A spotting scope is essentially a telescope that has a shorter focal length. It is designed to be used for spotting terrestrial targets that are outside of the range of binoculars. Spotting scope allows hunters to evaluate and locate game from great distances, thus avoiding detection. Thus, the hunter is able to determine if the animal they see is worth their effort.
How to Pick Your Spotting Scope & Understand It's Features
They are different types of these scopes; they come with variable and fixed focal lengths. Those with variable focal lengths are better for scanning wide fields. The observer can then examine a specific area by zooming in. To manage the huge focal lengths of spotting scopes, a lightweight tripod is usually needed.
If this is your first time purchasing spotting scopes, here are a few important issues you should consider.
Understanding The Fields of View
This can be defined as the widest dimensions of a viewing area that can be observed using the spotting scope. The field of view is measuring in angular degrees or using linear feet at a thousand yards. This site explains this in great detail.
It is important to note that this field decreases as the magnification increases. Thus, it is usually smaller in a spotting scope than in binoculars. In binoculars, this ranges from one to three degrees. At close distances, the field of view is critical. Thus, this range is enough for long distance and medium observation. The least near focus distance is usually at about 30 feet.
The eyepiece design plays a critical role in determining the field of view. Some eyepieces can deliver a wide field of view. These are often used when you need to follow a moving object, especially in wildlife observation. In practice, eyepieces with a variable focal length have narrower field than those with a fixed focal length. Additionally, eyepieces that are designed with long eye relief will usually have a narrow field of view.
What is the Aperture?
The aperture of a spotting scope is usually the diameter of its objective lens. This is normally measured in terms of millimeters. Most scopes will have an aperture of between 50 and 90 mm. The aperture size will usually have a major influence on the size and weight of the entire scope. The optical design and the focal length will also have an effect on the size and weight of the scope.
The size of the aperture will determine how much light the spotting scope can collect. If it can collect more light, it will be able to collect more detail on the image even in low light conditions. The observed image brightness will usually depend on a number of other factors. These are the coating used, the aperture, exit pupil relationship, and the focal length of the objective lens.
How to Choose Your Focuser
Spotting scopes have three different types of focusing mechanisms. A scope can use rack and pinion, helical, or knob focusing. All of them are effective, but the effectiveness will be determined on how you plan to use your scope. Here is an in-depth explanation of different types of focusers.
A Helical focusing mechanism will have a rubberized collar around the scope. This is what is used to change the focus quite rapidly by turning the ring. A helical focus mechanism is great when dealing with fast-moving objects that are far away.
The rack and pinion design are common on telescopes used for astronomy. It usually gives a smooth but fast focusing. However, all of its components are located externally, which makes them subject to degradation from the elements when used in the field.
The third and final focusing mechanism is the knob focus. This mechanism is slow, but it allows for precise focusing. It is quite effective to use in slow moving targets that are great distances away.
Understanding the Different Type of Coatings used
When choosing a spotting scope, ensure that it has high-quality anti-reflection coatings. These will help the equipment perform optimally. It also prevents glare, which can cause the targets to run away. During the Second World War, the best binoculars at the time could only capture about 50% of the light. However, due to the advancement of anti-reflection technology, some of the most advanced lenses can transmit about 98% of all the light they capture.
What is the Focal Length and Why Does it Matter?
The f.l of the spotting scope is the distance between the objective lens and the distance at which the rays of light converge to form a clear image. The eyepiece will also have its focal length. The combination of these two leads to the magnification of the image. The magnification is the Objective lens f.l. divided by the eyepiece f.l. The focal length is often expressed as the focal ratio. The ration is the diameter of the aperture to the f.l. of the objective lens.
Why is Glass Quality Important?
The best quality spotting scopes are made of lenses made from extra-low dispersion glass or fluoride coated high-density glass. The difference in the image quality using high-quality glass and the ordinary glass becomes apparent in low light. The glass quality you choose should depend on the kind of activity you plan to carry out. If you mostly hunt at night, that will mean you will have to acquire high-quality glass lenses. At this site you will find an explanation why glass quality matters.
What is the Purpose of The Eyepiece?
Choosing the right eyepiece is an important aspect of buying a spotting scope. The eyepiece helps to magnify the image and brings this image a certain distance behind the eyepiece. The diameter of the image is what is called the exit pupil. The eye relief is the distance at which it is behind this eyepiece. The magnification of the image is dependent on the focal ratio discussed above.
Eyepieces are varied. Some have a variable focal length while others are fixed. Others will have a wide field of view while others have long eye relief, which is great for those who use glasses. The eyepieces also attach to the spotting scopes through various means. They can be fastened with a setscrew, a bayonet mount, or direct screw threads.
Some of the scopes come with eyepieces that cannot be removed. These spotting scopes are designed to be waterproof or they have variable focal lengths. They eyepiece placement over varies. Some are designed to be viewed at 45 degrees and some at 90 degrees. The diameter also varies from less than an inch to as wide as 2 inches.
The placement of the eyepiece is personal preference. However, most hunters prefer the straight through placement. This design is easy for spotting a moving object. It is especially convenient to use on scopes mounted to vehicle windows.
Under the Different Optical Designs of Spotter Scopes
For spotting scopes, only two types of optical design are used. These are the catadioptric and refractor. The main difference between these two designs is the kind of material used for focusing the image. Catadioptric use mirrors to reflect the light while refractors use glass to bend light to a point of focus. Although this may seem basic, it translates to major distinctive characteristics in their functions.
- Catadioptric Scopes
This design utilizes a combination of a corrector lens and mirrors to focus the image. The system has a long focal length, which is folded using mirrors in a compact tube. These scopes can achieve amazing magnification, and they are quite light. They have a long focal length, combined with a wide aperture of up to 90mm, which can allow for 200X magnification.
Their main drawback is that they have a limited field of view. They can come with a 45 or 90 degree erecting prism, making them undesirable for hunting. Both of these prisms work well to view objects that are above the horizon. To change magnification, eyepieces with fixed focal length are interchanged.
Since these scopes have such a narrow field of view, they are often used with a finder scope to help center the main scope on an object a great distance away.
The design is quite simple. At its most basic, a long tube has a primary lens on one end and an eyepiece on the other end. For those that are used in hunting, they will come with an image-erecting prism in the tube between the two lenses. The prism helps to provide an image, which is correctly oriented as well as in the right position right and left. This YouTube video does a good job of explaining the basics behind this scope.
For a scope used in hunting, the focal length is short to make it easier to carry the spotter scope. The eyepieces used in a refractor scope are interchangeable. Those with a fixed focal length are often attached with a bayonet mount or with screws.
These scopes also come with zoom eyepieces. While working in the field, these provide flexibility, although some resolution, brightness, and the field of view are lost. The most common focusing mechanism used in a helical knob, located internally and thus protected from dust and moisture.
In general, if you want a durable, simple spotter scope that is easy to use and reliable, you should go for a refractor scope. These scopes require almost no maintenance, which is great for those who often hunt in rugged areas. They are quite popular not just for hunting but for most outdoor activities as well.