If you’re looking to buy a telescope and are wondering what aperture to choose, you’re not alone. The aperture of a telescope is the diameter of its main objective lens or mirror.
It determines the amount of light that the telescope can gather and thus affects the clarity, brightness, and resolution of the images you’ll see.
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In this article, we’ll delve into aperture’s impact on telescope performance and its best size for various stargazing types.
Contents
What is Aperture and Why is it Important?
The aperture of a telescope is like the entrance of a camera lens – it controls how much light enters the instrument.
The larger the aperture, the more light it can gather, and the brighter and clearer the image will be.
But a larger aperture also means a larger, heavier, and more expensive telescope, choosing the best telescope can be daunting.
Additionally, optics quality and telescope design impact image quality, so a bigger aperture doesn’t guarantee a better telescope.
The aperture is measured in millimeters or inches, depending on the country and the manufacturer.
Amateur telescopes typically range from 50-400mm (2-16″), with reflectors around 100-200mm (4-8″) and refractors at 80-120mm (3-5″) being most common.
Professional observatories can have apertures of several meters (tens of feet).
How Does Aperture Affect a Telescope’s Performance?
The aperture affects several aspects of a telescope’s performance, which we’ll explain briefly:
Brightness: The amount of light the telescope collects determines how bright the image will be.
The human eye can detect stars down to a certain magnitude, which depends on its sensitivity and the conditions of the sky.
With a larger aperture, you can see fainter objects and details, and you can observe under darker skies or in more light-polluted areas.
Resolution: The ability of a telescope to distinguish closely spaced objects or details is called its resolution.
It depends on the wave nature of light, the size of the aperture, and the quality of the optics.
In general, larger apertures yield higher resolution, but they also require better optics and a more stable mount.
The atmospheric turbulence, or “seeing,” limits a telescope’s resolution, causing stars to twinkle and blur.
Contrast: The telescope’s capacity to display subtle differences in brightness or color defines its contrast.
This aspect depends on the optics, the telescope’s design, and the eyepiece or camera’s quality.
Planets require high contrast, while galaxies benefit from low contrast, which showcases delicate structures against a dark background.
Field of view: The size of the sky area visible through the eyepiece is the field of view.
It depends on the focal length of the telescope, the design of the eyepiece, and the size of the sensor or film.
A bigger aperture enables shorter focal lengths and wider eyepieces for a broader view, necessitating precise alignment and focusing.
What Aperture Size is Best for Different Types of Stargazing and Observing?
The best aperture for a telescope depends on several factors, such as your budget, your observing location, your observing targets, and your personal preferences.
Here are some guidelines for different types of stargazing and observing:
Visual observing of planets and the Moon:
For observing the planets, the Moon, and other bright objects in our Solar System, a medium-sized aperture of 80-150mm (3-6 inches) is usually sufficient.
This is because these objects are relatively bright and small, and their details can be seen with high contrast and resolution.
A larger aperture can also be used but may require better conditions and optics to reveal finer details.
Visual observing of deep-sky objects:
For observing galaxies, nebulae, and star clusters, a larger aperture of 150-300mm (6-12 inches) is recommended.
This is because these objects are faint and spread out, and their details require a larger aperture and a wider field of view.
A smaller aperture can also be used but may limit the brightness and resolution of the objects.
Photographic observing of planets and the Moon:
For taking pictures of the planets, the Moon, and other bright objects in our Solar System, a small to medium aperture of 80-150mm (3-6″) is usually sufficient.
This is because the exposure times are short and the images can be stacked to increase the resolution and contrast.
A larger aperture can also be used but may require higher magnifications and faster shutter speeds.
Photographic observing of deep-sky objects:
For taking pictures of galaxies, nebulae, and star clusters, a larger aperture of 150-300mm (6-12″) is recommended.
This is because the exposure times are long and the images need to capture as much light as possible.
A smaller aperture can also be used but may require longer exposure times and may not reveal fainter details.
Conclusion
The best aperture for a telescope depends on your observing goals, your budget, and your preferences.
A larger aperture can generally provide brighter, more detailed, and more impressive views, but it also comes with a higher price, weight, and complexity.
A smaller aperture can still offer rewarding views of the Moon, planets, and bright stars, and can be more portable and affordable.
If you are looking for a detailed breakdown of the top telescopes, then look at our guide on the very best on the market now.
Whatever aperture you choose, opt for a trusted manufacturer, good optics, and an aperture suitable for your experience and site. Enjoy stargazing!
