is despite the fact that a long newtonian is also is least expensive scope for any given aperture, especially and markedly as the aperture goes up. Over 6 in (150mm) I’d get a long f6 plus newtonian every time. The mak-newt’s lack of coma is the icing on the (heavy) cake though. A very good all-purpose type of scope indeed with fine theoretical and practical performance. This diminishes as aperture goes up though and the MN190 is a maximum for amateurs really.
    In fact the dream scope for large apertures of 12″ and over is basically a longish newtonian – from a purely visual point at least!

  24. (To clarify I meant that for apertures of 150mm or over, I’d go for a newtonian every time if budget was a factor, but would also consider it even if budget was not)

  25. Hello Alex,

    I entirely agree that bringing back slower f ratio Newtonians would be a good thing. They are by far the simplest and best design to scale up. A 8,9 or 10-inch f/7 would be great options. They would be so easy to collimate and keep accurately aligned that they would be as maintenance free as a refractor. Folk clearly shop for convenience these days and can’t seem to tolerate even occasional adjustment, so this move would be welcomed I think.

    What about something like this?

    http://www.cave-astrola.com/resources/Losmandycavecatalogsm.pdf

    Best wishes,

    Neil.

  26. Hi Neil,

    That looks a bit like my UK made 10″ f6.3 that I got several years ago.
    I have seen a few lunar images taken with cave astrolas from a couple of older amateurs and they seem to have fine optics. I’d not heard of them before that. My first dobsonian had a Davids hinds 6.25″ f8 mirror. Was state of the art to me in 2003!
    It’s collimation never needed adjustment.

  27. I am Satish Patil from Jalgaon Maharashtra State India.Dear Astronomer I had lot of doubts about Max tele specially its short fild of view and low brightness.I had 4 inch max. but I sold it. But now I am thinking that it was my mistake.without using it and testing it properly I sold it But now I get new vision.Soon i will buy max. Thanks a lot.

  28. Hello Satish,

    Maks are nice telescopes. Enjoy it when it comes.

    Season’s Greetings,

    Neil.

  29. 3 years on and this topic is a fresh as it was ; thank you !

    Maks such as the OMC are an interesting design ; unfortunately it seems they are not easy to remote-control the focus !

  30. Hi Neil and all,

    There is still one special thing that maksutov-cassegrains and refractors have over newtonians then, apart from the low coma and protected mirror:
    That is the ability give correct oriented images to the eye for daytime terrestrial viewing. Whether high power or low power, this is why the market for the “spotting scope” is so big. The market for the humble binocular is even bigger, look how many of these have been sold. I think just about everybody has or has had a pair!
    Relatively few have ever simply pointed their binoculars at the night sky though.
    Heck if Galileo hadn’t been about even fewer might have.

    I keep my “eye(s) peeled for a nice big pair of binoculars of 5 inches or greater, preferably with angled, interchangeable eyepieces, of around the cost of a mid-size telescope….

  31. Hello Alex,

    Small Maks and refractors are fine spotting ‘scopes and are deservedly popular. I have a nifty little ST 80, which I use regularly and, of course, the venerable C90 is great value for money too.
    These days we really are blessed with so much cool stuff.

    Best wishes,

    Neil.

  32. Yup. I just got a 2nd hand meade ETX105 which has almost perfect optics. Symmetrical intra and extra focus patterns even. Certainly have it many times better than last generation of amateurs. Tonight here and before dawn this morning, the seeing was exemplary. Stars show nice little airy discs. The Moon was amazing at 300x. Jupiter showed white patches and at 06.13am a Jovian moon emerged from the Jovian limb like a white pimple. (Seen with big mak, not etx)

  33. So it’s personal choice at the end of the day in your quest for the most perfect telescope for you. Both maks and newtonians “do what it says on the tin” and better, whether chinese or other optics. Whether newtonian, mak-newtonian, mak-cassegrain or refractor.
    Me, think having a nifty 80mm apo ‘fractor as all-round portable scope, compact mak-cass for quick lunar/planetary/double star scope and large newtonian for deep-sky and planetary for the nights of best seeing is the most cost-effective, practical combo. Maybe substitute that apo for an achro if on a budget.

    Clear skies.

  34. Morning Alex,

    That’s what it’s all about really. An 80mm refractor is very useful alright but I also like my 130mm f/5 Newt for quick grab ‘n’ go. Seeing was iffy this morning and the altitude of Jupiter wasn’t that inspiring but I managed a fairly decent view at 122x using the Televue Bandmate Planetary filter as it crossed the meridian. Lots of activity in the NEB I see. Hoping for steadier air sometime.

    Cheers,

    Neil.

  35. Hi Neil,
    A very interesting discussion.
    I use a Skywatcher 180Mak for visual double star measures. The telescope is permanently pier mounted in a run-off observatory, and is completely dedicated to this activity. In conjunction with a Meade 12mm reticule, a nominally x2 Barlow generates a focal ratio of 31.4 and a working power of x477. This results in a division constant of just 3.69″. At this scale close binaries become viable targets. The closest pair yet measured is Zeta Cnc AB at 1.09″, giving a residual of only 0.03″ from the published orbit.
    An account of the calibration process for this system, as well as a set of measures, will be published in the 2018 issue of the Webb Society Double Star Section Circular. (It would have happened this year if the weather had been kinder!).
    The Maksutov was chosen quite deliberately for this work (largely on the advice of Denis Buczynski). It has not disappointed. In the past I once had regular use of a 6 1/2″ Cooke refractor and I can say categorically that to my eyes the Maksutov delivers images every bit as good – and without the colour!
    All the best, Rob

  36. Hello Rob,

    Many thanks for your message.

    Thankyou for your testimony and for taking the time to make these tests; I appreciate it very much.
    I formed the same conclusion when I tested my beautiful, handmade, 5″ f/12 refractor against the 180 Orion Mak. It is not a venerable Cooke refractor, of course, but apart from a smaller maximum true field, the Mak was superior on pretty much everything. The whole experience proved trenchant for me.

    I wish you many nights of observing happiness with both your telescopes.

    Best wishes,

    Neil.

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