So the short answer here is, "Yes, you can use a telescope for terrestrial viewing". But there are a couple of points that need to be discussed so that you know what to expect and how to maximize the experience.
Let's begin by taking a look at the basic design of a telescope. And this goes for any telescope in general, not any one particular type.... so refracting, reflecting, and compound. If you want to know about teach of these types of telescopes, be sure to read our companion article on the "Types Of Telescopes". Telescopes are designed to used to gather as much light as possible from the object being viewed. Typically this means viewing sessions at night looking at a distant planet, or moons, nebulas, etc. that are very, very far away. The point here is that the celestial objects being viewed are small, distant, and surround by the vast emptiness of black space. For this reason, telescopes are specifically designed to pull in as much light as possible that is emanating from the object.
Next, let's compare viewing distant objects at night with viewing terrestrial objects (during either night or day). Objects here are planet Earth are relatively close. Five miles away may seem like a long distance, but compared to the deepness of space, it is an infinitesimally small distance. Also, the environment surrounding the object of interest is usually surrounded by other objects, and each of those objects may emitting/reflecting their own light. The other objects may be street lights, traffic lights, office buildings, signs, streets and sidewalks (yes, there is a LOT of light reflecting from the surface of a sidewalk!).
So what does this mean? It means that the telescope is an optical instrument that has been designed and optimized to work in a dark environment to view distant objects (millions of miles away). Using a telescope during the day to watch birds 1/4 mile away is a VERY different situation. As such, you'll need to make some adjustments in order to adapt for the different environment.
Before You Get Started Viewing Object On Land
In general, many (but not all) telescopes made for astronomy will invert the image. Presenting the image upright is important for terrestrial viewing, but it usually doesn't matter for astronomy. How do you correct the inverted image? It will require the use of an "image erecting diagonal prism". You may also see/hear it referred to as "roof prism", "erecting prism", "image prism", "diagonal prism", etc.
The diagonal/prisms will redirect the light so that it is inverted to the correct orientation. The diagonals are constructed as either a mirror mounted at a 45 degree angle, or a prism. An advantage of a prism is that it can reflect light at either 90 degrees or 45 degrees. For astronomy, a mirror is more preferred because it is going to reduce the light loss. In either case, you'll need to purchase an image erecting diagonal prism BEFORE you attempting to view land-based objects (unless you don't mind seeing objects upside-down!).
TIP #1: Get an image erecting diagonal prism
Magnification vs Usability
As mentioned earlier, the objects on land are relatively close when compared to the planets and stars in the night sky. As a result, you'll typically need a lot less magnification to view the land-based objects. In fact, you'll usually get better results when you are using a lower power magnification configuration. You may be wondering why this true, and the answer is quite simple. When you think of magnification, maybe you only think that the image of the object being viewed will be larger. This is true, but have you also considered the fact that the magnification capability of a telescope also amplifies other related aspects as well ? Specifically, we are talking about image quality in terms of usability. For example, any vibration of the telescope, mount or tripod gets amplified and shows up in the eyepiece where the image is being viewed. The vibration can be someone walking by, wind gusts, or even just adjusting the focusing knob.
Here's another reason why using lower power magnification is preferred over higher power. The lower power magnification will have a larger field of view. How does this translate into usability? Well, with a higher magnification it may reduce the field of view so much that tracking a moving land-based object may be difficult if not impossible. To help illustrate this phenomenon, imagine that you are ten feet away from a horse that is walking by as you try to view it through a soda straw. You wouldn't be able to see all of the horse AND you'd constantly be moving the straw around to track the movement of the horse. So how do you avoid this situation? Simply reduce magnification power so that you have a larger field of view.
TIP #2: Use lower magnification power for more usable results
Alternatives To Use Instead Of A Telescope
Is there an alternative to a telescope ? Yes there is an alternative, and it is an optical instrument called "binoculars".
Binoculars, sometime referred to as field glasses, can be thought of as two small telescopes that are mounted side-by-side. You use them by holding the binoculars up to your face and positioning the eyepieces directly in front of your eyes. One unique characteristic and advantage of binoculars is that because you are viewing an object with both eyes simultaneously, the viewed object is seen as a 3D image.
Another advantage of binoculars is that they are purposely designed for viewing terrestrial objects, and the viewed object is optimized for the best results. Including the fact the binoculars have the image erecting capability built into them, there is no need to purchase and install anything extra.
Also, binoculars are made to work with the higher light levels that are present during daytime viewing. The functionality of binoculars work on the same principle as telescopes, but they are crafted to accept the flood of ambient light from the environment as well as reflections form nearby objects.
As for magnifying capability, binoculars are available in many different magnification power configurations. In fact, there are even binoculars that offer an on-the-fly variable zoom capability so that the viewer can instantly change the magnification power configuration while viewing the object. All it takes is a simple press of a lever or rotation of a knob.
Yes, you can use a telescope for terrestrial viewing, but with the features and capabilities available in binoculars today you can think of them as the ideal, purpose-built optical instrument for viewing land objects. If you'd like to know more about binoculars and their ability to be used for astronomy, check out our companion article on "Astronomy Binoculars".
TIP #3: Binoculars are a great alternative instead of using a telescope to view land-based objects
Wrapping It Up
Yes, it is possible to use a telescope for terrestrial viewing of objects. It will require the use of an image erecting diagonal prism and some judicious use of magnification power in order to obtain acceptable results. Keep in mind that during the the daytime, viewing land-based object with a telescope is less than optimal because there is so much ambient light.
Whatever you choose, telescope of binoculars, Enjoy it and make the most of your viewing sessions !