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When using a telescope you will need to understand a little about how the key accessories work as they will impact what you see (eyepieces and barlow lenses) and how easy it is to operate (mounts and tripods).
Below we outline the basics that you need to know about:
- Barlow lenses
1. Telescope eyepieces
Telescope eyepieces attach to your telescope and are what you look through. The differences between different eyepieces determine the magnification and field of view of a telescope.
The magnification of a telescope is determined by dividing the focal length of the telescope by the focal length of the eyepiece.
The field of view is the amount of sky visible through the eyepiece. Using higher magnification eyepieces results in a smaller piece of the sky, and therefore a smaller field of view.
Different eyepieces are used for viewing different objects. For example, some objects, such as nebulae and star clusters, appear quite large and are best viewed at low magnifications (which give a wider field of view), whereas planets appear very small and are normally viewed with high-magnification eyepieces.
A common misconception is that magnification is the most important aspect of a telescope but actually the diameter (aperture) of a telescope determines its power and different eyepieces are used to get the best view of a given object with often the best view at a low magnification.
When buying a telescope it is worth looking at the comments made by other users as to the quality of the eyepieces that come with it as it may be that you’ll need to upgrade these. Doing so can have a great impact on improving what you see and so can be well worth it for a relatively low cost.
The size of the eyepiece refers to the diameter of the tube – and whether or not it will fit on the barrel of your telescope’s focuser. Make sure to check when buying, but the most common one is the 1.25-inch eyepiece which has become industry standard.
2. Barlow lenses
Barlow lenses are optional accessories that sit between your telescope’s focuser and your eyepiece.
They usually double or triple the magnification of any eyepiece (depending on whether they are 2x or 3x etc.) and therefore provide some greater diversity to your viewing options when combined with different eyepieces.
The downside of using a Barlow lens is that they can result in a degradation of the view via a slight blurring and as such are usually not recommended for use with astrophotography.
When selecting a Barlow lens, make sure you choose one with the correct barrel size for the eyepieces you have. As mentioned above, most eyepieces are 1.25 inches these days, but be sure to check.
A finderscope is a small scope mounted on top of your telescope that helps you aim at what you want to view. They have a much wider field of view than a telescope, making finding objects much easier.
Alternatively, a telescope may use a red dot finder. This is also a tool for aiming but has no magnification and works by superimposing the image of a small red dot onto the night sky.
A mount is an instrument that fits between your tripod and telescope and allows you to adjust where the telescope is pointing.
There are two main types of telescope mounts:
Alt-Azimuth mounts are the most common and basic mount. They allow telescopes to be moved in altitude (up and down), or azimuth (side to side), as separate motions.
Equatorial mounts are more sophisticated and work to automatically adjust where your telescope points in tune with the Earth’s rotation. This means that your telescope can follow what it is pointed at even when the earth moves.
Mounts can be motorized which means you do not have to manually turn knobs for the mount to move and track objects. This increases precision and decreases the vibration that occurs when you touch your telescope.
This can also be combined with computer-controlled GoTo technology to automatically locate and track objects from large databases.
A telescope will generally sit on a tripod to enable you to use it when standing (or sitting), similar to a camera tripod.
Look at the length of the tripod that comes with your telescope. Some can be quite short and would require you to stoop quite low. This is especially a problem with refractor telescopes where the eyepiece is located at the lower end.
There are also differences in the sturdiness of quality tripods versus cheaper ones. A good tripod will be strong and will minimize any potential shake coming from the wind.
Some telescopes are tabletop models, which can be perfect for some situations like backyard viewing, but consider where you will be using it and whether you might need to add a tripod to be able to use it in different places.
Telescope tripods need to be heavy duty to be able to hold the weight. Usually, when you buy a telescope it will come with a mount and telescope as a package, but be sure to check.
Telescopes often come with accompanying software. These are usually one of two things:
- If it is a telescope with GoTo functionality, then it will be the database of objects that your telescope will be able to find for you (very useful)
- If your telescope does not have GoTo functionality, it is likely to be some educational resources which will probably not be essential to you although may be nice to have.