Spotting Scopes vs. Telescopes for Astronomical Observing

Since spotting scopes seem to fill an apparent gap between binoculars and large astronomical telescopes, can they make viable alternatives to regular astronomical telescopes, especially in light of the fact that spotting scopes are essentially small, compact refracting telescopes that do not deliver upside-down images? The answers to this question are both yes, and no, and much of either answer depends on the intended use of the spotting scope, as well as the observer’s expectations. Let us look at some of the issues-

Why buy a spotting scope?

Spotting scopes are designed primarily for observing terrestrial targets that are at most a few hundred feet away, such as birds, hornet’s nests, and sometimes the names of ships a little way out to sea, while astronomical telescopes are by definition, intended to be used for observing celestial objects. However, this is not to say that spotting scopes cannot be used for stargazing- far from it. In fact, many astronomers routinely use spotting scopes to observe the heavens, but if you are new to the hobby of stargazing, and have other, ground-based interests as well, there are some important considerations to keep in mind before you purchase a spotting scope for astronomical observations, such as-

Ease of use

“Ease of use” refers to both the fact that even the biggest spotting scope is smaller and lighter than almost any small astronomical telescope, and that any spotting scope is easier to set up and use than almost any astronomical telescope, with the possible exception of small Dobsonian reflectors.

Image credit: Eurooptic

Image credit: Eurooptic

In the first instance, high quality spotting scopes often come with dedicated carry-case that is smaller than most brief cases, as shown in the image above. Therefore, their compactness makes them ultra portable, which means you can take it anywhere, even if you use a spotting scope with a collapsible astronomical-standard tripod.

Image credit: Optics Den

Image credit: Optics Den

In the second instance, there is no complicated setting-up procedure with a spotting scope; you simply attach the scope to the tripod, and you are ready to start observing. This a great advantage over conventional telescopes, especially for novice observers who often experience difficulty in getting the polar alignment right on tracking telescopes.

Spotting scopes (can) deliver great views

Of course, how great the views are depends largely on the quality of the spotting scopes’ optics in general, and the quality of the erecting prisms in particular. Erecting prisms are optical elements that turn images upright, but the problem with many of these prisms is that much of the light that passes through them is often absorbed, or scattered by the prisms themselves. This undesirable trait is the main reason why conventional telescopes mostly do not use prisms, except in cases where the viewing angle becomes a consideration.

Image credit: Optics Planet

Image credit: Optics Planet

Nonetheless, prisms are required in spotting scopes to keep the image the observer sees consistent with what is actually happening on the ground, so to speak. While high-end spotting scopes generally have excellent optics (including the prisms) this is not always the case with budget instruments. In practice, this means that some astronomical images can be degraded by poor optics, meaning that the price of a spotting scope is often directly related to the quality of the astronomical images it delivers. To put this into perspective, consider the image of the Moon above taken through a smart phone with an 80mm Celestron Ultima 80 spotting scope.

As a rule though, a high-end spotting scope with an aperture of 70-80mm will deliver great views of star clusters, double stars (Albireo with its high colour contrast comes to mind), the inner planets, the Moon, and even some bright nebulae, such as for instance, the Orion Nebula. However, as with all small telescopes, faint objects can be difficult if not impossible to spot with a spotting scope, because of all small instruments’ limited light-gathering ability.

Many spotting scopes accept astronomical eyepieces and cameras

While many spotting scopes come with a zoom-able eyepiece, the added optical elements in these eyepieces often make them unsuitable for astronomical observations. The good news is however that many manufacturers of spotting scopes also supply single-magnification eyepieces that usually range between 20×, and 60×, which is the magnification range that many observers with conventional astronomical telescopes use to view some of the objects listed above.

Image credit:

Image credit:

Moreover, many spotting scopes accept adapters with which to fit digital cameras and even smart phones directly onto the scope for basic level astrophotography and digiscoping. However, it must be noted that astrophotography requires a telescope with the ability to track objects to get the best results.

Spotting scopes are (sometimes) cheaper than conventional ‘scopes’

Of course, this depends on many factors, such as the design of the astronomical instrument, the intended use of the spotting scope, the amount of money you want to spend on a telescope, and many others, such as where you want to observe the sky with a spotting scope.

It must be remembered that the lion’s share of the price of a conventional telescope goes toward the quality of the optics, with the remainder accounted for by the cost of the tripod and the tube. By way of contrast, much of the price of spotting scope goes toward making it rugged and waterproof, while keeping the overall weight down. The trade-off is often that the quality of the optics suffers.

In practice, this means that a spotting scope that incorporates advanced features such as low dispersion glass in the optics, fully multi-coated lenses, phase-corrected prisms, and interchangeable eyepieces can be more expensive than a larger astronomical instrument that will likely provide better views because it gathers more light.

However, the trick in buying the right spotting scope lies in not comparing apples with oranges. For instance, when comparing an 80mm spotting scope with an 80mm refracting astronomical telescope, it must be remembered that if the astronomical instrument provides better views, it is not because it gathers more light (both instruments have the same aperture), but because it has fewer optical elements than the spotting scope. In this case, and assuming you have interests other than stargazing, the 80mm spotting scope might be the better deal, simply because it can be used for terrestrial observing as well, where the quality of the optics is not as important.

When reflecting telescopes with apertures larger than 8mm enter the picture, the comparison becomes invalid. Spotting scopes are simply not intended for, or designed to compete with larger reflecting telescopes, which means that if your primary interest is astronomical observing, you can buy a good-to-excellent reflector for the price of an average-to-middling quality spotting scope.

How much do spotting scopes cost?

While price comparisons fall outside the scope of this article, it must be remembered that as with all optical instruments, the price of any instrument is directly proportional to its quality. Thus, in terms of price, a good starting point would be around £300 – £350, which amount will give you a good, solid scope that will provide years of excellent service.

Prices on the other end of the scale can easily run to £2000 or more, which can be too steep for most people. However, as with anything else in life there comes point of diminishing returns, and in the world of telescopes, this means that the small improvements made to average, or even good instruments are often not worth the higher price.

This is especially true of spotting scopes, whose inherent light-gathering limits cannot be improved beyond certain accepted standards- standards that are defined by any spotting scopes’ primary function, which is to view terrestrial targets. Nonetheless, more information on current prices and specifications of spotting scopes for sale in the UK are available online.

Spotting scopes are great for children

One of the main advantages spotting scopes have over conventional telescopes is the fact that they make great, affordable first telescopes for children. The comfortable viewing angle, combined with the fact that images are delivered “right-side-up”, means that children often learn the sky faster than they would normally have done using a conventional instrument that delivers upside-down, or mirror-reversed images.

Image credit: Optics Planet

Image credit: Optics Planet

The mental gymnastics required to match a star chart to an “upside-down” sky often discourages newcomers to the hobby of stargazing, which problem is eliminated with a spotting scope. Children are often not much interested in completing Messier marathons; all they want is a reasonable view of say, the Moon or the Pleiades, and if a good spotting scope can give a child that view, that child will probably remain a stargazer for life. This, when all things are considered, makes a good-quality spotting scope (irrespective of its design) an effective, affordable astronomical telescope.