Questar Field Model, 90mm, broadband coatings, Zerodur mirror, 53/80x, case

by Questar Print

What would you like to print?
(Reviews and Documents/Videos will not be printed)

Basic Product Information
Full Description
Tech Details
Supplied Accessories
Recommended Accessories

More product information
With all due respect to the other spotting scopes shown on this site, there can only be one “best spotting scope in the world.” This Questar Field Model with Broadband coatings and a Zerodur mirror is it. Its resolution is truly remarkable, exceeding the theoretical limits for a 3.5” aperture scope. While optical theory predicts 0.33” resolution at a distance of half a mile, a Questar can routinely resolve much thinner bicycle spokes at the same distance, and show you leaf stems at a distance of one mile!

One of our customers from Nebraska called up shortly after he received his Field Model to say his scope clearly showed the power line into his neighbor’s house. We didn’t think that was all that impressive – until he told us his neighbor lived three miles away! As a review in Audubon magazine noted, “Brighter than reality, the Questar has unbelievably sharp resolution and an extremely flat field. It shows every feather from a half-mile away!” (Exclamation point theirs.)

A Questar has no astigmatism or chromatic aberration – no optical problems of any kind – to detract from your enjoyment. The Audubon review added, “the Field Model is unrivalled as a catadioptric spotting scope. It sets the highest standards for both optical performance and convenience of use.”

A review in Cornell University’s Living Bird magazine said, “The legendary Questar. There’s no question that for the right application this is a fantastic scope.”

And just what is the right application? According to the Living Bird review, “there are times when the Questar is indispensable. During the World Series of Birding, the Lab team spied a white blob on an old water tower. Rick put his trusty Bushnell Spacemaster on it at 22x – still a white blob. Kevin tried the Kowa TSN-4 at 60x and saw a white blob that might be a large bird. Finally Todd trained the Questar on it, flipped to 80x, and got a crystal-clear image of a roosting barn owl.”

What is the right application? It is any birding challenge where you need absolutely razor-sharp views of distant birds. The supplied standard equipment eyepiece gives you a basic 53x magnification. A built-in Barlow lens increases that power to 80x at the touch of your finger on a lever at the rear of the scope. Another lever instantly converts the 53x eyepiece to a 4x finder with an exceptionally wide 12 degree field of view (630’ at 1000 yards). You never risk losing your subject as you move your eye from finder to eyepiece, because finder and eyepiece are one and the same. (Both provide erect but reversed mirror images.)

For those birders who prefer lower powers and a wider field for close-in birding, an optional 40x eyepiece is available that provides 60x when the built-in Barlow is used. With the optional 40x eyepiece in the eyepiece holder, the 4x finderscope magnification drops to 3x, but with an even wider field of view (14 degrees, which is a very wide 735’ at 1000 yards). The 40x eyepiece can be substituted for the standard equipment 53x eyepiece at no extra cost, if the substitution is requested at the time your scope is ordered. The 40x eyepiece is also available for separate sale, to give you a total of four separate magnifications from only two eyepieces (using the scope’s built-in Barlow lens to increase the power of each eyepiece). A rolldown rubber eyecup is provided on all eyepieces for eyeglass use, although eye relief is relatively limited at higher powers.

Because of its high power and its ability to focus as close as 8’ (although with a very shallow depth of field at that close a distance), the Field Model is a marvelous long distance microscope for close-up studies of subjects that are too small or too dangerous or too fragile to examine at close hand – ant hills, bee hives, spider webs, etc. At its standard 53x magnification, subjects 10 feet away appear the same size as they would if you could get your eye within a mere 2.2” of them, with a field only 1.8” wide filling your eyepiece! Imagine your views of gape-mouthed chicks being fed in nearby nests, hummers at feeders, and more!

The black and satin-finished aluminum Field Model comes with a 3/16” thick machined thread-on metal protective dust cap. A slide-on metal lens shade improves both visual and photographic contrast. Other standard equipment includes a camera coupling set that lets you use the Field Model as a razor-sharp 1400mm (28x) f/16 telephoto lens by adding an optional Questar brand P-thread T-ring to fit your particular camera body.

The Field Model has extremely precise 50-turn knob focusing. (We Questar owners soon learn to roll the side of our finger along the side of the focusing knob to speed up focus changes, rather than turn, turn, turn with our fingertips.) Faster-acting 24-turn focusing is available as a factory-installed option for more quickly tracking moving birds and wildlife (although at the cost of increasing the close focus distance to 25’ from the standard 8’).

An optional roof prism image erector, #6351, is available to allow straight-through viewing (from inside a car being used as a mobile blind, for example, using an optional car window mount). There is a loss of field when the image erector is used (from 54’ down to 47’ with the 40x eyepiece), the lever that changes from finder to a high power view is disabled, and you can only change powers by changing eyepieces, as the Barlow and finder optics are no longer in the optical path.

This broadband coated version has high transmission/low reflection broadband multicoatings on its objective lens, rather than the standard Field Model’s single layer magnesium fluoride antireflection lens coatings. In addition, the mirrors are coated with high reflectivity silver, rather than the aluminum coatings of the standard Field Model. Compared to the standard #QF Field Model, this broadband multicoated version gives you a full 22% higher light transmission and increased contrast that’s very useful for twilight viewing and photography. Broadband coatings are not recommended for those who live full time at the seashore, however, as a constant exposure to salt air can cause the silver mirror coatings to deteriorate. Occasional exposure to salt sea air on vacations or field trips is not a problem.

In addition, a thermally-stable Zerodur ceramic mirror is used in place of the standard model’s Pyrex mirror for critical photographic situations that don’t allow focus changes during wide temperature swings. (If the temperature differential between indoors and outdoors is 30 degrees to 40 degrees Fahrenheit or more, occasional minor refocusing will be required with the standard Field Model as its Pyrex mirror gradually cools down to reach the outdoor air temperature.) A Zerodur mirror eliminates such minor refocusing in the Arctic or Sahara, but is usually not needed in the continental United States or Hawaii, as well as in most of Canada.

A foam-fitted waterproof hard case is standard equipment.

The Field Model has a ten-year Questar warranty (with a two-year warranty on the focuser mechanism and a five-year warranty on the broadband coatings).

As the review in Audubon concluded simply, “Questar is superb.” If you want the world’s very best spotting scope, this Questar Field Model with broadband coatings and a Zerodur mirror is it. Period. Case closed.

Magnification is the ability of a telescope to make a small, distant object large enough to examine in detail. If you look at the Moon (250,000 miles away) with a 125 power (125x) telescope, it's essentially the same as looking at it with your bare eyes from 2000 miles away (250,000 ÷ 125 = 2000). The same telescope used terrestrially will make an object one mile away appear to be only 42 feet away (5280 feet ÷ 125 = 42).
The magnification of a telescope is determined by dividing the focal length of the telescope (usually in millimeters) by the focal length of the eyepiece used (again, usually in millimeters; but in all cases by the same unit of measurement used for the telescope focal length). For example, a 2000mm focal length telescope and a 10mm focal length eyepiece will give you a magnification of 200 power (2000 ÷ 10 = 200). The same 2000mm telescope with a 20mm eyepiece will give you 100x (2000 ÷ 20 = 100).
Field of view 1000 yards:
46' @ 53x
Near Focus:
Eye Relief:
Eye relief is the distance from the last surface of the eye lens of an eyepiece to the plane behind the eyepiece where all the light rays of the exit pupil come to a focus and the circular image is formed, sometimes called the “Ramsden Disk.” This is where your eye should be positioned to see the full field of view of the eyepiece. If you must wear glasses because of astigmatism, you’ll usually need at least 15mm of eye relief or longer if you want to see the full field of view with your glasses on.

A note on our eye relief figures: Quite often, our eye relief figures will differ from those of the manufacturer. This is because we measure the “usable” eye relief, while the manufacturers specify their usually-longer (but technically correct) “designed” eye relief.

The eye lens of the eyepiece is normally recessed below the rubber eyeguard or rubber rim of the eyepiece to keep the lens from being scratched during use. An eyepiece might have a “designed” eye relief of 15mm (and the eye relief will truly measure 15mm from the eye lens to where the image forms). However, if the eye lens is recessed 3mm below the eye guard, the Ramsden Disk forms only 12mm above the eyepiece body (the 15mm “designed” eye relief, less the 3mm of eye relief made unusable by having the eye lens recessed into the body of the eyepiece). This “usable” eye relief of 12mm (measured from the rolled-down eyeguard – the closest point you can get your eye to the eye lens – to where the image forms) is the eye relief figure we would measure and list in this website.

Why is it important to list the “usable” eye relief? For those people who don’t wear eyeglasses while observing, a few mm difference between the eye relief they expect from the manufacturer’s literature and the shorter eye relief they actually get in real life doesn’t mean a lot. They can simply move a little closer to the eyepiece to see the full field, and never realize that the eye relief is a little shorter than they expected. However, some people must wear eyeglasses while observing, because of severe astigmatism. These observers can’t move closer to the eyepiece if the eye relief is shorter than expected because their glasses get in the way. For these people, the real life “usable” eye relief is more important than the technically correct but sometimes not fully usable “designed” eye relief. We measure and list the actual usable eye relief so that people in the real world can pick the eyepieces that will work best for them.

Exit Pupil:
The circular image or beam of light formed by the eyepiece of a telescope. To take full advantage of a scope's light-gathering capacity, the diameter of an eyepiece exit pupil should be no larger than the 7mm diameter of your eye's dark-adapted pupil, so that all of the light collected by the telescope enters your eye. (The eyepiece exit pupil diameter is found by dividing the eyepiece focal length by the telescope focal ratio.) Your eye's ability to dilate declines with increasing age (to a dark-adapted pupil of about 5mm by age 50 or so). For those in this age group, eyepieces with exit pupils larger than their eyes can dilate to simply waste their telescope's light-gathering capacity, as some of the scope's light will fall on their iris instead of entering their eye.
1.7mm @ 53x
Twilight Factor:
A number used to compare the effectiveness of binoculars or spotting scopes used in low light. The twilight factor is found by multiplying the size of the objective lens (in mm) by the magnification and then finding the square root of that result. The larger the twilight factor, the more detail you can see in low light. A twilight factor of 17 or better if usually required for reasonable low light use.
68.7 @ 53x
This is the diameter of the light-gathering main mirror or objective lens of a telescope. In general, the larger the aperture, the better the resolution and the fainter the objects you can see.
A binocular or spotting scope whose body is clad in rubber or polyurethane armor is said to be armored. Armor can be applied for looks, a better grip, noise-proofing, etc. An armored body does not guarantee that a binocular or spotting scope is waterproof, although most waterproof optics are armored.
Photographic Focal Length:
The effective focal length of a spotting scope/camera adapter combination when the scope is used as a telephoto lens. The photographic focal length divided by 50 will give you the magnification of the combination compared to your standard camera lens.
Photographic Focal Ratio:
The photographic “speed” of a spotting scope/camera adapter combination when used for photography. The smaller the “f/ratio,” the faster the exposure (to capture birds in motion), or the dimmer the light level in which you can successfully shoot.
10 years
There are currently no Cloudy Nights reviews associated with this product

User Ratings/Reviews from our Customers (
Overall Product Rating: AstronomicsAstronomicsAstronomicsAstronomicsAstronomics(0.00)   # of Ratings: 0   (Only registered customers can rate)

We haven't recommended any accessories for this product quite yet... check back soon or call one of our experts (1-405-364-0858).
  • High transmission/low reflection broadband multicoatings
  • Low expansion Zerodur ceramic mirror
  • Eyepiece
  • Built-in 1.5x Barlow and 4x finder
  • Lens shade
  • Camera adapter
  • Dust covers
  • Hard case
No documents have been associated with this product.
No videos have been associated with this product.
There are currently no formulas associated with this product
Questar - Field Model, 90mm, broadband coatings, Zerodur mirror, 53/80x, case

Click icon(s) below & hover image above for zoom

Questar - Field Model, 90mm, broadband coatings, Zerodur mirror, 53/80x, case
   · No ratings/reviews   Only registered users can submit ratings - Register Here
Our Product #: QFBZ
Manufacturer Product #: 10310
Price: $4,225.00  FREE ground shipping - Click for more info
Congratulations. Your order qualifies for free ground shipping within the 48 contiguous United States.

 E-mail this product to a friend E-mail this product to a friend

Your Email:  
Your Friend's Email:  
Confirm Friend's Email:  

  200 characters or less

An email containing a link to this product has been sent to the email address you provided.

Clear Skies!

 Have a question? Do you have a question about this product?
 Found a better price? Found a lower price? Click to let us know... or call 800-422-7876 before you buy.

If you’ve found a lower delivered price on this product, let us know about it below. We’ll do our best to meet or beat that price and will get back to you within one business day with our best offer. Thanks for giving us the opportunity to give you a better deal.

Your Name:  
From Who:  
Context:  Magazine AdOnline
Website Address:  
Cut and paste the web address into the box above
Your Email:  
Confirm Email:  

We’ll do our best to meet or beat that price and will get back to you within one business day with our best offer. Thanks for giving us the opportunity to give you a better deal.

Clear skies,

With all due respect to the other spotting scopes shown on this site, there can only be one "best spotting scope in the world." This Questar Field Model is it . . .

. . . our 38th year