Choosing A Basic Telescope

So, you have decided you might be interested in Astronomy as a hobby. I am happy to introduce you to the reflector telescope, and explain why a person might choose to buy this type of telescope. Additionally, my intention is to encourage you to consider this as an investment in a fine hobby you can share with your family. Children are awed by the idea of space, everything about it draws their wonder and curiosity. When they are able to view it through a telescope and spend time with you learning and interacting, they tend to remember it for the rest of their lives.

Astronomy is a great hobby, it can become a wonderful tool for you and the family to enjoy with each other and friends. Astronomy does not have to be expensive either. Simply choosing a good starter telescope and the proper accessories is not hard to understand. You should come away from this article with a pretty good knowledge of realistic needs and cost options.

We will look at telescopes in the price range of $200.00 to $400.00. I will present a very basic option as well as an intermediate choice for you to consider. Choices that will be affordable yet offer you quality viewing in return. Additionally, I will suggest learning aids for you that will help you become comfortable with the hobby of Astronomy, and be able to teach your children the simple near earth objects and how to find them.

Click Here: Quality Telescopes And Mounts

THE NEWTONIAN REFLECTOR TELESCOPE:

Reflector telescopes get their name from the fact that their primary mirror collects light at the rear of the optical tube. That collected light is reflected forward onto a small mirror set at an angle (diagonal) which reflects the light 90° into a secondary lens located at the front outer-side of the tube. It is the primary and diagonal mirror acts of collecting and reflecting the light that give these telescopes their name.

Reflector telescopes have a better ability to collect available light from the heavenly objects you seek to view. This is because they have a mirror whose surface has been ground to make it concave. That means it is ground to where the front surface progressively falls below the edge towards the center of the mirror. The mirror is silvered on the back of the disc with an aluminum coating which gives it the ability to reflect. It is the ability to collect light from the edge of the disc and concentrate it to the center projecting it forward that gives it superior light collection ability.

These telescopes have the ability to view near earth (terrestrial) and outer-solar system (extra-terrestrial) objects better. The objects in our solar system, which are relatively bright, can be viewed with very rich results. So to, can it collect the faint light of far-away objects such as stars,nebulae and gas clouds. For viewing constellations or objects outside our solar system, the reflector has a the ability to concentrate very faint light into a viewable image. There are several types of reflector telescopes. The Newtonian is the option I will present here.

The principle of this type of telescope was invented by Sir Issac Newton in the mid-1660's using a concave primary mirror and flat secondary mirror configuration. (See images @ left) That basic design has proven to be very cost effective over many years, and one that has led to many manufacturers producing quality telescopes at reasonable prices. The early mirrors were made of an alloy of tin and copper that was highly polished using a fine pitch and lapping compound. Modern mirrors are made commonly of pyrex glass that has been ground using much more precise methods that produce very fine optical abilities. The early refractor telescopes produced images that had chromatic distortion errors that Newton hoped to correct.

He had a theory that white light was made up of a spectrum of color. It was that color presence that he felt caused chromatic aberration of the images seen through a refractor type telescope. Using his theory of color, Newton concluded that the chromatic defect was caused by the lens of the Refractor telescope behaving the same as the prisms he had experimented with. It is that: white light was being broken up into a rainbow of colors, which surrounded the celestial images he was viewing using a Refractor telescope. If this was true, he felt that chromatic aberration could be overcome by building a telescope that did not use lenses, but instead used mirrors. The result was a reflecting telescope. This eliminated the color fragmentation simply by collecting light and focusing it through a single lens. (Secondary) The advantages of Newtons' reflector design are as follows:

• Reflector images were free of chromatic aberration found in refractor telescopes.
• Newtonian telescopes were much less expensive to produce for a given size. That size is referred to as the aperture, or objective primary lens diameter. Simply stated, you can have a more powerful telescope (bigger mirror diameter) using his design, than you could get with a refractor telescope. The cost of producing large magnifying lenses was relatively more expensive then, as it is now.
• Because there is only one surface that needs to be ground into a complex shape, overall fabrication is far simpler and less expensive than refractors. A later design for refractors, the achromatic objective, required four lenses to correct for chromatic aberration. This need was side-stepped by Newtons' more practical design, effectively cutting costs.
• The reflector telescopes focal ratio can be obtained in a shorter focal plane. This means the reflector can focus an image in a shorter optical tube assembly, and will provide a wider field of vision at greater angles. This allows you to view a larger swath or open sky.
• The secondary lens is located at the top end of the telescope. This combined with the shorter focal ratios f8 and below, allow for a more compact mounting system. This reduced costs also, and added portability.

With this said, the Newtonian is not a perfect telescope by any means. It does have a few short comings to consider. These are as follows:

• Reflectors, like other telescope designs, suffer from coma, which is an off axis aberration that causes imagery to flare inwards toward the optical axis. Stars near the outer edge of a field of view can take on a cometlike shape. This is very apparent when taking photographs of galaxies and nebulae, especially when the focal length is f6 or below. The telescopes I present for you to consider have a focal ratio of f6-f7.68. As a beginner, and just learning astronomy, the issue of coma is not important. As you learn and seek to upgrade for astrophotography possibilities, the issue of coma will come into play. For the time being, coma is not a real issue because the naked eye view through a secondary lens will not be affected by coma to a degree that spoils viewing.
• Newtonian's all have a central obstruction caused by the mounting of the secondary diagonal mirror assembly. As you can see in the image three above left, the aperture (1) and primary mirror (2) is obstructed by a "spider assembly" (3) consisting of four vanes and a tube. The tube is cut of at a 45° angle allowing the diagonal mirror to mount and reflect light upward 90° into the secondary (4) lens. At first blush this looks very serious, but it is not because the focal plane is formed by all available lightentering the optical tube aperture. But, it does cause a reduction in image contrast. The amount of contrast lost will be directly related to the percentage of obstruction. Ideally, a good telescope will have a spider assembly that represents less than 15 percent aperture obstruction. The telescopes I present on this hub for you to consider have obstructions of less than 6 percent, and the contrast effect is minimal for this telescope type.
• For a portable Newtonian, meaning a telescope you wish to transport with you to the desert or mountains, has a problem with collimation. Collimation is the alignment of the primary mirror focal point (Center of Mirror), falling properly in alignment with the diagonal mirror. A telescope in transport is exposed to bumping and vibration. This can cause the mirror alignment to shift and the telescope fall out of collimation. The result is the collimation must be reset from time to time. Collimation is not difficult, and your telescope will come with direction on how to re-collimate the mirror easily. Other types of telescopes do not have this problem, a refractor for instance has a fixed collimation by design.
• Reflector telescopes have a asymmetrical focal plane. Because of this visual observation can become a problem when the optical tube orientation puts the secondary viewing lens high upwards. Meaning, When viewing an object that is straight overhead, a ladder may be needed to bring your eye level with the secondary lens for viewing. With the telescopes presented for your consideration in this hub, the optical tube length is not so long it will be a real problem. At most, a small step-stool may be required.

Having said all this, what must come clear is that a Newtonian reflector telescope is best for viewing objects that are both terrestrial and extra-terrestrial. This means that if you want to observe star clusters and constellations, the Newtonian Reflector is the best option because it has superior light collecting ability. It will collect more light with less distortion of the image viewed, using a larger aperture objective at less cost. It will also collect more light from dim objects and focus it on your Digital Single Lens Reflex Camera collector or slide film when you take timed photographs. Overall, the reflector is the option to choose for both viewing and photographing most near celestial objects, as well as more distant and faint outer solar system objects. It also offers a wider field of view.

I hope this article has helped you understand how a Reflector telescope works. Below I have placed a few suggested telescopes for your consideration. Additionally, you can view other options by visiting my blog site listed below, or visit my hub previewing Refractor and Dobsonian telescope design options.

 As children, our father introduced all six of us at an early age to the "wonders of astronomy" with the use of telescopes and later, camera photography of heavenly near and far objects.  The first purchase was a 3" Refractor Telescope with two extra lenses. We were deeply awed by the moon, planets, star clusters and constellations observed through this small telescope.  There is not one of us kids who would not later observe the heavens and site planets, common star clusters and constellations visible to the naked eye and not name them all correctly.

Later, our father built a 10" Reflector Telescope with a longer focal length, which took us to new dimensions allowing us to see deeper into space with more detail and resolution.  He hand ground the lens creating a concave mirror, rolled the tube, built the brackets and telescope mount.  After this he added tracking motors and a camera attachment for celestial photography.  The heavens were opened up exposing a beauty we all carry in our hearts to this very day.

Is This Real Quality Time?

Effective quality time can be measured.  Are we doing things as a group?  Is this a valuable learning experience?  Do emotions come into play that can be shared and remembered by everyone involved?  Are you exciting their enthusiasm in a way that is obvious and apparent?  These are assessment variables which in this case will be answered with a resounding yes.  The beauty and splendor of the universe will fascinate your children and friends.  Astronomy will never be seen as a wasted investment either in time, or money.

Portability is very important because quality time can include bringing the telescope on family excursions to the mountains and deserts.  Viewing and later photography (if you upgrade), is better in these locations because there is much less ambient light to interfere with viewing and photography.  The quality of celestial views and the photographs (time exposed), are excellent and will be shared and talked about for years to come.