Spotting Scopes: What do you need to look at?
What is a Spotting Scope?
This sort of optical device is essentially a compact, yet powerful telescope. Galileo Galilei would have loved to have something like this instead of his earliest designs. Spotting scopes are designated by three numbers, such as 15-45x, 60. The first two are the zoom range, such as 20-60x, followed by the diameter of the objective lens in millimeters, which is the farthest lens from the eye, and closest to the “object” being viewed.
This last number, such as 30, 50, or 60, directly affects how bright an image will be, so those designed to be used in dim conditions will have a large objective lens to collect the most light. This will also affect the level of detail that is obtained at higher magnifications.
The “x” numbers refer to the amount of magnification available. The pre-Galileo scopes were for navigation, offering a magnification of up to 3-power (3x), which made an image appear to be three times closer than seen with the naked eye.
These were often life-and-death tools essential for spotting land on the horizon, since finding a small island usually meant a place to replenish drinking water, and a chance to catch small game for fresh food. In the case of pirates and privateers, spotting a foreign flag, and how deeply a ship sat in the water, was important because a low-riding ship was usually full of goodies to steal.
Galileo built a 7x scope and eventually worked his way up to a 20x model that was considered something of a miracle. When glass was typically no better than the low quality, greenish-tinted Coke bottles from the 1920-60s, with no particular clarity, often full of micro-bubbles, and lacking vision-enhancing coatings, you would have to be extraordinarily lucky to obtain a piece that would make even a usable lens, let alone a good one. He probably sorted through hundreds or thousands of glass globs to find what he needed.
What do you want to see?
What is your target or objective? Objects of interest can range from birds, airplanes, or ships, all the way up to the Moon itself. With such targets, you might begin by using binoculars, which are essentially a pair of telescopes connected together.
Binoculars, however, are (by necessity) relatively low powered, in the range of 7x to 12x, and even then can be difficult to hold steady. If the magnification exceeds 12x, just holding them still enough to observe relevant details becomes a near impossibility. People tried adding tripods to them, and that helped, but what was needed was a tool halfway between a telescope and a binocular—and the spotting scope was born!
Better than Binoculars; Handier than Telescopes
Telescopes are not very useful for terrestrial viewing. They invert images and swap them left-to-right. This is not a concern for looking at Saturn or distant stellar phenomena which you have never seen in person, and would never recognize as being upside-down. It simply doesn’t matter.
Back here on Earth, however, most of us recognize that robins don’t hang from the bottom of branches. For those of us studying airplanes or sea-going vessels, reading registration numbers upside-down and backwards can lead to inaccurately recording the information seen.
Even Moon enthusiasts might be disconcerted to find the Sea of Tranquility on the left, and the Sea of Rains on the bottom right… and every adjustment moving in a direction opposite to how you adjust the view. Some telescopes can be corrected to be "normal," and others cannot.
These see the world properly. Binoculars are very intuitive to use—point and focus. They always have erect images. As mentioned, however, they are impractical for high magnification. Is that a blue-footed booby doing its amazing mating dance on shore? If only I had a spotting scope…
The Better Way
Spotting scopes and binoculars use a combination of lenses to arrive at an upright, proper image. Sometimes they use prisms, which are just as effective. The biggest (literally) difference is that binoculars are fixed magnification, but spotting scopes can z-o-o-m! Generally, they can manage about four times the highest magnification of binoculars.
Many binoculars are ruggedized and resistant to water penetration; however, when you change the length of the focusing tube, air and atmospheric moisture can move in and out to equalize the pressure. That means lenses can fog up and get dirty.
Except for the cheapest models, spotting scopes eliminate this problem by having the entire focusing mechanism contained within the spotting scope. There are no moving parts on the outside, which allows the inside of the spotting scope to be pressurized to prevent water penetration, even if you drop it in the river.
The advantage extends to having a very powerful focusing mechanism internally, which requires only a 1-2 cm (one inch) movement, instead of several times that for an external mechanism.
If you need an even shorter, more compact model for getting through close brush and tight spaces, there is a catadioptric type available, which, although it is reversed from right-to-left, still gives an upright image. The difference being that a scope with a 90 cm focal length can fit in the size of a 60 cm focal length scope. If you don’t mind backwards text, you can get more power in a smaller package.
Most people wear eye protection in thick brush; many people wear eyeglasses simply for better vision. Hardly anyone crams their eye right up tight against the eyepiece. Having the ability to still see the full image while your eye is farther back from the eyepiece means that you don’t have to remove glasses. The distance your eye can be from the lens, but that still allows you to see the full image, is called the Eye Relief. Make sure it is adequate and suits you. If two people are sharing a single scope, and one wears prescription glasses, having appropriate eye relief means it eliminates refocusing each time.
Not Just for Direct Viewing
Hooking a camera up to binoculars is remarkably tricky. Toting around a telescope for that capability seems like overkill. Spotting scopes can connect to most cameras, but better yet, they can accommodate your iPhone, Android, or just about any smartphone model, too.
A simple holder like this takes advantage of the Eye Relief so that your high-quality phone camera can record images in 1080p or 4K HD without the necessity of bringing along a camera, too.
It's a handy feature when your spotting scope has a close-focus ability. Being able to focus as closely as 5 m (~15 feet), if you’re using your spotting scope to uncover photography opportunities, means that close targets are not out of focus.
Straight vs. Angled
Hunters favor straight spotting scopes. Their targets are generally on a relatively flat plane within their line of sight.
Angled spotting scopes are better for birders (ornithologists) because the 45° tilt of the objective lens means that they don't have to continually crane their neck towards the treetops, which can result in significant muscle strain and pain.
If the objective tube of an angled scope is horizontal, looking down into the eyepiece is easier. We’re much more used to looking down, say at a dinner plate, smartphone, or book, than up at things above us.
Better Lenses and Coatings = $$$
There are different grades of optical glass, from the least expensive Chinese imports to those manufactured in laboratory clean rooms. Even perfect lenses benefit from additional coatings or multi-coats. The more labor and technology that goes into the manufacture, the more you are going to pay. Be practical, however, and only buy what you need. Consult with the retailer for recommendations, or others in your hobby groups, and even try out their equipment if the opportunity arises.
Spotting scopes fill a very particular niche in the optical instrument realm. Powerful telescopes may be too much for the Moon, for example, but a spotting scope can be just right, especially since we're familiar with its appearance, and the image is not reversed in any way. People that engage in target shooting at outdoor gun ranges often employ them to gauge their accuracy without having to walk the length of the range to inspect their targets.
While such scopes can be mounted on solid fixed mounts, they can also be fitted to mini-mounts that are just a few inches tall, or even to ordinary camera tripods. They also have the advantage (at least with the straight models) of being handheld at low magnification, which can be useful if you’re tracking game, or following a birdsong to locate a nest or specimen of your favorite breed.
When telescopes are too much, but binoculars aren’t quite enough, consider a spotting scope—it’s designed to fill that gap!