8.5X44mm Audubon ED porro prism waterproof

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The first Swift Audubon binocular was designed for Swift by Mr. Tamura of the Tamron optical company in Japan from specifications gleaned from a Swift survey of the world’s leading ornithologists. Since then, there have been three versions of the Swift Audubon produced using the same optical formula, which has become world famous for its superior performance and dependability. This newest ED version of the 8.5 x 44mm Audubon is a step up even from the superb optics of the standard Audubon.

This new Audubon uses an objective lens element of the same premium ED (extra-low dispersion) fluorophosphate glass used in expensive camera lenses. This ultra-premium glass gives you 5-10% better contrast and color saturation than the standard Swift Audubon porro prism, without giving up any of that world-famous binocular’s brightness or clarity. In addition, the new Audubon ED adds a new lightweight armored body and waterproofing.

There is much to be said for the Audubon’s 8.5x magnification, compared to the more common 8x. The extra half-power gives you the extra reach you sometimes need to make a positive identification on a distant bird. It also gives you a slightly larger image of a close-in bird to add to your enjoyment. And it does both without adding so much extra magnification that the image becomes hard to hold still enough to see sharply (go much over 9x in a hand-held binocular and the image bounces around with every breath and muscle tremor). The Audubon’s 44mm aperture gives you 21% greater light-gathering than a 40mm bino for images that are bright and high in contrast – even in the low light of early morning or twilight.

The Audubon is a center focus B-body porro prism with premium fully-multicoated BaK-4 prisms for highest light transmission and contrast. The lightweight magnesium body is sealed to be waterproof, although it is not nitrogen-purged and so is not guaranteed to be fogproof in all climate extremes. The Audubon might not survive full immersion for long periods, but it is certainly watertight enough to come in dry when you get caught outside in a heavy rain. It should even survive tropical use with moderate care.

The rubber armor is firm enough for a secure grip, resilient enough for long-term comfort, and lightly textured so your fingers won’t slip. There are provisions for adding an optional tripod adapter #1187 for extended no-hands viewing from a fixed observing location.

The Audubon ED comes with a soft case, a 1.5” wide woven neck strap, twist up rubber eyecups, and objective lens covers. Eyepiece covers are standard, rather than an eyepiece rainguard.

The Audubon’s premium five-element eyepieces give you a wide field of view with relatively little field curvature. The 8.5x Audubon has an excellent delineation of details in the center of the field due to the somewhat higher resolving power of its larger aperture optics vis-a-vis competitively priced 40mm and 42mm binoculars.

The Audubon ED does have somewhat limited eye relief. Eye relief is the distance behind the eyepiece that your eye has to be to see the full field of view. It is important for eyeglass wearers, who can get no closer to the binocular eyepieces, obviously, than the distance between their glasses and their eyes. Swift claims 17mm of eye relief for the Audubon, which should be plenty for an eyeglass wearer. However, while this eye relief is technically correct, the actual usable eye relief of the Audubon ED is closer to 13mm than it is to 17mm, due to the somewhat recessed location of the eyepiece (designed that way to keep eyeglasses from making contact with the eyepiece lens during use, with the possibility of scratching either or both lenses). The 13mm of usable eye relief will somewhat narrow the field of view for eyeglass wearers.

However, this somewhat short eye relief is compensated for by a wider field than competitive binoculars (so wide that it’s almost impossible to see the entire field without looking from side to side – even without glasses). The result is that the usable field of the 8.5 x 44mm Audubon with glasses is often similar to competitive longer eye relief binoculars without glasses.

If you want a little bit more optical performance than is normally reasonable to expect in a porro prism binocular in this price range, the Swift Audubon ED binoculars give you exactly what you’re looking for – at a price well within reach and reason.

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).
Porro Prism
Field of view:
The field of view (FOV) is the amount of observable world one can see at any given moment.
Field of view 1000 yards:
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.
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.
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.
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.

Interpupillary Distance:
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
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.
The weight of this product.
27.5 oz
25 years
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Tripod adapter for both roof and porro prism binoculars
by Celestron
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Swift - 8.5X44mm Audubon ED porro prism waterproof

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Swift - 8.5X44mm Audubon ED porro prism waterproof
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Our Product #: SW8544E
Manufacturer Product #: 820ED
Price: $599.95
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MSRP: $599.95

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NEW CLOSEOUT  VERY LIMITED QUANTITIES AT THIS PRICE! If you want a little bit more optical performance than you'd normally expect in a porro prism binocular in this price range, the vanishingly low spurious color of the ED glass optics in these Swift Audubon ED binoculars will give you exactly what you’re looking for – at a price well within reach and reason . . .

. . . our 37th year