8.5X44mm Audubon HCF roof prism waterproof

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For those birders with small hands who love the optics of the Swift Audubon porro prism binoculars, but who find their shape and weight a little bulkier than they care to carry, Swift has developed the new 8.5 x 44mm Audubon roof prism. It has the roof prism’s user-friendly slim tube design, and is a full quarter-pound lighter than its porro prism brothers. Even so, it has the same power and aperture as the world-famous porro prism Audubons.

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 10% higher resolution and 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 optics are quite good, although with a small loss in brightness compared with the same size Audubon porro prisms. Most observers feel that the lighter weight and more compact shape more than makes up for the slight light loss.

The Audubon roof is a fully-multicoated center focus H-body roof prism, with phase-coated BaK-4 prisms, 1.5” wide comfort woven neck strap, eyepiece rainguard, and a soft case to shed sudden showers. It is sealed and nitrogen-purged to be fully waterproof and fogproof in all climate extremes.

The body is clad in rubber armor that is firm enough for a secure grip, resilient enough for long-term comfort, and lightly textured so your fingers won’t slip. Strategically-placed thumb grooves on the underside of the binocular help position the hands in the optimum position to operate the focus knob. Focusing is a trifle slow, at two turns from near focus to the horizon, but the large knurled focus knob works very lightly and smoothly, so even rapid focus changes are not a chore. Eye relief is a good 19mm for virtually unvignetted eyeglass views. Pop-up rubber-rimmed eyecups allow quick changes between eyeglass and non-eyeglass use for those who share a binocular. A soft click-stop diopter adjustment on the right eyepiece lets you adjust the binocular for your individual eyesight.

A review of the Audubon roof in Better View Desired said, “They are compact, light weight, and well balanced. The focus is smooth: on the slow and precise side rather than the finicky side of the average for roofs. Physically, I can't imagine a more attractive or field worthy glass . . . Optically, the new glass holds its own . . . It does not equal either the brightness or resolving power of the 8.5x44 porro (or of the 8.5x42 Swarovski EL for that matter) but it comes very, very, close . . . Looked at from one side this performance means that you can get 8.5 power and the handling of a roof in the Audubon line without sacrificing noticeable optical performance. Looked at from the other it means that you can get an 8.5x binocular with almost the performance of the Swarovski EL (and perhaps a shade better handling, considering weight, size and focus) for considerably less money . . . the Audubons may just represent the current "best buy" in a roof prism binocular. They do for roofs what the porro Audubons did for porros: provide a real birdworthy glass at a price most of us can afford, and, being roofs, they do it in a much more elegant (and somewhat more fieldworthy) package. The 8.5x44 Audubon roofs are worthy of the Audubon (and the Swift) name: a joy to carry and use, and providing a view of the bird that will satisfy the most demanding birder.”

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.
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.
24 oz
25 years
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Swift - 8.5X44mm Audubon HCF roof prism waterproof

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Swift - 8.5X44mm Audubon HCF roof prism waterproof
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Our Product #: SW8544R
Manufacturer Product #: 828
Price: $359.95  FREE ground shipping - Click for more info
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MSRP: $499.95

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Clear skies,

For those birders with small hands who love the optics of the Swift Audubon porro prism binoculars, but find them a little bulkier than they care to carry, Swift has developed the 8.5 x 44mm Audubon roof prism . . .

. . . our 35th year