8.5X21mm Papilio butterfly binocular

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The Papilio 8.5 x 21mm close focuses to a mere 26 inches or less. Pentax specs it at 26”, but we typically measure it focusing as close as 20”. We can’t guarantee this latter measurement for your eyesight, however, so we’ll stick to quoting Pentax’s more conservative 26” close focus in our specifications. The Pentax Convergent Lens Optical System Engineering (CLOSE) mechanism automatically slides the left and right objective lenses toward the center as you focus at shorter and shorter distances. This special converging lens system keeps you from getting eyestrain or a headache when trying to focus very close.

At a 26” close focus, using the 8.5 x 21mm Papilio is the same as getting your eye within 3” of the butterfly or bug, with a field of view 2.7” across. Identifications are a snap.

The optics are fully multicoated to eliminate harmful ultraviolet rays while improving light transmission. This gives you high contrast images with no glare or flare. The Papilio uses high quality BaK-4 prisms to transmit more light at the edges of the field. This enhances the illumination for easier viewing in dim light. The body is a reverse porro prism design, in which the objective lenses are closer together than the eyepieces. This allows for nearly full-size binocular performance from a very compact body. A soft touch dark grey rubber armor with molded-in thumb grooves covers the durable and lightweight molded polycarbonate body to protect the internal mechanisms and provide a sure grip.

An eighth of a turn of the twist-up rubber-rimmed eyecups retracts them into the binocular body for eyeglass or sunglass use, rather than rolling down. This eliminates the possibility of the eyecups drying out and cracking with age and use, as with conventional rolldown eyecups. An eighth turn in the opposite direction extends the eyecups for non-eyeglass use. Eye relief is specified at 15mm. While this is technically correct, the actual usable eye relief typically measures a mm or two less due to the recessing of the eyepieces when the eyecups are in the down position for eyeglass use. A shorter eye relief than specified is typical of all binoculars. There will be some vignetting of the field for eyeglass wearers. The diopter adjustment on the right eyepiece is a click-stop design that won’t accidentally get out of adjustment when you least want it to. Focusing is somewhat slow, at three turns from close focus to the horizon, but extremely precise for close-in focusing.

For extended hands-free viewing from a fixed position, you can mount the Papilio on a camera tripod using an optional tripod adapter and the standard 1/4”-20 thread tripod socket located underneath the binocular body. The supplied soft case has a belt loop for no-hands carrying. The woven neckstrap is 3/4” across, not exceptionally wide, but more than comfortable for all-day use with the lightweight (10.2 oz.) Papilio. An eyepiece rainguard completes the supplied accessories.

Aside from its manifest virtues as a butterfly binocular, the Papilio is a handy bino for nature walks, hiking, traveling, spectator sports, the theatre, etc. – anywhere compact size, good optics, and light weight are important.

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:
315'
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.
2.47mm
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.
6.10
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.
13.36
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:
56-74mm
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
26"
Height:
4.6"
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.
10.2 oz.
Warranty:
Limited Lifetime
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  • Soft case with belt loop
  • Neck strap
  • Eyepiece rainguard
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Pentax - 8.5X21mm Papilio butterfly binocular

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Pentax - 8.5X21mm Papilio butterfly binocular
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Our Product #: P8521
Manufacturer Product #: 62216
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This 8.5x Pentax Papilio, named for the Latin word for butterfly, is the first binocular designed specifically for truly close-up views of butterflies – or insects, or birds, or museum artwork, or anything else you want to get closer to than the beastie or museum guard will allow . . .





. . . our 34th year