By Alain Dussault
Tools for observing
(Binoculars, Telescope)
Binoculars are the perfect tool to begin with in astronomy. Also, if after a certain time, your passion for astronomy decline, your binoculars will always be useful for terrestrial observation in general. for observing birds or a sporting event or animals. Binoculars are useful for the rest of your life, so it is important to make the good choice, before buying it.
Binoculars bear a pair of numbers in the form like 7 x 35, 7 x 50 or 10 x 40 and other combinations.
The first number represent the magnification of the binoculars: 7 mean that the instrument magnify seven times. The greatest tis number is, the greatest is the magnification, and the more details you can observe. But let say that a magnification greater than 10 is the maximum acceptable to be comfortable in observing things by holding its binoculars in our hands. In mounting the binoculars on a tripod, you can used a magnification greater than 10.
The second number represent the diameter in millimeter of the lens, named objective, from where the lights enter the binoculars. So 35 means that the diameter of the objectives are 35 mm( about 1.4 inches). the greatest this number is the more light goes through the instrument and what we see got more details.
The field of view is usually indicated in degrees, for example 5.2o. Then the greatest field of view the easier it will be to find or locate an object, but the more the quality of the optics must be. Other numbers might be indicated like, 640ft/1000 yds or 201m/1000m. These numbers means that at a distance of 1000m we see a width of 201m.
A good compromise will be to get a 7 x 50, binoculars.
Image quality of binoculars, depend on many factors. It is not easy, in a store, to judge the quality of binoculars in sighting a fixed object.
Binoculars are composed of two bodies that move to be able to ajust the eyepieces to suit our eyes separation. It is very important to check this point in the store. Make sure that the adjustment is adequate for you and others persons in your family. Check also that by bending these tubes, they are no play in the mechanism. If you wear glasses, verify also that the binoculars are comfortable with them on.
Then check the general quality of the binoculars. Are the axes of both eyepieces objective are parallels. A test to do is to look at a near and at a far object. You must see only one filed of view. If you see a double field of view, reject those binoculars.
Check that the binoculars focus to as near as possible. the more the focusing mechanism allow you to focus a near object, the better it is.
The eyepieces must be surround by a pliable rubber cup, or
a rigid and retractable one. Check that they feel
comfortable for you.
Optical quality
Try to check on an object in a dark area, to verify that the field of view is equally lighted. If on border things look blurred, then the optic is not of good quality.
If it is sunny outside, check that you do not see any disagreeable reflection in the binoculars.
Good shopping for binoculars.
It will serve you not only in binoculars or telescope
observation, but also allow you to take better photograph.
Here are the sites for manufacturers of these
types of telescopes and also of binoculars.You will be able to
see images of each types and complete description: http://www.celestron.com/
http://www.meade.com/
If we class them by order of increasing price, the cheapest are the Newton, then the Schmidt-Cassegrain, then Maksutov and the refractors.
The same criteria applies also to choose a telescope. Mechanical and optical quality.
A newton telescope is composed of only one principal mirror and a small secondary one called diagonal. These only two optical surfaces to grind, that is the main reason of its low cost.
Another important element to consider for a telescope, its it portability and it weight.
Do not evaluate a telescope by its magnification. So if
you intend to shop for a telescope, always go to special
astronomy store. Peoples there are usually astronomy
amateurs and can give you the best advise according to what you
intend to do with your instrument.
The best telescope will not be of much used, if it is placed on a fragile or instable mount. Any vibrations will affect the telescope, rendering impossible to get a neat image in it. You must then make sure that the tripod is robust, in wood or metal construction. The spread of the legs must be approximately equal to its height.
Recently many Newton type telescope are supplied with an azimutal mount of type Dobson. The advantage of this mount, is that the tube of the telescope is nearer to the soil, rendering the access to the eyepiece more accessible.
With an azimutal mount telescope, you need to constantly make corrections for pointing, in two axes at the same time, to be able to keep an object in the eyepiece field of view.
The equatorial mount though has the advantage of allowing one of it axe of rotation, parallel to the axis of rotation of the Earth. So by aligning this axis of the telescope on Polaris, give to the user, a longer time to look at an object, by having to make only small Right Ascension correction.
Certain type of equatorial mount are supplied with flexibles extensions, which allow to make adjustments in both Right Ascension and Declinaison, while keeping an eye in the eyepiece. This type of mount is the best one to look for, for non motorize one.
The focal length is teh distance that the light run between the front length in a refractor or the principal mirror, and the point where the image form. In general, the more the focal length, the more the object will appear.
The magnification is the ratio, between the focal length and the diameter of the eyepiece. If a telescope has a focal length of 2000 mm and is used with a 20 mm eyepiece, the magnification will be 100 times.
The price that you can afford to pay is the next criteria to take into account, if your interest in astronomy persist.
To be able to have access to any kind of celestial objects, and the planets, a good compromise is a 4 to 6 inches Newton telescope. Count from 600$ to 1000$ for a good one. Make sure that the viewfinder is of a very good quality. A poor viewfinder may lead you to leave your telescope in it case and your interest in astronomy will decreased rapidly.
Check that the telescope come with at least two eyepieces, One of 26 or 35 mm and the other of half a diameter, that is a 13 or 18 mm.
Your telescope must be portable and easily transportable in a car. The greater the mirror diameter the bigger and longer the tube of it will great and heavy.
If we offer you an eyepiece solar filter, refuse it, deal it for something else. A solar filter tobe safe must be place at the front end of a telescope.
A lunar filter to screw to an eyepiece is acceptable. The moon when it half lighted is very brilliant for the eyes, so a filter will allow you to attenuate this brilliancy and the observation of the moon will be more comfortable.
A recent new telescope from Meade, ETX 90 mm, un Maksutov, is to my opinion, a best choice for a first telescope at 859$ CAN. (595$US)
Next chapter, The References to help in
observing (Maps, Softwares, Internet)
Preceding chapter, Celestial coordinates and Universal Time, Star magnitude
Last update August 1st, 1999.