If you have some prior knowledge on optical instruments, or currently use a telescope or binocular or even a monocular you know and have some understanding on how to use them and this guide will be added information for you to have. This guide is an easy and helpful information tool for you to know and understand more about spotting scopes. For a start, do you know what they are and how they work? The below will help you gain some insight of what they are and the features they consist of. Lets begin!

What is a Spotting Scope?

Much like a telescope, binocular and monocular, it is an optical instrument that allows you to view objects at a distance. It is usually used to observe objects on land. This instrument is quite bigger than a normal binoculars, ranging from 15x to 60x magnification and a 50mm to 80mm objective lens. Of course there are some with even higher than 60x magnification and objective lenses that are 90mm and up!

Lens Coating and the Types

As you now know, the main job of the objective lens is capturing as much light as it can and deliver it to the eyepiece. In order to achieve a more substantial amount of light transmission, the optics are coated with special chemicals. Many of the spotting scopes are coated with a microscopic film of magnesium fluoride. Damaged objective lenses whether it’s a scratch or a chip; will render the optic useless. This makes the objective lenses the most important element of the instrument and coating it allows better light transmission. To get exceptional color correction and sharp images, the best option would be the Extra Low Dispersion Glass. It would allow your instrument to provide you with sharp detailed images especially when bird watching and would eliminate chromatic aberration, which would make astronomical viewing absolutely phenomenal! There are different amounts of layers a lens can be coated with and the highest quality scope would be coated only by the best! The types of coating are the following:

• A Coated lens would indicate that there is a single layer on one lens surface.
• A Fully Coated lens signifies that there is a single layer on all air-to-glass surfaces.
• A Multi-Coated layer implies that there are multiple layers on at least one of the lens surfaces.
• A Fully Multi-Coated lens indicates that there are multiple layers on all air-to-glass surfaces, giving it the possibility to achieve 95% light transmission. What this means is that 95% of the light absorbed by the objective lens will reach the eye.

The more coating there is on an objective lens the better resolution you receive getting the image appear more clearly opposed to a less coated lens.

Exit Pupil

It is the size of the circle of light visible at the eyepiece. The exit pupil is signifies how bright objects will appear in low light conditions. It can be calculated by diving the object lens diameter by the magnification, and the higher the number the brighter the image. For example a 15x45 model would have an exit pupil of 3mm (45 divided by 15 = 3).

Eye Relief

This refers to the distance between your eyes and the instrument while the whole field of view is still visible. Longer focal length of an eyepiece, gives greater eye relief. This is ideal for people who wear eyeglasses and will reduce eyestrain.

Field of View

Is the measurement of area that can be seen through your optic. It is the width of the area, usually in feet, visible at 1000 yards. The field of view can be measured by two the magnification and the eyepiece design. A wide field of view can allow you to see objects better especially when scanning for them or watching birds in their natural environment. An FYI is that the higher the magnification the narrower the field of view.

Close Focus

Is the closest distance your instrument will focus on an object. It is measured in inches rather than yards, and this feature is one to look out for if you are using your instrument for bird recognition or insect inspecting.

Magnification

The magnification is the first number presented in the specifications. The magnification signifies the degree in which the object is enlarged. If the instrument is a 15x60, in this situation the object appears to be 15 times closer to you then when looked at with the naked eye. With a spotting scope you can find many that are ‘variable power’ and they will be represented in a formula that looks like this: 15-45x60. What this means is that the object can appear 15-45 times closer. Of course, when using such high magnification a tripod should be used, as the instrument will be too heavy to hold, especially if trying to view an object steadily.

Objective Lens

The second number that is presented in the formula (45x60) is the aperture. This means that it presents the diameter of the objective lens or the front lens in millimeters; in this case it would be 60mm. This determines the ability your instrument has to gather light. The larger the objective lens the brighter the image.

Folded Light Path

This allows the design to become more compact yet yielding long focal length performance. It is done through the combination of optical configuration to create a total scope length shorter than the one provided by the system by using lenses and mirrors.

Prism Glass

Most instruments use a BK-7 glass or a BAK-4 glass. The BAK-4 glass is a higher quality glass than the BK-7 providing you with brighter and sharper images.