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The Questar 3.5 Standard

Posted by Malcolm Bird   03/01/2010 08:00AM

The Questar 3.5 Standard
Questar 3.5” Standard

Who amongst us has not lusted after a Questar? Ever since most of us have been in the hobby, we have been tempted by reports of these perfect little jewels. You all want one, come on – admit it. But do they live up to the hype? I no longer have my Q, but thought I would post my thoughts and experiences on this scope so people would have a counterpoint to the effusive ads from the NA Questar retailer.

I succumbed a while ago when I saw a Questar 3.5” Standard for sale on a Canadian astro buy sell site, and I could drive to meet him and eliminate the nail biting on the shipping end of things. So I took the plunge, literally sold off almost every bit of my astro gear, and found myself the proud owner of a Questar 3.5 Standard. For those not familiar with the Questar offering, the 3.5” comes in 3 flavors, the ‘Standard’ astro model, the ‘Duplex’ model which allows the OTA to be dismounted from the fork mount for use as a spotter, and a dedicated Field spotter OTA for mounting on tripods via standard ¼-20 threads ala camera mounting.

My particular version was a ‘Standard’ made in 1978 and had the broadband coatings option, as evidenced by the ‘BB’ in the serial number etched in the base. This is Questar’s version of Starbright or UHTC coatings. The mirror substrate was the standard Pyrex. It is also available in Cervit and Quartz.

First impressions

On meeting the seller (finally, in a cold, windswept parking lot because neither of us thought to give the other our phone number and only happened to recognize each other because of the mutual franticness with which we were scrutinizing every car for potential matches – him for his money, me for my new toy…lol), he opened the trunk of his car and there it was – the Questar leather carrying case with a complete (if the ads are to be believed) observatory inside. I’m ashamed to say my first thought was ‘why was the scope in the trunk while the guy’s wife was comfortably ensconced in the passenger seat?’ I mean, shouldn’t it be the other way around…..!

All heresy aside though, he opened the case and gingerly lifted the Q from its nestled resting place and handed it to me like a newborn. My first impression was that it was indeed jewel like. It had the signature deep purple sliding dew shield with the star map silk-screened on it and it was a beautiful contrast to the bright polished and lacquered aluminum of the fork mount and base. It looked new.

The second impression was how small it was. I know it is only 3.5”, but somehow, I expected it to be larger. Overall, it’s about the same size as an ETX90 for comparison. It should be, as the ETX90 was basically patterned after the Q3.5”.

So after a careful look at and thru the optics (clean and bright), a quick twiddle of all the controls (smooth and precise) and a quick inventory of the parts and accessories (all there as advertised), my wallet was a lot lighter, and my driving on the way home way more careful than if I had mere human passengers in the car with me…

Once I got home, I served notice to all those around me that I had some serious evaluative work to do, and that I did not want to be disturbed. Of course, my wife by now was used to this and correctly interpreted it as ‘I want to play with my new toy alone’. As is usually the case, horrible weather accompanied the new telescope, so I had to satisfy myself with views in and from within the house.

The basic scope

The Questar 3.5” is a classical Maksutov design with the deeply curved corrector with the aluminized ‘spot’ on the inner face that serves as the secondary mirror. The optics are made by an optical company called Cumberland who apparently also makes optics for the US military. Not bad credentials. The Q3.5 operates at a nominal F14.4 giving it a focal length of 1300mm. This is housed in an OTA that is about 11” long.

The OTA is mounted on a traditional dual fork mount made of polished aluminum castings. The base is a round, flanged affair, again of highly polished aluminum. There are setting circles, and slo motion controls on both axis (more on this later) and the RA/AZ axis is motorized with a 110Vac synchronous motor. The whole scope weighs less than 7lbs.

The rear cell houses a built in diagonal mirror and the eyepiece holder accepts either screw in style Brandon or standard 1-1/4” eyepieces. Early Q’s were setup for just the screw in style Brandons, but adapters are available for the older Questars to give them this same functionality.

So what makes it different?

So far, other than the use of aluminum, I could be describing the ETX90. But generalities are all they share. There is no comparison when it comes to the use of materials, the fit and finish, the designed in functionality and the attention to detail.

Despite all the above, there are two other areas where the Q3.5 sets itself apart.

The first is the one the Questar is famous for. It is the OTA rear cell, which Questar calls the ‘control box’. This control box houses a variety of levers and mechanisms which allows you to do the following:

1. flip between finder mode and main scope view.
2. Flip a Barlow lens in and out of the optical path thus doubling the power.
3. Flip a solar filter in front of the finder lens.
4. Focus the main optics
5. rear cell aperture for axial mounting of camera equipment.
6. diopter adjustment for finder scope.

We have all fumbled about in the dark for that Barlow or desired EP focal length. We have all craned our necks and backs (to our chiropractor’s delight) in order to site through inconveniently located finder scopes. Well, the Q’s control box allows you to select finder view (4X), main scope view (54X) or barlowed main scope view (100X) without having to move your eye from the eyepiece. The only thing you have to fumble for is the 2nd Brandon 16mm EP which then gives you 8X, 81X and 160X. These numbers are approximate as Questars shipped with internal barlows that varied between 1.8X and 2X over the years.

The Barlow is not parfocal, and minor refocusing is required when toggling back and forth between powers. The finder will not come to focus with the Barlow in.

It is very satisfying to accomplish all of this with a casual flick of a lever. It is hard to describe how beguiling these functions can be.

The second area is in optical quality. Like a high end APO, you know you are getting unquestionable optical quality. We have all had telescopes where we have secretly been wondering if the seeing was always bad, or maybe the optics on my scope aren’t quite what they should be….

Typical Questars provide 1/6-1/8W at the eyepiece. (their anniversary edition guaranteed 1/10W) This translates into crisp views, an unambiguous focus point, and a small aperture scope that you can push to stupid levels of magnification before the image starts breaking down. If the images aren’t good – it’s not the scope.

What’s in the case?

My Questar came housed in a leather (vinyl is standard) case with combination locks and measured approx. 10 x 10 x 16”. The Q3.5 slides neatly into the velour lined interior which also has pockets and recesses for the following standard accessories.

• 2 eyepieces. 24mm in a pocket on the door, 16mm in the scope
• A sub-aperture solar filter
• A close focus stop diaphragm
• Equatorial table top mode legs (3)
• Power cord for the RA drive
• There is a pocket for the PowerGuide II 9v battery conversion if your scope has it, and a bit more room for a couple of other small accessories.

The complete kit weighs in at about 12lbs. It truly is an observatory in a box, with limitations mind you, but still quite an accomplishment.

Main Optical performance

One of the Questar’s claims to fame is faultless optical performance. Judging by my Q, this reputation is born out. In the early days before the weather cleared up I had to satisfy myself with thru window views. Even then, the Q3.5 put up images that belied the fact you were looking through 4 layers of float glass. The OTA is well baffled and use in the daylight does not create any flaring or washouts as it does with my ETX spotter. The dew shield can slide forward to provide an effective light shroud. It is lined with flat black felt.

Views down a long hallway (we astronomers are a desperate lot aren’t we..) to a Christmas wreath hanging at the end took magnifications up to 320X and were still clean. That’s almost 100X per inch of aperture!

The skies cleared a few days later and gave me my first celestial light. Star images were textbook perfect showing perfectly round stars with 1 clearly defined diffraction ring. The focus was right ‘there’. No guessing - no mush either side - you just knew that you had it. The moon images were color free and with high contrast and you could push the magnification to silly levels. Views of Jupiter were bright, crisp with obvious colors in the banding. The moons were pinpoint stars around the disc. The feel of the focuser was very smooth.

The only caveat to all this gushing, is that no matter how perfectly figured the optics, or efficient the coatings, the Q3.5 is still only a 90mm scope with all the limits in light grasp and resolution that the laws of physics impose. However, within these limits, the optics are effectively perfect.

As previously mentioned, the rear control box makes changing of power a breeze, but the finder system deserves some discussion as it is unique in the telescope world.

The finder System

The Q3.5 finder consists of a square diagonal mirror slung below the scope that bounces light from under the OTA up to a 16mm achromatic lens housed in the control box. A glass solar filter can be switched in to cover the finder mirror at the flick of another lever, so with the included main objective solar filter, you have a solar observatory with a solar compatible finder.

The finder objective is approximately 100mm focal length, so that when the diagonal mirror is switched out of the way via one of the control box levers, the finder light cone can proceed up to the eyepiece. The finder power therefore depends on what EP is in the holder at that point. (hence the diopter adjustment on the holder) When the lever is flipped back, the finder optical path is blocked and the main optical path is diverted to the EP. Both Bandon EPs worked with the finder, however, my other EPs required more ‘in’ or ‘out’ focus than the diopter adjustment could provide.

With the 24mm EP, the finder provides a very wide (12*) and sharp field of view. Unfortunately, 16mm does not provide much light to work with. The finder is fine for locating bright objects or for daytime use, but don’t expect to find any Messier objects in it. This makes locating celestial targets a sometimes frustrating experience. Don’t forget, the main scope is working at F14.4 which gives it an excruciatingly small field of view. Without a finder to pinpoint the target, simply sighting along the barrel won’t work, so the Q3.5 falls down in this regard.

The eyepieces

The Q3.5 ships with 2 Brandon eyepieces – usually a 24mm and a 16mm. Questar opted to go with the Brandons because they wanted to keep the whole telescope ‘Made in USA’. My hat is off to them for that!

They also chose the Brandons because they have excellent color correction, sharpness across their 45*FOV and are very light. In comparison tests, I found the Brandons to provide slightly brighter and contrasty images than my generic Plossl’s with a slightly cooler color tint. They are a very good match to the Questar optics. I kept trying my other Plossls and SWA EPs but in the end, kept coming back to the Brandons. I found that with the 24 and 16mm Brandons and built in Barlow, I didn’t really need other EPs – which was Questar’s intent all along.

The mount

The Q3.5 uses a traditional dual fork mount that can be used in ALT/AZ mode, or with the supplied legs screwed into the base, in equatorial mode. It is very compact and light.

To convert to equatorial mode, jut pop the two fixed length legs into the side holes and the adjustable leg into the center base hole and presto chango, you have a table top equatorial mounted telescope. Which sounds great until you have to use it. Got a sturdy table handy?

This is the one area where the ‘observatory in a box’ comes unhinged. You really need a sturdy tripod to mount the Q3.5 so you can get it up to a comfortable and useful eye height for astronomical use. Questar offers a gorgeous anodized aluminum tripod, and many owners use Lindhoff tripods. But in a pinch, it works, and in ALT/AZ mode for terrestrial use where the OTA is essentially horizontal, this is not a factor.

The Questar mount is unique in that it uses a form of roller friction drive on both axis. (it is only a matter of time before this statement is pointed out as false too, so I’ll anticipate that….the ¼ Hitch Mounts advertised elsewhere on this site also use a roller friction drive system.)This is accomplished by a small diameter grooved steel driver shaft bearing against a thin large diameter stainless steel disc. The benefits of this system are that it is positive and has no backlash. Both axis are essentially ‘clutched’ by this high pressure interface.

You can still shove the telescope around by hand but you have to overcome the friction of the steel on steel. You can also override the drive to make manual adjustments and it will just pick up where you leave it. I found the slo motion controls on my scope to be fairly stiff. They were smooth, and you could make adjustments without too much shake, but I felt they were unnecessarily stiff. Whether this is a function of the design, or whether my unit needed some TLC I can’t say. They certainly were not ‘buttery’ as the ads declare.

The other aspect of this drive system that I discovered one evening is that because the drives depend on friction, anything that decreases this friction, like dew for instance, can cause them to slip….

The 110Vac synchronous motor drive runs off household current (read extension cords) and it is quiet, smooth, positive…….and ancient. In this day of GOTO,or at the least, dual axis drives, the Questar remains stubbornly rooted in the 60’s where the only scopes that had drives were on Mount Palomar. I think it is a very telling fact that in virtually every post you see for Questars, the AC cord is still tightly wrapped from the factory – ie: probably not been used……

I found it a bit disappointing that such an elegant and well thought out optical tube should be let down by the mount.

Options are available from Questar and 3rd party suppliers that bring to some modern functionality to the Q3.5 – see addendum below.


Despite my crabbing, overall, the Q3.5 is an amazingly well thought-out telescope. That it has been around since the 50’s,largely unchanged is mute testimony to its sound design. Everything just ‘works’. It abounds in little details that endear it to the owner. From the sliding dew shield with the silk screened star map, which slides up to reveal a similar silk screened lunar map, to the screw on objective cover, to the fascinating functions of the control box to the unique drive system, it is a tinkerer’s delight.

If you like machinery, if you like finely machined whatevers, you will enjoy the Questar for what it represents and how it is accomplished. There is a undeniable presence to the Questar that you do not find in any other scope.

Sure, high end APO’s are elegant in their austere promise of perfect imagery and color correction, the GOTO scopes are impressive in their technical capability, and big dobs are, well,..big. But the Questar is fascinating and attractive. It looks good on a bookshelf, yet acquits itself well in use. You just want to touch and fiddle with it.

And if you think about it, a bare bones high end 90mm APO will cost you more than a perfect used Questar, and you won’t get a mount or accessories with it. And after you have antied up a lot more $$$ to mount that APO and accessorize it, you certainly won’t be able to carry it outside in one hand and be observing in 2 minutes flat.

And at the end of the day, you just have another 90mm APO….. but heh! – that guy over there’s got a Questar!

Who should buy a Questar?

You should consider a Questar if;

• You can afford it. Good used ones are $1800 and up. New ones are $5000…..
• You are not into deep space observing
• You love finely crafted instruments
• You have other telescopes for more light gathering applications.
• You want a high resolution daytime observing/imaging system.
• You want a highly portable, airline carry-on compliant telescope that can do double duty on terrestrial or astronomical use.

You should forget about a Questar if:

• It is the only scope you will be able to use.
• You have to sell all your other Astro gear to afford it (I shouldn’t have bought a
• You can’t live with only 90mm of aperture.
• You are a techno geek. The Questar is firmly rooted in the 60’s and will stay there. No upgrades are available that will change this. (this statement has been proven to be incorrect – see addendum below)
• You want wide field viewing.



Since the original review was posted, I has been pointed out to me that there exist several optional add-ons for the Questars that can bring them closer to the 21st century.

The aforementioned PowerGuide II allows 9V battery operation and fine speed adjustments of 1.4X and 10X sidereal. These speeds are useful only as fine guiding and centering speeds. As reference, the 10X speed would equate to the 3rd slowest speed out of 9 on a typical Celestron or Meade GOTO system.

Declination drive – Available from Questar. Requires PowerGuide II option. Comments as for Powerguide II

3rd party encoder kits for ‘push to’ capability.

Questar anodised aluminum tripod - like the Q itself, as much a work of art as a piece of functional equipment.

As the gentlemen that pointed out these accessories to me conceded – nothing is cheap for a Questar…..but as the old Ferrari joke goes ‘If you need to know what the gas mileage is – you probably can’t afford the car……’

Questar Pros

Perfect optics
Ergonomically without equal
Indeed a complete observatory in a box with caveats as mentioned.
Very light and portable.
Nothing else like it. (ETX’s don’t count – sorry Meade guys)

Questar Cons

Low tech mount. (can be upgraded by Questar and 3rd party add-ons)
Only 90mm aperture
No tripod included. Questar and aftermarket solutions exist.
Accessories are limited and expensive

In Closing

I don’t have my Q3.5 any more. I am an inveterate trader and user of telescopes. My wife says I don’t buy scopes - I just rent them. In the end, as much as I enjoyed the Questar, all of my discretionary slush funds (read: funds sequestered from wife) were tied up in this one little jewel of a telescope, and in the end, I wanted to try other things.

Would I buy another Questar? Yes, but only if I could afford to own the Q and not have it impact my other Astro activities. I might consider getting my hands on a Field version so I could adapt it to my GOTO mount and enjoy the best of both worlds.

But I’m glad I had a chance to see if all those ads were true, and you know, they weren’t far off!