What is the difference between telescope lenses

Different spectrum of colors focuses on different focal planes which result in the image having a shifted color tint. In comatic aberration, all the rays focus on the same plane but they are stretched out and does not focus on a single point. It results in the star looking like a comet with a tail. It is the combination of chromatic and comatic aberration COMA , where the different wavelengths meet at different points on the same focal plane. Ghosting is the faint appearance of the secondary image of the stars or any other bright object in the sky.

It is the distance from the last lens of the eyepiece where the image forms. Ideally, you want a longer eye relief which can really help if you wear glasses.

Eyepieces with basic designs have very short eye relief. How wide of a view can you see through a telescope is what we call the apparent field of view. The eyepieces play a big role in giving a wider view. The wider view gives you a more immersive viewing experience. The field of view is measured in angles or sometimes radian.

Eyepieces can be divided into three categories on the basis of their apparent field of view. Click here for more info on optical aberrations opens in new tab. Saving costs is the main reason why telescopes come with just a basic eyepiece. Unlike the main mirror and lens — an eyepiece is one of the most replaceable interchangeable parts of the telescope which can be easily swapped. Saving a few bucks on the eyepiece allows the manufacturers to use better materials for the more important components like the main mirror or the lens.

Which cannot be upgraded later and you are left with what you get out of the box. There are way too many advantages of upgrading your eyepiece, it steps up the performance of the whole telescope and does not cost much in most cases. So after you had your initial look from your telescope you should upgrade them.

A telescope comes with two sets of eyepieces. One of them usually have a smaller focal length of around 10mm and the other one is the mm eyepiece. Ideally, you want to upgrade both of them but if you have to choose the one you should consider upgrading the smaller 10mm eyepiece. The mm eyepiece has lower zooming power and overall they are not that demanding.

Upgrading your eyepieces could be tricky. You may find the eyepieces which come with your telescope are not that bad and you may not feel the need to upgrade them. In that situation, you should go with a different focal range. For example, if your telescope comes with 10 and 25 mm eyepiece you can go with a mm eyepiece.

It will give you a new range to play with and you can also get the performance of 9mm eyepiece using a Barlow. The answer is very simple; light follows the same path no matter which way it's going! To illustrate this on the diagram above, all you'd need to do is draw upward-pointing arrows at the other end of each light ray.

To create a lens which can focus many parallel rays of light to a single point, the idea is to curve the surface of the glass so that all these rays, after passing through, come together at the same place. It's a bit tricky to do this right, but we don't need to worry about the details. Below is a diagram showing how such a lens focuses light. The optical axis of the lens is the thick line which passes right through the middle of the lens; a ray of light traveling along the optical axis is not bent at all.

Rays which pass through the top of the lens are bent downward, while rays which pass through the bottom of the lens are bent upward. Thus all these light rays are bent toward the optical axis. If the lens is well-made, all rays meet at the same focal point. The distance between the lens and the focal point, measured along the optical axis, is called the focal length. A simple lens in operation. Parallel light rays come from the right, pass through the lens, and meet at the focal point on the left.

The thick line through the middle of the lens is the optical axis ; the distance F is the focal length. A lens which could only focus light rays striking the glass head-on as in the illustration above would be fairly useless for astronomy. Fortunately, most lenses can also accept rays which come in at a slight angle to the optical axis, and bring them to a focus as well.

This focal point is not the same as the focal point for rays which are parallel to the optical axis; depending on the angle of the incoming rays, their focus lies on one side or the other of the optical axis, as shown in the diagram below.

But if the lens is well-made, all these focal points will lie on a plane which is parallel to the face of the lens; this is called the focal plane. A simple lens forming an image. The red rays arrive with an downward slant, and come to a focus below the optical axis, while the blue rays arrive with a upward slant, and come to a focus above the optical axis.

The vertical dotted line at left represents the focal plane. There's one slightly subtle consequence of this image-formation process: the image is upside-down! The next diagram shows why: rays from the lower part of the subject on the right come together at the upper part of the image left , and vice versa.

This is also true of any camera you may own; of course, you turn the prints right way up when you get them from the photo store, so you're probably not aware of the orientation of the image inside your camera. The image formed by a simple lens is upside-down with respect to the subject. Here the subject right is an arrow with a red tip pointing upward; its image left, at the focal plane points down. Your simple telescope kit includes a large objective lens which you will use to study image formation.

Take the large lens and mount it at one end of the larger cardboard tube; slide the smaller tube into the other end of the larger one, and use a rubber band to hold a sheet of tracing paper over the open end of the smaller tube.

Ideally it should be close to the size of your dark-adapted pupil — around 5mm to 7mm. This tells you how far your eye must be from the eyepiece in order to see the entire field of view.

A bigger distance called longer eye relief is useful if you wear glasses. This is sometimes abbreviated to FOV, and is the figure that lets you know how much of the sky you can see through your eyepiece.

This measurement is given in degrees. Calculate an FOV before you buy with our field of view calculator. This is just another name for magnification. A telescope just captures the light — it is the eyepiece that magnifies the image.

A telescope collects light. Do they work? Read our full Ultraflat eyepieces review. Get to know your telescope stats, as they will fare you well when selecting an eyepiece.

A good selection of eyepieces will serve you well and give you options depending on what you want to observe. A basic understanding of how the human eye works helps explain the function of eyepieces So, what you need is a selection of eyepieces to match each of your different observing objectives. The Vixen SSW eyepieces incorporate a fully multicoated, seven-element design. Read our f ull Vixen SSW review. A coated eyepiece lens. Image Credit: The Secret Studio. Our rotating eyepiece turret can hold up to four of your favourite eyepieces.

Find out how to build your own with our design at the link below. Credit: Mark Parrish. Buying the right adaptor may enable you to attach your smartphone camera to your telescope via the eyepiece.

Pictured here is the Tele Vue FoneMate Smart Phone Eyepiece Adapter, one of our recommended gadgets to turn your smartphone into an astrophotography camera.