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Buyer's Guide - Spotting Scopes

Spotting scopes are small, portable telescopes used primarily for observation on land rather than astronomical observation although they can be used for limited astronomical observation if required. They are ideally suited for activities such as long distance bird watching, nature study, telephotography, scenic observation, beginners’ astronomy, surveillance, hunting and long distance microscopy.

Spotting scopes prevail over telescopes and binoculars in certain outdoor situations as they sit in the middle-ground; they provide a clearer image and more magnification than binoculars, and provide the robustness and light-gathering capability that telescopes don’t offer, an obvious advantage in the field, as well as practicality and the light-gathering technology for use in different light conditions that telescopes don’t possess.

Telescopes are also designed with a shorter focal length for lower magnifications and wider fields of view, as well as containing some type of erecting prism to ensure a correctly orientated view is delivered to the user; all of which proves unnecessary for the functions of most spotting scopes.

Type/Design:

The most common spotting scope design is the prismatic refractor, as also used in binoculars; this produces an image the right side up and one correct left to right. The design of the prismatic refractor means it is rugged therefore can stand the vigour of use in the field. Other designs include Newtonian and catadioptric designs, but almost all scopes sold for standard uses, most commonly hunting and birding, are refractive, few are catadioptric and the only Newtonian scope is difficult to find. The main reasons refractive scopes are used over catadioptric designs are the cost and fragility factors of the catadioptric version. Therefore, from this point forward I will refer only to refractive scopes.

There are two main designs for refractive scopes, angled (45 degrees) and straight, both with their advantages and disadvantages.

Using a straight scope, it is relatively easy to locate a subject aligning the eye along the scopes’ body; it is also easier to view a subject from a hidden position such as behind a fence or out of a car. Other advantages of straight scopes include less strain on your neck, less chance of the eyepiece collecting dust/rain and the ease of aiming (especially when inexperienced). Disadvantages include the inconvenience of having to set the eye-level to that of the shortest person if in a group, being the main flaw of the design, this is where the angled scope is often used.

The angled scope provides a means of being able to share a scope within a group without having to constantly change the eye-level of the scope (if mounted on a tripod). It enables a shorter/lighter tripod to be used, but does take getting used to, and can prove awkward to use with a shoulder stock/window mount or with a camera attached. The design of the angled scope makes viewing birds flying or in high positions easier as you do not have to strain; and objects can be viewed from a relaxed sitting position if preferred. If you are likely to be in a group or are likely to be seated, an angled scope is recommended.

Eye-pieces and magnification:

Spotting scopes’ magnification generally varies between 15x and 250x. This means by how many times the image will appear larger/closer through the scope than if it were observed without optical enhancement (i.e. through the unaided eye). The power or magnification of the scope is determined by the eyepiece. These come in different formats; they can be either removable or non-removable, fixed or zoom. Removable eyepieces give a choice of zoom or fixed magnification and can usually be quickly interchanged for practicality and maximum efficiency; the most common types of fixed magnification eyepieces being 20x, 25x and 30x. Zoom eyepieces have variable magnification and can be adjusted by hand within their set range for example 18-36x magnification.

Nowadays with the development of zoom technology, zoom scopes are preferred by most, as objects can be located at low magnification easily then zoomed in on to the desired magnification (for this reason some models come equip with an external peep hole for ease of acquiring the intended image before looking through the high-powered lens). However, the same function can be performed using interchangeable eye-pieces and many people prefer the simplicity of fixed-magnification eyepieces. Previous problems with zoom lenses meant images became too dark as magnification reached 60x but this problem is no longer an issue concerning most products, however low-range products may experience minor issues. If you are going to be viewing the same spot for long periods zoom is unnecessary.

Wide-angled eyepieces are often preferable to zoom lens due to the wider field of view and are often used by people who will be viewing quick moving objects.

When choosing an eyepiece, if you wear glasses you also need to consider eye-relief as some models are more-suited towards glasses wearers. Eye-relief refers to the distance between the eye lens and the point at which the pupil is positioned to obtain a full field of view; this varies between eyepieces. If you do wear glasses you must check the eye relief is within the right distance in order to see the full image.

Lens diameter:

The large, front lens is known as the objective lens. The objective lens diameter, known as the scope’s ‘aperture’, will be given in the specification in ‘mm’. Larger lenses gather more light and produce brighter images; as a consequence they tend to be larger and heavier. The diameter commonly ranges between 50-80mm. When deciding on the objective lens size for your scope you should choose the biggest you are willing to carry, taking into consideration size and weight; with a larger lens you will be rewarded with a superior image (with all other parameters remaining the same).

Lens Coating:

Chemical coatings are often applied to the surface of lenses to reduce the amount of glare and maximise available light. There are a few options available: coated (a single layer is applied to at least one lens surface), fully-coated (a single layer is applied to all air-glass surfaces), multi-coated (multiple layers are applied to at least one lens surface) and fully multi-coated (multiple layers are applied to all air-glass surfaces). The more layers applied the more expensive the scope but the better the image. High-end products will almost always be multi-coated.

Glass:

The better scopes have objective lenses produced from special types of glass to enhance image colour, sharpness and contrast. These types of glass include ED glass (Extra-low dispersion), HD (High Density) or FL (Fluorite) glass. These types of glass make it possible for the scope to focus all the light at (apochromatic) or very near (achromatic) the same point. These glasses, as mentioned, increase detail and reduce strain on the eye. Most scopes are available in the 3 options; these scopes generally cost up to 50% more but are worth the extra cost, few experienced users would argue the improved versions aren’t the extra money. If not using a scope of above 30x magnification you will benefit less from HD/ED/FL glass. If you are planning to view at high magnification or to use your scope for photography then the improved glass is highly recommended.

Focusing:

There are 3 types of focusing method used on refractive scopes. Single-knob mechanism, double-knob mechanism or a helical system. The single knob is the most common, usually located on the top or side of the scope near the eyepiece, focusing is generally quite slow but arguably more precise than using other mechanisms. A Double-knob system is used on Leica scopes and consists of 2 knobs connected to the same mechanism with different drive ratios. The fast knob allows for quick focusing when the slow one can be used for maximum precision when close to optimum focus. Helical focus, used on Swarovski and Canon models, consists of a collar around the body of the scope, good for changing the focus very quickly.

When choosing the type of focusing it is all down to personal preference. Neither method is ‘better’ than the other.

Photography using spotting scopes:

Most scopes can either be attached to a 35mm SLR camera and used as a telephoto lens or connected to a digital camera. Using a SLR, the eyepiece is removed from the scope and replaced by a photo adapter (manufacturer specific to the spotting scope). This contains a lens specifically designed for photography. The camera is attached to the adapter using a ‘T-Ring Adapter/T-Mount’ (specific to the camera manufacturer). Generally; photo-adapters turn a spotting scope into an 800mm F11 lens. A stable tripod is needed and a high quality scope recommended. You will not be able to use the auto-focus setting on the camera due to the scope not having an auto-focus lens so you will have to focus the image manually.

This method of photography is a cheaper way to obtain a 800mm lens for occasional use than having an actual 800mm camera lens.

The advantages of using a digital camera, connected to the lens, to take photos (known as digiscoping), has its benefits. Processing is much easier, the camera is smaller due to no requirement of film and you get instant feedback of the quality of photos. The only obvious benefit of using film is the lower battery requirements.

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Spotting Scopes