General knowledge_Shenzhen Skyoptikst Optical Technology Co., Ltd.


General knowledge

1. Astronomical Telescope Tech

Aperture (Diameter)

The clear aperture of a telescope lo thediameter of the objectlve lens or prmary"mirror specified elther in Inches or millimeters. The larger the aperture, themore light it collects and the brighter(and better) the image will be. Greaterdetail and image clarity are observed asaperture increases.

Focal length

This is the distance (usually speclfied inmillimeters) from the lens (or primarymirror) to the point where the telescopeis in focus(known as the focal point) inan optical system. Generally speaking,the longer the focal length of the telescope is, the more power t has, andthe larger the image and the smaller thefield of view will be.

Focal Ratio

Focal ratio is the focal length of anobjective divided by the effectiveaperture diameter. For example, thef/ratio of a telescope with a 200mm aperture and a focal length of 1000mmis: 1000/200=5, or f/5. The larger thefocal ratio is, the longer the focal lengthis for the same aperture telescopes; andthe larger the power is and the dimmerthe field is for identical eyepieces.Select the focal ratio according to thepower you desire In other words,decide on the observing objects first.Though the power can be adjusted bychanging eyepiece, the selections ofeyepieces and focal lengths are limited.It is also necessary to check whetherthe focal ratio is reasonable for theaperture to make sure the power doesnot exceed the effective power toomuch. Generally speaking, it is best toselect the moderate one.


The magnification of a telescope is thefocal length of the objective divided bythe focal length. of the eyepiece.Namely, mågnification = focal length ofthe objective in mm 1 focal length of theeyepiece in mm. The longer the focallength of the objective is and theshorter the focal length of the eyepieceis, the arger the magnificationis. Themost common misunderstanding of ,telescopes is that they are rated bytheir magnifying power, The fact is,telescopes are rated by their apertureor light gathering capability, Theaperture of a telescope is far more important than its power, because itdetermines the telescope's ability toresolve small or distan objects.

Light Gathering Power

The light gathered by dark adaptednaked eye has the largest entrancepupil (the largest entrance pupils arefrom 6mm to 7mm). At night, the lightgathering power ofthe eye = "1" (for7mm). For telescopes, the light gathering power is determined by theaperture of the objective. Light gathering power = (the objective

diameter (in mm) 1 entrance pupil of andark adapted eye (= 7mm))2. Thelarger the aperture is, the more light itcollects, and the better the image is.

Limiting Magnitude

Limiting magnitude is the faintestapparent star magnitude that can bedetected through a specific telescope.Telescopes have higher light gathering abilitythan the naked eye, so you can see fainter starsthat are not visible with the unaided eye. Thefaintest star you can see with your unaided eyesis about magnitude 6, whereas the faintest star a50mm telescope can see is magnitude 10.3 under dark skies. The larger the aperture is, thelarger the limiting magnitude is. However, thelimiting apparent magnitude of the sky (affectedby light pollution) may impose further limitationon what can be detected.


Resolution can be defined as the ability of a telescope to render fine details. It is measured interms of degrees, minutes of arc (arc-minutes),and seconds of arc (arc seconds). is directlyrelated to the objective entrance pupil. The largerthe entrance pupil diameter (the aperture of theobjective) is, the higher the resolution is, andthemore details you can see. A method that is oftenused to measure resolution is to split two veryclose stars (double stars)

2. Binocular Tech

Prism Systems

The prism system of a binocular reduces the size needed to contain a long optical path and turns what would be an upside-down image right-side-up. There are two types of prism systems, roof and porro.

Roof Prism System

In roof prism binoculars, the prisms overlap closely, allowing the objective lenses to line up directly with the eyepiece. The result is a slim, streamlined shape in which the lenses and prisms are in a straight line. Roof prism binoculars are less bulky and more rugged than an equivalent porror model.

Porro Prism System

In porro prism binoculars, the objective or front lens is offset from the eyepiece. Porro prism binoculars provide a greater depth perception and generally offer a wider field-of-view. Because of the simplicity of this system, some of the best values can be with a porro design.

Field-of-View (F.O.V.)

The side-to-side measurement of the circular viewing field or subject area. It is defined by the width in feet or meters of the area visible at 1000 yards or meters. A wide field-of-view makes it easier to spot game and track moving targets. Generally, the higher the magnification, the narrower the field-of-view.

Exit Pupil

Refers to the size of the circle of light visible at the eyepiece of a binocular. The larger the exit pupil, the brighter the image. To determine the size, divide the objective lens diameter by the power (an 8x32 model has an exit pupil of 4mm).

Coated Optics

Lens surface coatings reduce light loss and glare due to reflection for a brighter, higher-contrast image with less eyestrain.

Eye Relief

The distance a binocular can be held away from the eye and still present the full field-of-view. Extended or long eye relief reduces eyestrain and is ideal for eyeglass wearers.

Types of Coatings:

Coated - A single layer on at least one lens surface.
Fully Coated - A single layer on all air-to-glass surfaces.
Multi-Coated - Multiple layers on at least one lens surface.
Fully Multi-Coated - Multiple layers on all air-to-glass surfaces.

Some binoculars are O-ring sealed and nitrogen-purged for total waterproof and fogproof protection. These models can withstand complete immersion in water and stay dry inside. The interior optical surfaces won't fog due to rapid temperature change or humidity. Such as our 8x32F is 100% waterproof and fogproof.

Magnification (Power)

Binoculars are often referred to by two numbers separated by an "x". For example, 8x32. The first number is the power of magnification of the binocular. With an 8x32 binocular, the object being viewed appears to be eight times closer than you would see it with the unaided eye.

Objective Lens Size

The second number in the formula (8x32) is the diameter of the objective front lens. The larger the objective lens, the more light that enters the binocular and the brighter the image.

Prism Glass

Most optical prisms are made from borosilicate (BK-7) glass or barium crown (BaK-4) glass. BaK-4 is the higher quality glass yielding brighter images and high edge-to-edge sharpness.


Resolution, or definition, is the ability of a binocular to distinguish fine detail and retain clarity.

Eyeglass Wearers - Eyecups

The distance a binocular can be held away from the eye and still present the full field-of-view. Extended or long eye relief reduces eyestrain and is ideal for eyeglass wearers.

Diopter Adjustment

A "fine focus" adjustment ring usually provided around one eyepiece to accommodate for vision differences between the right and left eyes.

Rubber Armor

Rubber armor provides multiple benefits. It helps protect the binocular from the bumps and scratches that come with day-to-day use. It provides a comfortable gripping surface for making them easier to hold on to. It's easy to wipe clean after a tough day in the field. And it suppresses noise if the binocular bumps aluminum or other non-rubber surfaces, which might otherwise spook wildlife.

3. Spotting scope Tech


A spotting scope is a small telescope that has been modified for use by day. A spotting scope differs from an astronomical telescope in several important ways. First, a spotting scope always produces an upright image whereas a telescope used in astronomy may produce a reversed image or even an upside down image (not a problem for astronomy). Second, a spotting scope is much smaller in size than an astronomical telescope, mainly for the sake of portability. Third, a spotting scope is a lower magnification instrument than a telescope, since the atmosphere by day does not allow the high magnifications used in astronomy. Fourth, a spotting scope is mounted on an ordinary photo tripod, but a telescope for astronomy requires a very specialized mount, often unsuitable for daytime use. Lastly, many, if not most, spotting scopes are waterproof and fogproof - a rare feature in an astronomical telescope.


Spotting scopes are used anytime you need more magnification than a binocular provides. Spotting scopes are widely used for birding, surveillance, hunting, and viewing landscape, wildlife, ships and other distant objects. Spotting scopes are also used for scoring targets on rifle, pistol and archery ranges and they can also be used to some astronomy. Last, but not least, spotting scopes are also used to take long distance pictures with a variety of cameras.


Spotting scopes begin in magnification where conventional binoculars stop. The higher magnifications offered by a spotting scope allow you to view birds, wildlife, scenery and other objects that are well beyond the range of a conventional binocular. However, there are limits to magnification. Two things determine how much magnification you can use in a spotting scope.

The first is the atmosphere. You must always factor in the seeing conditions of the atmosphere when using a spotting scope. Heat waves, dust, humidity, glare, wind and air currents during the day all reduce image quality and the greater the magnification, the more drastic the reduction in image quality. Simply put, there will be days when anything over 30x will appear as mush, but there will also be those clear, calm days when you can use 60x to good advantage. In general, high altitudes and dry climates favor high magnification whereas wet, humid, low-altitude climates discourage high magnification. Very few locations, however, allow you to use more than 60-80x during the day, so most spotting scopes stop at 60x. Many beginners make the mistake of buying an astronomical telescope that can magnify hundreds of times for day use, only to discover that the atmosphere still limits them to around 60x and quite often, much less.

The atmosphere, for the same reason, also limits how much detail you can see at great distances. Seeing tiny detail, such as a person's facial features, at a mile or more through an ocean of turbulent, ever-moving air is simply not possible, no matter how much magnification you use or no matter how large or expensive the instrument. Spotting scopes are great, but they can't work miracles. On the other hand, it is quite possible to view large objects such as ships at this distance, though the image may be blurry or wavy.

The second major limit on magnification is the optical system of the spotting scope, itself. Regardless of the model, there will always be some drop off in image quality as magnification goes up. This is determined somewhat on the design and size of the scope, but primarily on the quality of the optical system. Here you get what you pay for in a very visible way. Inexpensive spotting scopes, regardless of size or type, lose image quality quickly as magnification goes up, but premium grade scopes lose very little in image quality, even at the highest magnification. Be prepared to pay, however, if you want a spotting scope that is as sharp at 60x as it is at 20x. Only a handful of very expensive spotting scopes are capable of this.

Most observing with a spotting scope, though, is done at lower magnifications, usually around 30x-40x. This is more than enough for most applications and all but the cheapest model will produce reasonable images in this magnification range.

Objective Size

The larger the objective lens, the more detail you can see and the better image quality your scope will deliver, especially at higher magnifications, assuming you are comparing two models of similar quality. However, a large lens of mediocre quality, no matter how large, will never equal the performance of a smaller, quality lens. When in doubt, go for quality, not size.

You can also improve the performance of any spotting scope, especially at higher magnifications, with special quality glass (ED glass, APO glass, HD glass, Fluorite glass) in the objective. This option will cost you more, but it can deliver image quality on a par with a larger objectives made of standard glass. If portability is an issue, a smaller model with ED glass other special glass may be all the spotting scope you will ever need.

If you need the absolute best in performance, however, there is still no substitute for a large, quality objective made with high performance glass.

Prism Type And Telescope Design

Most spotting scopes these days are refractors, the same design used in binoculars and many telescopes. As with a binocular, a prism (inside the spotting scope) is used to turn the image right side up and correct it right to left. Two prism types are used in a refractor style spotting scope.

Porro prism spotting scopes are by far the most common and for good reason. The porro prism design is the most efficient in terms of optics and is also the easiest and least expensive prism to produce. Bak-4 glass is the preferred glass in a porro prism and will be used in all but the very cheapest spotting scopes. BK7 in a spotting scope is a sign of low quality spotting scope.

Roof prism spotting scopes offer the advantage of being slim and compact, but they are not as efficient as a porro prism and usually lack many of the added features of the porro prism design such as interchangeable eyepieces, camera adapters and so on. About the only reason to choose a roof prism spotting scope these days is for applications calling for extreme portability. However, if you expect any kind of performance in a roof prism, you will need to choose a PC (phase-coated) roof prism model.

There are designs other than a refractor to consider. A Maksutov design is sometimes used in a spotting scope and some of these models use the same eyepieces found in astronomical telescopes, making them good choices for people who want to use a scope by day and by night.

Close Focus

Although not an absolute necessity, a spotting scope with a close focus of less than 20 ft can be useful, especially if you plan to use a spotting scope with a camera.

Image Quality

"Keep your expectations in line with price and buy according to your needs," is excellent advice for any optical instrument, but it applies especially to spotting scopes. There is a huge gap in performance and price between low quality scopes and premium grade scopes. For many applications, you can get by with a low or medium priced model, but if you need the performance of a high grade model, there's no getting by cheap. You must pay the price.

Eye Relief

This is the distance your eye can be from the eyepiece and still see the entire field of view. This is an important feature if you wear eyeglasses when you observe or if you are not in a position to get close to the eyepiece. As a general rule, you will need at least 14mm of eye relief to see the entire field of view with eyeglasses and people with thick glass lenses in their eyeglasses will probably need more.


A waterproof spotting scope is not a necessity for many applications, but it is still a good feature to have, even so. The seals in a waterproof model also keep out dust and dirt and therefore add to the lifespan of the spotting scope.

Lens Coatings

Lens coating improve light transmission which is important in a high magnification instrument such as a spotting scope. In order of increasing quality and performance, you will find "fully coated", then "multi-coated", then "fully multi-coated". All premium grade models are fully multi-coated, often with special chemical formulas that vary from manufacturer to manufacturer.


When shopping, be careful. Some spotting scopes include the eyepiece in the price and some do not.

Most low to medium priced spotting scopes include the eyepiece and many of these do not allow the eyepiece to be removed anyway. Higher priced spotting scopes, though, offer removable eyepieces and a selection of eyepieces for different applications. On these models, the eyepiece is often NOT included in the price. When you see a model advertised as "body only" it means just that. You still need to buy an eyepiece and add it to the price of the spotting scope.

Despite some optical advantages to a single power eyepiece, most people prefer the convenience of a zoom eyepiece. This is especially true of applications where there is little time to change an eyepiece to get a better look. A zoom eyepiece also allows you to change magnification quickly and easily as atmospheric conditions change.

Be warned, however, that inexpensive zoom eyepieces are notorious for low image quality and poor eye relief. High grade zoom eyepieces, on the other hand, excel in these two categories, but often cost as much as a mid-priced spotting scope.

Camera Adapters

Many spotting scopes, but not all, are camera adaptable. Much depends on the type of camera being used. SLR cameras (cameras with removable lenses) require very specific adapters, but you can attach a small digital point and shoot camera to nearly any spotting scope with a universal digital adapter such as the Visionking25-75x70. This is called "digiscoping" and is a fun and effective way to take pictures through a spotting scope. Just be sure to measure the diameter of the eyepiece on your spotting scope and order accordingly.


This is a useful feature for a spotting scope which will be seeing hard use out in the field, but not necessary for more casual applications. If you are concerned about scratches, many spotting scopes can also be fitted with an optional zippered nylon case which can be left on the scope when in use.


Choose carefully, here. If you are ever tempted to leave a spotting scope behind due to weight, you may be carrying too much scope. A spotting scope and tripod used from a permanent location or from a vehicle is one thing, but a spotting scope and tripod carried on your shoulder as you hike is quite another. A 60mm or 65mm model also requires less in the way of a tripod, so you can also save weight on this essential piece of equipment as well.


You cannot handhold a spotting scope due to its high magnification. It must be supported to steady it. You can get by at lower magnifications with a monopod or shoulder stock, but above 40x, you must use a tripod and the larger and heavier the scope, the larger and heavier the tripod should be. A car window mount is a viable option, though, if you are observing from a vehicle.

There is no need to buy a special tripod for a spotting scope. All spotting scopes are threaded like a camera and will fit on any standard camera/video tripod.

4. Night Vision Tech

Define night vision

All night vision devices also called NVDs are basically meant to improve the ability to see at night.
The night visions are sophisticated devices that offer assistance while viewing in almost complete darkness situations. Their task is to amplify the available light for easier viewing.
All Visionking night vision products include a built-in infra-red illuminator that is meant to provide additional light. The additional light makes viewing in the dark a reality.

Types of night vision


A monocular is an NV product that has one eyepiece and one objective. It usually refers to a unit that is held in the hands and is typically between 2x and 5x. An NV monocular has many advantages. It is the smallest NV unit, as well as the least expensive and it offers as much performance as a binocular or goggle. The only disadvantage of a night vision monocular is that it allows you to use only one eye when you observe. Over long observing sessions, this can create eye strain and fatigue, but, fortunately, most NV observing is intermittent, not continuous.


An NV binocular is much the same as a daylight binocular in that it offers two eyepieces and two front lenses with the addition, of course, of an NV intensifier tube. An NV binocular still only uses one intensifier tube system, so it won't offer greater performance or range than a monocular, but it will provide more comfortable viewing since you are you using both eyes. However, an NV binocular will also be heavier and more expensive than an NV monocular.


An NV goggle is any unit that comes with a headset.

Night Vision generation and performance

The generation of an night vision device product will determine many things, principally performance and price. There are several generations of night visions:

Gen 0 Night Vision

The first night vision aids (also called Generation Zero or Gen 0) were sniper scopes that came into use during World War II and the Korean conflict. These were not true image intensifiers, but rather image converters, which required a source of invisible infrared (IR) light mounted on or near the device to illuminate the target area.

Gen 1 Night Vision

This is the least expensive and oldest technology in night vision. All gen 1 intensifier tubes are made in the same factory in the Ukraine, so all Generation 1 Night Vision Devices will have roughly similar performance. (Gen 1+ indicates a current production tube, not a better grade of tube). Only features other than the intensifier tube that affect Gen 1 performance are objective size (large objectives supply more light), magnification (more is NOT better- this is a low resolution product) and the IR illuminator (need by all gen 1 products under tough conditions). If you are using an NV in a marine environment, be sure to use a waterproof model.

Gen units are easily identified. Gen units require 15-30 seconds to power up or power down and will always have some pronounced optical distortion (fish-eye distortion) at the edge of the field.

Gen 1 units can be used to about 75-100 yards to detect man sized objects under average conditions and perhaps a bit more under ideal conditions, say full moonlight. Detection range is defined as the range in which a target will present a recognizable silhouette. Recognition range is defined as the range in which a target begins to show recognizable detail. For most Gen 1 units, this will typically be 50-75 yards or less for a man sized object. It is important to understand that smaller targets will reduce both detection and recognition range.

Gen 2 Night Vision

The biggest gain in performance occurs between Gen 1 and Gen 2. With a gen 2 tube, you get much reduced distortion at the edge of the field, a screen with better contrast and resolution, better light amplification (less reliance on an IR for supplemental light) and improved tube life. This all translates into greater range, for both detection and recognition, typically another 50 to 75 yards on both, depending on the grade and type of tube.

Gen 2 also introduces options for grade and type of intensifier tube, though the designation of Gen 2+ indicates a current production tube, not a higher grade of tube. To check performance on a 2nd Generation Night Vision Device, you need to check for both resolution (lp or lpm) and type of tube. Special XD Gen 2 tubes, HDT Gen 2 tubes and SHD3 Gen 2 tubes approach Gen 3 Night Vision Device in performance, but also in price. They truly do bridge the gap between Gen 2 and Gen 3.

The most common measure of tube performance, and one that should always be checked on Gen 2 tubes and higher tubes, is resolution, stated in line pairs per millimeter (lpm) or sometimes just abbreviated as lp. As resolution goes up, so does price.

Gen 3 Night Vision

This is the highest generation of night vision technology commonly available and the generation currently employed by most military units and other serious users. Generation 3 Night Vision Units, under ideal conditions, are able to detect human sized objects at ranges of two hundred yards or more. As with Gen 2 units, there are many grades and options offered. Gen 3 tubes also offer vastly improved tube life and rarely, if ever, need to be replaced. All Gen 3 units are variations on the original AN PVS-14 (monocular) and AN PVS-7 (bi-ocular goggle) used by the military.

The most common measure of tube performance, and one that should first be checked on a gen 3 units is resolution, stated in line pairs per millimeter (lpm) or sometimes just abbreviated as lp. Other measures used for grading Gen 3 intensifier tubes include signal to noise ratio and screen quality (evenness of brightness and lack of dark spots), though these specifications are seldom listed or stated by manufacturer.

A grading system based on letters is sometimes used as follows for Gen 3. Intensifier tubes designated as Mil-spec must meet minimum military standards for all tube measurements and specifications. Since the origins of NV are military in nature, this is as good as it gets in NV performance. This is also the most expensive and difficult to obtain grade of NV , especially during wartime. Next are tubes that do not meet mil-spec standards. These are typically referred to as commercial grades. A commercial Grade A tube will typically fall short of mil-spec in just one measurement, often with only a minor dark spot on the screen. It may otherwise offer as much resolution as a mil-spec tube. Check the specs. A Grade B commercial tube typically falls short of mil-spec in more than one measurement, though the lower price may make it a good option.

Gen 4 Night Vision

This generation of night vision optics is not commonly seen or produced and was developed as an option for the military, who chose not to adopt it. Generation 4 Night Vision Devices is not as affected by bright light as other generations of NV, but tube life is reduced compared to a Gen 3. Performance is otherwise on a par with the best Gen 3.


Night vision technology is about seeing in the dark; it is not about seeing great distances. Simply put, no night vision product (night vision goggles, night vision binoculars, night vision scope, night vision rifle scope, night vision monocular, night vision goggles) will have the optical resolution of conventional daytime instruments such as binoculars, riflescopes, monoculars and so on. Because of this limit on resolution (screen sharpness), magnification in night vision products is limited, with 5x or 6x being about maximum. The problem, in a nutshell, is that as magnification goes up, image quality in night vision goes down. Excess magnification in this technology degrades the image to the point of being useless. Best image quality in conventional night vision technology is usually obtained at 1x (normal vision, no magnification) to about 3x. Field of view, image steadiness and overall ease of use is also better at these lower magnifications.

Angle or Field of View

The measure of the angle defining the field visible through the Night Vision system is at a distance of 100 yards.

Bright Source or Over-Light Protection

An electronic circuit turns the power to the Night Vision device down or off when it is exposed to bright light (such as automobile headlights). This protects the image intensifier and extends its life. The device will recover and resume normal operation in 1-2 minutes.

Image Intensifier or Intensifier Tube

The active component in a Night Vision System that amplifies light and presents is a usable image.

Infrared (I.R.) Illuminator

IR illuminators were originally designed to offer supplemental light for close up work, such as reading maps and, as such, are limited in their power, despite advertising claims to the contrary. For example a 450 milliwat model offers about half the wattage of a standard penlight flashlight. In a nutshell, an IR will not offer much help beyond 50-75 yards or so, but it will add considerable detail at closer ranges. An IR illuminator is a must for any night vision unit being used in total darkness, for instance, in the confines of a darkened building, where there is no ambient light. All Generation 1 units will need the assistance of an IR for most applications.

Objective Lens

Collects all available light and focuses it on the image intensifier. It also provides image magnification. The best objective lenses have low magnification (5x or less), are high-speed (f2 or faster) and are coated for maximum efficiency in the near-infrared bandwidth.

Phosphor Screen

Positioned at the back of the intensifier tube, the green phosphor screen renders a visible night vision image. The human eye is most sensitive to green contrasts. The image that you see is actually not the physical object itself, but a projected, amplified electronic image on a phosphor screen, which glows with a green colour. So you cannot see other colour with a night vision device.


Converts light (photon energy) into electrons (electrical energy), then amplified in the intensifier. The objective lens focuses available light on the photo-electric surface of the photocathode which is excited and passes electrons within the tube.


A measure of the ability that render and display a detailed image. Image intensifier resolution remains constant and is expressed as the maximum number of line pairs per millimeter (lp/mm) that can be discerned when a black-and-white stripe pattern is focused on the photocathode.

The amount of light gain (15,000 to 40,000 times) produced by the tube determines the brightness and clarity of the viewed image. The higher the quality of the NVD, the bigger the effective range and more brightness of image.

Black spots on image area a given in all night vision devices.

Night vision image tubes are never flawless, and every night vision intensifier tube will have blemishes to some degree. These blemishes translate into scattered black spots on the image area. This is where price comes into the frame. Cheap devices will have more and bigger black spots than the more expensive ones. The fewer and smaller the blemishes, the better the quality and therefore the higher the price.


Another point to remember is the fact that NVD uses batteries. Good batteries will last for up to 8 hours constant use, so one set of batteries will not last if you plan on going on a number of night game rides during your safari/visit to game reserves.