Telescopes with low focal ratios (f/4 to f/6) are lower in magnification for their aperture, provide wider fields of view, are favoured for astrophotography, and are more susceptible to showing certain forms of optical distortions. The focal ratios of telescopes usually range from f/4 to f/14. It can be obtained by dividing the focal length by the aperture. Focal Ratio (F-Ratio or F-Number)įocal ratio is a number that denotes the relationship between the aperture and focal length of a telescope. Using a telescope with magnifications also result in a narrow field of view, or being able to see less of the sky. High magnifications are limited by atmospheric conditions during viewing and the telescope’s ability to resolve images, i.e. While it is tempting to magnify as much as possible, a high magnification is not always desirable or possible. The magnification of a telescope can be calculated by dividing the focal length of the telescope by the focal length of the eyepiece being used:įor example, using a 25mm eyepiece in a telescope with a focal length of 1200mm would give a magnification of 48 times. A telescope’s focal length is important in that it determines by what factor your telescope magnifies. While longer focal lengths generally result in longer telescopes, it isn’t always the case as some types of telescopes can manipulate the path of light. Focal Lengthįocal length is the distance between the primary lens or mirror and the point at which the image of the object is in focus. So a large aperture is desirable but extra-large aperture telescopes can be very bulky and heavy, not to mention potentially very expensive. A larger aperture allows the telescope to capture more light, resulting in a brighter and clearer image that is capable of resolving dimmer objects and finer details compared to a telescope of smaller aperture. This is determined by the size of the primary lens or the mirror in your telescope (more on that later). Aperture measures the amount of light that a telescope is able to gather the larger the aperture the more light that enters the telescope. ApertureĪ telescope’s aperture is arguably the most important specification (and it surprisingly has no direct relationship with a telescope’s magnification!). Knowing these terms and what they mean will help you to interpret information present on a telescope. The following are some of the specifications that are present on all telescopes. This article will help you sort out the important bits of information about telescope and help make an informed decision whether you are looking for a telescope for a child or beginner or a telescope for a specialised task such as planetary viewing or astrophotography. You are sure you want to buy a telescope (if you’re not, why not have a quick read here for the differences between some optical instruments?), and you’re possibly ready to dip your toes in, or jump right into, the deep and wonderful waters of astronomy, but which telescope is the right one for you? There are few decisions in life that are capable of seriously changing your life, we believe purchasing a telescope is one of them: a bad purchase can plague your experiences with astronomy forever or a good one can introduce you to a rewarding, lifelong hobby. Looking to buy a new telescope? Read our guide to the different types of telescopes to see what telescope would suit you, whether it's your first telescope or your next upgrade.','different-types-of-telescopes','Which Telescope is Right for Me?'
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