10X42mm Horizon roof prism

by Swift Print

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This high power Swift 10 x 42mm Horizon roof prism binocular weighs only 26.8 ounces, surprisingly light for a full-size binocular. It is armored and nitrogen-filled to be fully waterproof and internally fogproof in all climate extremes. The Horizon’s compact 5.5” length is easy to handle, and its light weight won’t weigh you down during all-day birding. This is an easy-to-carry all-day/all-weather long distance birding bino.

Although it will close focus to less than 5’, the Swift 10x Horizon is happiest when examining the details and colors of birds at intermediate distances and across open fields, lakes, and during shore-side birding. The high contrast of its phase- and silver-coated roof prisms and the good resolution and bright images of its fully-multicoated 42mm optics reveals enough detail and color in distant birds to make even a seasoned birder happy. This reasonably-priced 10 x 42 Swift Horizon is a surprisingly good high power performer across a wide range of observing conditions, from near to far, from bright sunlight to dim twilight.

Geometric (barrel) distortion is modest, as is curvature of field. Some astigmatism is visible, so that images at the edges of the field are somewhat softer than they are at the center, but images stay usably sharp across most of the good 6.5° field.

Overall, this is an optically and mechanically good high power binocular at a very reasonable price. It’s easy on the eyes, easy in the hands, and easy on the budget.

Features of this binocular . . .

  • Roof prism optics. H-body roof prism design with internal center focus. Top-quality BaK-4 prisms for high light transmission.
  • Large aperture fully multicoated optics. Large 42mm objective lenses gather substantial amounts of light for bright images in twilight or overcast conditions. The twilight factor is 20.49, well above the 17 recommended as a minimum for a low light binocular. The optics are fully multicoated with layers of antireflection materials for good light transmission and minimum light loss in dim conditions.
  • Silver coated prisms. The image-erecting roof prism have a mirrored surface that is coated with high reflectivity silver for neutral color reproduction and high light transmission through the prisms.
  • Phase coated optics. Phase-correcting roof prism coatings provide very high contrast and resolution. This is particularly visible when looking sunwards, where more color and detail are clearly visible in the shadowed areas of backlit or silhouetted birds.
  • Waterproof. The rugged die-cast magnesium alloy body is O-ring sealed and nitrogen filled to be waterproof and internally fogproof in all temperature and climate extremes. The Swift Horizon is designed to operate reliably in rainforests and deserts alike. In addition, the dry nitrogen filling prevents tarnishing of the silver prism coatings for years of unblemished optical excellence.
  • Armor. Fully coated in black rubber armor that absorbs noise and shock and provides a good grip when wet.
  • Good eye relief. Eye relief is specified at 15mm. While this is technically correct, the actual usable eye relief typically measures a millimeter or two less. This is due to the recessing of the eyepiece lenses to protect them from getting scratched when the eyecups are in the down position for eyeglass use. A shorter eye relief than specified is typical of virtually all binoculars. Some vignetting will be visible for those eyeglass wearers who must wear eyeglasses while observing due to severe astigmatism.
  • Twist-up eyecups. The rubber-rimmed eyecups twist counterclockwise to extend and clockwise to retract. There are two soft stops intermediate between the retracted and fully-extended positions to let you match the amount of eye relief to your eyesight. Three eye relief heights are labeled in mm on the eyecup barrels. Since this 15mm eye relief 10 x 42mm Horizon shares the same body as its longer 18mm eye relief 8 x 42mm brother, the eyecups extend further than needed to accommodate the shorter eye relief of this 10x binocular. Observers who do not wear eyeglasses should not extend the eyecups fully. This will place your eyes out past the optimal eye relief distance and will vignette the image. The eyecups should be extended only to the second intermediate soft stop in order to see the full field if you don’t wear glasses.
  • Very close focusing. Little more than one turn of the large focus knob moves from the close focus out to the horizon and beyond. Swift specifies an exceptional 3.9’ as the close focus, but we usually measure it as being closer to 5’ in our tests. A 5’ close focus is still very good for close-in birding and butterflies, although the somewhat shallow depth of field of this 10x Horizon would not make this our first choice for such an application. Like most 10x binoculars, the 10x42mm Horizon is best suited for intermediate and long distance observing.
  • Wide field. The field of view is a quite good 6.5° degrees (342’ at 1000 yards). This is wider than many binoculars more than twice its reasonable price.
  • Rotary diopter correction. A continuously variable diopter ring on the right eyepiece allows you to match the binocular optics to your individual eyesight for the sharpest images. The diopter ring is quite stiff and unlikely to accidentally shift out of position during use.
  • Tripod adaptable. A standard 1/4”-20 thread socket for attaching an optional tripod adapter is located at the front end of the binocular’s center hinge. A thread-in plastic plate covers the tripod socket when not in use.
  • Wide neck strap. The wide neck strap is padded with soft neoprene and cloth-wrapped for more comfortable long-term use in hot weather. It makes the lightweight binocular even less of a burden to carry during all-day birding sessions.
  • Other supplied accessories. A lightly-padded textured soft vinyl case with a belt loop and a shoulder strap is standard. Also included are snap-in objective lens covers to protect the optics during transport and storage and an eyepiece rainguard.
  • Optical Type:
    The optical design of a binocular or spotting scope. A binocular can be either a porro prism (whose objective lenses are off-set and spaced further apart than the eyepieces) or a roof prism (whose objective lenses are in line with the eyepieces). A spotting scope can be either a porro prism or roof prism refractor or a catadioptric (a combination of lenses, mirrors, and prisms).
    Roof Prism
    Field of view:
    The field of view (FOV) is the amount of observable world one can see at any given moment.
    6.5°
    Field of view 1000 yards:
    342'
    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.
    4.2mm
    Relative Brightness:
    A number used to compare the brightness of binoculars or spotting scopes of similar magnification. The relative brightness is determined by squaring the diameter of the exit pupil. The larger the relative brightness number, the brighter the image.
    17.64
    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.
    20.49
    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.

    15mm
    Interpupillary Distance:
    58-73mm
    Close Focus:
    How close you can get to an object and still see a sharp image of it in your binocular or spotting scope is called the “close” or “near” focus
    3.9'
    Height:
    5.5"
    Armored:
    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.
    Yes
    Weight:
    The weight of this product.
    26.8 oz.
    Warranty:
    25 years
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    • Soft case
    • Neck strap
    • Objective lens covers, eyepiece rainguard
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    Swift - 10X42mm Horizon roof prism

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    Swift - 10X42mm Horizon roof prismImage showing the binocular with all supplied accessories. The eye relief heights are visible on the eye cup barrels.
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    Our Product #: SW1042H
    Manufacturer Product #: 920
    Price: $199.95  FREE ground shipping - Click for more info
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    This high power 10 x 42mm Swift Horizon has the features you want in a high power roof prism binocular – plus an unexpectedly reasonable price . . .





    . . . our 34th year