What Does Aperture Mean For Telescopes? Simple Explanation

Primary aperture, aperture size, aperture diameter, aperture power, these terms, and more appear in astronomy and photography conversation all the time. With so many people talking about aperture, it must be pretty important, right?

In fact, the aperture is extremely important when determining how powerful a telescope is and what kind of use it is going to offer to the user.

The dictionary definition for aperture reads:

Noun an opening, hole, or gap especially one in which light travels through

Pretty simple, so what does it mean for the field of telescopes and photography?

In short, the aperture of the telescope is the opening that is pointed towards the object you want to view. It is the large opening on the end which lets in the light, which in turn leads to the magnification and imaging of the object in focus.

Aperture Is Everything

To put it simply, the aperture of the telescope is the most important feature when it comes to magnification and image quality, the two things that people look for the most in telescopes.

The bigger the aperture, the more light it can let in and the better the images become. Every telescope has an aperture whether it is a bargain bin telescope off a drugstore endcap or the Hubble Space telescope. They vary wildly in size but their function is always the same.

The aperture allows light to pass through the inner workings of the telescope to produce the images we know and love so much. Without an aperture, you would get no light flowing through the device and therefore, no images.

Eyepieces, mirrors, baffles, scopes, these are all additions to the telescope that are used to focus and direct let in by the aperture but the light, and the aperture that lets it in, are the most crucial parts of the telescope as a whole.

In fact, aperture size determines a whole lot about a telescope, and knowing the size of the primary aperture can immediately clue you into the power of a telescope in one glance.

Bigger Is Better

One of the only differences between the telescope in your living room and the ones orbiting the Earth is the size of their apertures. The Hubble Space Telescope, for instance, has a primary mirror that measures over 94” in diameter and a corresponding aperture. The average home telescope has a primary aperture measuring around 4” in diameter.

The larger the opening, the more light can be let in. More light means more distant light and fainter light can be processed which allows telescopes to see farther into the universe. Generally speaking, the larger the aperture, the farther a telescope can see by picking up fainter and fainter objects.

Pay attention to the aperture size of the telescopes you are looking at. Most aperture sizes for hobby scopes aimed at casual users will be given in millimeters. Most apertures are going to run between 70mm and 130mm and the larger the aperture is, the larger the telescope becomes.

Primary Aperture? Are There Secondary Apertures?

Most specifications will list the size of the primary aperture. This gives the impression that there is more than one aperture per telescope. This is usually not the case.

Large professional telescopes might have multiple apertures for different instruments or views. Going back to the Hubble Space Telescope, it has a variety of different apertures that each fit a different kind of scientific instrument leading to multiple apertures present on the telescope.

In the case of multiple apertures, the primary aperture is generally the largest one that takes in most of the light for the scope at any given time.

The vast majority of casual telescopes that can be purchased from this website will only include a single aperture. For all intents and purposes, the primary aperture is the only aperture that matters.

To recap, the aperture is the main opening in which a telescope lets light in which allows your scope to focus and magnify distant images. The larger the aperture, the more powerful the telescope. Knowing the aperture size of a telescope can quickly give you an idea of how big and how powerful a telescope is.

Therefore, apertures and their sizes, are extremely important to knowing and understanding telescopes.