Questar 7" Classic Titanium Maksutov-Cassegrain, broadband coatings, Zerodur mirror

$13,295.00

Availability: More on the way

Is this Questar Seven Classic Titanium the ultimate mid-sized telescope? I think so. I own a 7" Classic with broadband coatings and a Zerodur mirror and I can't think of another scope I'd trade it for . . .
Our Product #: Q7CBZT
Questar Product #: 20302
 

Product Description

Look through a Questar Seven Classic Titanium optical tube with broadband optical coatings and a Zerodur mirror, and you're looking through the ultimate mid-sized telescope. You'll see detail and clarity in the skies that you have never seen through any lesser scope, or even through many larger scopes. I have compared my own Questar Seven to a 14" Schmidt-Cassegrain on deep space objects such as the Sombrero galaxy, the Saturn Nebula, and Omega Centauri. While the 14" scope was brighter on the fainter objects, the superior contrast and resolution of the Questar Seven was easily visible . . . even to the owner of the 14" scope. The Crêpe Ring and Encke's Division in the rings of Saturn are routine with a Seven Classic in good seeing, as are myriad whorls and festoons in Jupiter's belts and hundreds of sub-kilometer craters on the lunar surface.

What is it about a Questar that lets it outperform larger scopes on a day in/day out basis?

Simply this: a fanatical devotion to hand-crafted accuracy.

Each optical element in a Questar typically tests out at a truly outstanding 1/50th wave accuracy (shaped to within four ten-millionths of an inch of perfection!) This produces guaranteed total system performance at the Cassegrain focus of 1/8th wave or better. That's twice the accuracy needed to meet Lord Rayleigh's Criterion, which specifies the level of optical excellence required to yield visual performance that is indistinguishable from perfect optics.

Most commercial telescopes claim to be "diffraction-limited" (which is generally assumed to mean 1/4th wave accuracy). However, they do not specify whether that is for individual components or the system as a whole. In either case, it's a far cry from the 1/8th wave total system accuracy entering the eyepiece of a Questar.

This significant difference in total system accuracy is one reason why a 7" Questar can routinely outresolve a 14" Schmidt-Cassegrain (or virtually any other larger aperture catadioptric or reflector scope) on globular clusters, binary stars, and lunar and planetary details - with the Questar invariably exceeding Dawes' limit for the best resolution available from an optical system of its aperture.

A second reason is the turbulent Earth atmosphere all telescopes must look through. In essence, when observing, you are usually looking through bubbles of disturbed air - microcells typically 4" in diameter in the layer of the atmosphere nearest the surface of the Earth. The larger the aperture of the scope, the greater the image-blurring effect of these microcells, as the larger scopes simply have to look through more of these turbulent cells than a smaller scope.

Finally, there is the matter of contrast. The small secondary mirror of a Questar Seven Maksutov (only 1.87" in diameter) scatters far less light than a 14" Schmidt-Cassegrain's much larger 4.5" secondary. The same holds true with any other larger reflector or catadioptric telescope you care to name. They all have larger light-scattering secondary or diagonal mirror obstructions than a 7" Questar Classic Titanium. In addition, a Questar's central baffle tube is not merely black plastic or painted black to reduce reflections, as with lesser scopes, but is a centerless ground stainless steel tube, anodized matte black and containing a wire helix with 19 internal knife-edge baffles to eliminate low-angle reflections that no paint alone can stop. The result is that a Questar scatters less light from the bright areas of an image into the dark - crisply defining high contrast planetary and lunar details that a larger scope can wash out in a haze of scattered light.

A large aperture scope does have greater light-gathering than a 7" Questar to capture additional faint deep space objects from a dark sky site. However, the higher contrast of a Questar lets the multitude of galaxies and nebulas within its grasp stand out more distinctly against a darker sky background, particularly from light-polluted suburban or city sites where a larger scope's greater light-gathering capacity submerges subtle low-contrast deep space details in a fog of city light.

As a Rolls-Royce is to automobiles, so is a Questar to telescopes - the very finest hand-crafted optical performance that money can buy.

The Questar Classic Titanium is precision-fabricated of specially lightened aluminum and titanium, with a black and blue anodized finish for long life. Questar engaged in an extensive heat transfer analysis to refine the shaping and milling of the internal components to dissipate heat and rapidly bring the optics down to ambient temperature quickly. This was done to avoid having to resort to the use of powered fans to cool the optics as others do (which can suck image-degrading dust into the optical path).

All internal components (such as the main tube mounting plate, mirror thimble, and central light baffle tube) are titanium, with milled surfaces to increase heat transfer and lighten weight. The optical tube is extruded and stress-relieved aluminum. The control box is machined cast aluminum, with milled internal surfaces to increase heat transfer and lighten weight. It is externally painted with special aluminum paint and clear overcoated for durability. The interior is finished in anti-reflective matte black paint.

The control knobs on the rear cell are turret lathe-turned anodized aluminum, with sharts and control levers of stainless steel. The focus knob focuses the scope by turning a spring-loaded 1/4"-32 thread stainless steel focus rod that acts directly on the titanium mirror thimble to move the primary mirror along the titanium central baffle tube within the optical tube. A precision linear ball-type bearing, integrated with the mirror mounting, is matched to central tube thimble to minimize mirror shift when focusing.

The optical tube barrel of the Questar Seven Classic Titanium is wrapped with an accurate full-color silk-screened star chart. The thread-on dewcap is wrapped with a useful silk-screened map of the Moon.

The Seven Classic Titanium uses a 7" diameter meniscus corrector lens of Grade A BK7 optical glass, with magnesium fluoride anti-reflection coatings for high light transmission and minimal reflected light loss. The 7.6" diameter primary mirror is Pyrex, aluminized, with a silicon monoxide (quartz) overcoating for long life.

Insert the Questar's premium 24mm 1.25" Questar Brandon eyepiece into the eyepiece holder on the top of the control box at the rear of the scope. Look in and you're looking into a 7.6x finder with a wide 7° field. A finger touch on a convenient lever at the rear of the scope changes the finder into a 106x telescope for observing the Moon, nebulas, galaxies, and star clusters. Touch a second lever and a built-in 2x Dakin Barlow instantly increases that eyepiece power to 212x for closer observing. Exchange the 24mm eyepiece for the supplied 16mm 1.25" Questar Brandon eyepiece and you extend the power range still further, to an 11.5x finder with a 4.6° field and a 159x and 318x telescope. You never have to worry about the telescope and finderscope getting out of alignment with each other, because the finderscope in an integral part of the telescope body itself. Optional higher and lower power 1.25" Questar Brandon eyepieces are available, for magnifications as low as 63.5x and as high as 635x.

In addition, the Questar Classic Titanium can be equipped with an optional 2" mirror star diagonal that threads onto the rear cell. This lets you use longer focal length 2" Brandon and third party eyepieces to lower the magnification to as little as 45x.

The Questar Classic Titanium weighs 19 pounds, 21 pounds if you add the thread-on dew shield). It measures 22.6" long. The low profile mounting adapter block on the underside of the Classic Titanium has both 1/4"-20 and 3/8"-16 mounting holes to allow to be installed on the Questar Equatorial Fork Mount (our part #20004) and Questar Large Classic Titanium Pier (our part #29338) for astronomical use. It is well-balanced and relatively light, allowing it to be mounted on any suitably sturdy tripod for terrestrial operation. It can also be adapted to your own equatorial mount with minimal effort.

This Questar Seven Classic Titanium has a broadband dielectric multicoatings package that includes ultra-high transmission/low reflectivity broadband dielectric multicoatings on both sides of its objective lens for a light loss of less than 1/10th of 1% per surface for the brightest possible images. This compares with a light loss of 1% per surface with standard magnesium fluoride antireflection coatings. This multicoatings package also includes high reflectivity silver mirror coatings with a protective overcoating of thorium fluoride instead of standard aluminum coatings with a silicon monoxide overcoat. The broadband coatings package gives you a full 22% overall gain in light transmission and contrast that's very useful for photography and when viewing faint deep space objects.

This broadband coatings package is not recommended if you live full time on ocean-front property, or spend much of the year at the seaside. Constant exposure to salt air can adversely affect the silver mirror coatings. Occasional visits to the shore are not a problem, only extended stays (particularly if the scope is not packed away in its case when not in use). Adding a few packets of desiccant (silica gel or similar, available at most camera stores) to the case to absorb moisture when near large bodies of salt water would be a helpful preventative measure in any event.

This Questar Seven Classic's thermally stable Zerodur ceramic mirror eliminates the need to refocus the scope as it cools to ambient temperature in situations involving large temperature swings. As with any Pyrex mirror telescope, if the difference in temperature between indoors and outdoors is 30 degrees or more when a Questar is taken outside, some refocusing will be required as its mirror contracts while cooling down to the outdoor air temperature. This is particularly true with a relatively large aperture scope like this Seven Astro, which has an oversize 7.6" primary mirror. Some people find the need for even an occasional refocusing to be annoying. Since a Zerodur mirror exhibits virtually no expansion or contraction as temperatures change, this option eliminates this need for refocusing. This option is well worth considering due to the large thermal mass of the 7" mirror and its consequently longer cool-down time than a smaller scope. I have both broadband coatings and a Zerodur mirror on my Questar Seven and can recommend them without reservation.

The Questar Seven Classic Titanium comes in a high impact ABS plastic sealed carrying case with wheels and transport handle. A basic 35mm camera coupling set is also included (needs a Questar T-ring to connect to your camera).

This Questar is protected by a ten-year Questar warranty (two-year warranty on the focuser mechanism and five years on the broadband coatings).

Absolutely pinpoint resolution, total freedom from spurious color and distortion, with an image clarity and contrast in a class all its own - a Questar is truly the Rolls-Royce of telescopes. For those individuals who appreciate the very finest that life has to offer, a Questar Seven Classic Titanium with broadband optical coatings and a Zerodur mirror will prove to be an absolutely eye-opening astronomical revelation. It is indeed - in performance and built-in features - the ultimate mid-sized telescope.

Tech Details

Aperture 7"
Binary and Star Cluster Observation Very Good
Focal Length 2425mm
Focal Ratio f/13.6
Galaxy and Nebula Observation Good
Heaviest Single Component 19 lbs.
Highest Useful Magnification 423x
Lunar Observation Great
Weight 19 lbs.
Planetary Observation Good
Resolution 0.65 arc seconds
Visual Limiting Magnitude 13.8
Warranty 10 years

Reviews

Review by:
This OTA with the control box is one of the best and easiest to use long focal length telescopes I own. Without the Questar fork arms and with an adapter plate underneath for a Losmandy or Vixen style mount this is 7" of aperture that is VERY easy to get on and off a GEM and gives amazingly sharp views, especially on lunar, planetary, and double star objects. With a bino viewer this scope gave the best views ever seen by our astro club members of Saturn, as the contrast was nothing short of astounding. For visual use, longer FL this is the scope I want to use. I WOULD caution that it is not my favorite for astrophotography, as ALL Mak-Cass optics suffer spurious light rings from nearby bright stars out of the FOV. My favorite way to view is with a 2" diagonal through the photo-axial port off the back so I can use ANY eyepiece I'd like, and still have the finder view in play through the native eyepiece on top of the control box. You need a VERY large aperture apo to compete with a Questar 7, and I for one prefer the shorter tube length and easier setup of the Questar. For that reason this scope gets used - OFTEN! (Posted on 10/6/2018)
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