Vortex Viper HD 15-45x65 Angled Spotting Scope

Optical design:

Optical design

Reflector telescopes use a pair of large and small mirrors to direct incoming light to the eyepiece. Refractor telescopes refract, or "bend" incoming light to a focus by means of an objective lens. Cassegrain telescopes, such as Maksutov-Cassegrains, "fold" incoming light using two mirrors and a front "corrector" lens.

Refractor
Magnification:

Magnification

Also commonly referred to as "power", magnification is a measure of how much closer an object appears when viewed through the instrument. For example, a 10x binocular will make an object appear 10-times closer than it would normally appear. An object positioned 100 yards away would appear as if it was just 10 yards away in a binocular with 10x magnification. The human eye is considered 1x magnification.

15x - 45x
Optical diameter:

Optical diameter

For telescopes, the optical diameter (also known as aperture) is the size of a telescope's main light-collecting lens or primary mirror, measured in millimeters or inches. Telescopes with larger optical diameters collect more light, which leads to an increase in brightness and image resolution compared to smaller instruments.

For binoculars, the optical diameter (also known as objective lens diameter) is the size of each of the front-facing objective lenses of a binocular measured in millimeters. Binoculars with larger objective lenses collect more light, which increases image resolution and brightness. Binoculars with larger objective lenses are recommended for low light situations, and binoculars with at least 50mm or larger objective lenses are recommended for pleasing astronomical observations at night.

65mm
Field of view - angular:

Field of view - angular

The field of view expressed as part of a 360-degree circle. Holding your pinky finger out at arms length is approximately 1-deg wide. To convert this to the linear measurement of "feet at a thousand yards", multiply by 52.5. For example, at 1000 yards distance, a 7-deg binocular will see a width of 367.5 feet (7 x 52.5)

2.6° - 1.3°
Field of view - linear:

136.5 - 67.8 ft./1000 yd
Eye relief:

Eye relief

The distance, measured in millimeters, between the observer's eye and the eyepiece lens in which the entire field of view remains visible. Eye relief varies with the optical design but generally increases with decreasing magnification. Long eye relief is advantageous for observers who wear glasses, as they don't have to put their eye directly on the eyepiece to see the entire field of view, nor do they have to remove their eyewear.

19.6mm
Exit pupil:

Exit pupil

The diameter of the circle of light exiting the binocular. Exit pupil is calculated by dividing the objective lens diameter by the binocular magnification. For example, a 10x50 binoculars has an exit pupil of 5mm (50/10=5). Knowing the exit pupil of a binocular can help determine the optimal binocular fro your needs. If a binocular exit pupil is larger than the dilation of the user's pupil, resolution is reduced since the maximum amount of light is not entering the eye. Typically under true dark adaptation a healthy human eye will dilate to approximately 7mm. This number can decrease with age and health factors.

0.1mm
Near focus:

Near focus

The minimal distance at which a binocular and/or spotting scopes can attain focus. Near focus is an important quality for bird watchers and wildlife devotees who want to get as close as possible to their quarry.

23 ft.
Coatings:

Coatings

Binocular lenses and prisms are often coated with anti-reflective material to minimize light loss as light travels through the multiple optical surfaces of a typical binocular. Coatings help maximize the amount of light transmitted through each glass surface of a binocular, so as much light as possible reaches the observer's eyes to provide a bright and sharp image.
Good lenses are at least "fully coated," with a single layer of magnesium fluoride coating applied to each air-to-glass lens surface. Multiple layers of coatings are even more effective; the term "multi-coated" means one or more air-to-glass lens surface has multiple coatings. "Fully multi-coated" optics are even better, meaning all lens surfaces have multiple layers of anti-reflective coatings applied for maximum light transmission and optimal image quality.

Dielectric
Lowest useful magnification:

Lowest useful magnification

Lowest useful magnification is the power at which the exit pupil becomes 7mm in diameter. Powers below this can still be reached with the telescope to give wider fields of view, but the image no longer becomes brighter at a lower power. This is due to the fact that the exit pupil of the telescope (the beam of light exiting the eyepiece) is now larger than the average person's dark adapted pupil, and no more light can fit into the eye.

15x
Highest useful magnification:

Highest useful magnification

The highest practical limit is different from the often used "highest theoretical magnification" specification. The "theoretical" limit generally is 50x the aperture of the scope in inches (2x the aperture in mm). So for example, an 80mm refractor is capable of 160x, and a 10" telescope is theoretically capable of 500x magnification. But after approximately 300x, theory breaks down and real world problems take over. The atmosphere above us is constantly in motion, and it will distort the image seen through the telescope. This effect may not be noticeable at lower powers, but at higher powers the atmosphere will dramatically blur the object, reducing the quality of the image. On a good night (a night where the air above is steady and the stars aren't twinkling), the practical upper limit of a large telescope is 300x, even thought the theoretical limit may be much higher. This doesn't mean the scope will never be able to reach those higher "theoretical" powers - there will be that rare night where the atmosphere is perfectly still and the scope can be pushed past it's practical limit, but those nights will be few and far between.

45x
Eyepiece angle:

45°
Camera adaptable:

Yes
Waterproof:

Yes
Tripod adaptable:

Yes
Mount type:

Optical Tube without Mount
Length of optical tube:

14.0 in.
Weight, optical tube:

3.7 lbs.
Additional included accessories:
Other features:

Eyepiece cap, Objective Lens cover, Custom Fitted Case
Warranty:

Warranty

This warranty gives you specific legal rights. It is not intended to remove or restrict your other legal rights under applicable local consumer law; your state or national statutory consumer rights governing the sale of consumer goods remain fully applicable.

Unlimited lifetime

Optical design

Magnification

Optical diameter

Field of view - angular

Eye relief

Exit pupil

Near focus

Coatings

Lowest useful magnification

Highest useful magnification

Warranty