26Nov2015

Frequently Asked Telescope Questions

YES, it’s true! She’s looking through the wrong end.

It seems every week we hear stories from folk who have just bought a scope, or have had one for a long time and don’t know how to set it up and use it properly. See if you can relate to these.

I am assembling a reflector telescope. There are several screws at the bottom of the telescope that do not appear to be tight. Should I tighten these?

NO! These screws are used to align the primary mirror. If you tighten these, your reflector telescope will no longer be in alignment and images will suffer. Worse yet, the mirror may come loose in the cell and you will need to reassemble the telescope!

I have assembled my telescope. What adjustments do I need to make to my telescope before I begin to observe?

After your telescope is assembled, you will need to adjust the finder scope. The finder scope is the small telescope on top of the main telescope. When your finder scope is properly adjusted, any object you have centered in it will also be visible in the eyepiece of the main telescope. A little effort here will make the telescope much easier to use at night.

How do I adjust the finder scope?

It is easier to make the initial adjustment to your finder scope by day than to fumble around with the adjustments in the dark. Insert the eyepiece marked with the biggest number in the telescope. Focus on a distant object (far out on the horizon, if possible) and center it in the eyepiece field of view. Securely lock the telescope into position on the tripod. Adjust the finder scope (in its mount or with adjustment knobs if provided) until the object centered in the eyepiece of the telescope is also centered in the finder scope. When you begin your observing session under the stars, you will need to make more precise adjustments to your finder scope , but this will get you started.

Where is the best place to observe with my new telescope?

The best locations for astronomy will be rural areas far from large cities that pollute the night sky with outdoor lighting. This “light pollution” washes out many of the faint objects of interest to an astronomer, as does the light from the moon. A small telescope when used under a dark, moonless sky can match the performance of a larger telescope used under a light polluted sky or a moonlit sky. (Most astronomers do not hold the moon in high regard for this reason.)

I will be observing at home. Where should I set up my telescope ?

Not in your living room. Observing through the window of a house will drastically reduce the performance of your telescope. Go outside. If possible, set your telescope up away from buildings, parking lots, patios or other objects -wooden or cement – that absorb heat by day. These objects radiate heat back into the sky at night and will create air currents that degrade the images in your telescope . A backyard lawn, shielded from streetlights is a good place for suburban dwellers to begin.

Can I observe right away after my telescope is set up?

Yes, but your telescope won’t be operating at peak efficiency and neither will you.For you, it will take at least a half-hour of uninterrupted darkness for the pupils of your eyes to open to their fullest and be at their most sensitive to faint objects in the night sky. Furthermore, sudden exposure to bright light will quickly cause you to loose your dark adaptation. To read a star map or see the controls on your telescope , cover your flashlight lens with several layers of red plastic or paint it with several layers of red nail polish.

Red light has the least effect on dark-adapted eyes.For your telescope, it will require time for the optical system to “cool” to the temperature of the night air. While it is cooling, the lens or mirror will be changing shape and images produced will be distorted. Cool-down time is short with a small telescope, but it may take thirty minutes or more for a larger telescope to be at its best.

What else should I do before I begin to observe?

Dress warmly! The winter sky offers some of the best objects for a telescope and it is a shame to cut an observing session short because you didn’t bundle up. Even if you live in a warm area, or view during other seasons of the year, you will be surprised how quickly the air cools at night.

What does the number on the eyepiece mean?

The number on the eyepiece is the focal length of the eyepiece. It is not the magnification of the eyepiece.

How do I know what the magnification of the eyepiece will be?

The magnification of any telescope eyepiece used with your telescope will be the focal length of the telescope (consult your manual) divided by the focal length of the eyepiece. A telescope with a focal length of 1200mm will yield a magnification of 60x when you insert a 20mm eyepiece into the focuser. A telescope with a focal length of only 600 mm, however, will yield only 30x when used with the same 20mm eyepiece.

Which eyepiece should I use to begin observing?

ALWAYS start observing with the lowest magnification eyepiece available until you become skilled in the use of your telescope. This will be the eyepiece marked with the BIG number ( longer focal length ), not one of the smaller numbers. Again, the number you see on the eyepiece is the focal length, not the magnification.

Why should I start with a low magnification eyepiece?

A low magnification eyepiece has a wider field of view (the amount of sky you see when looking through the eyepiece) than a high magnification telescope eyepieces. The low-magnification eyepiece therefore makes it easier to “capture” an object you are trying to find in your telescope. Your lowest magnification eyepiece will also give you the sharpest image as well as the brightest image.

How do I use a high magnification eyepiece?

Once you have located an object with your low magnification eyepiece, move the telescope so the object is as close to the center of the telescope field of view as possible. Replace the low magnification eyepiece with one of higher magnification. If the object is not visible after you have changed to the high magnification eyepiece , go back to the low magnification eyepiece and start again.

Why do things seem to get darker as I increase magnification ?

A basic law of optics states that as magnification increases, image brightness decreases. In fact, if you increase magnification enough, an object will become too faint to see. This happens sooner in a small telescope than large telescopes.

What is a Barlow lens and how do I use it?

A Barlow lens is a lens that you use with your eyepiece. A Barlow lens will double (2x Barlow) or even triple (3x Barlow) the magnification of any eyepiece that you attach to it. To use a Barlow lens, remove the eyepiece from the focuser, insert the Barlow and then insert the eyepiece into the Barlow. Remember, though, that a Barlow is best used with low magnification (long focal length) eyepieces. When used with high magnification eyepieces, it may produce more magnification than your telescope can use.

Why do objects in the eyepiece drift out of the field of view after a few moments?

The telescope is not only magnifying the object you are observing in the sky, it is also magnifying the earth’s rotation! The more magnification you use in your telescope, the quicker an object drifts out of the field of view. Manual telescope mounts will require you to continually “recapture” the object by moving your telescope slightly. Motorized mounts move the telescope for you and keep the object in the eyepiece.

How much magnification should I use?

Use only enough magnification to provide a useable image. When you reach a point where the image has become so blurred as to lose useful detail, you are using too much magnification! At what point this happens depends on the object you are observing, the seeing conditions (atmospheric clarity and stability) and the size of your telescope (you can get more magnification out of a large telescope before images begin to blur).

What can I expect to see in my new telescope ?

You will be able to see many of the same things you see in magazines and books, but the images produced in your telescope will smaller and less spectacular. The images in magazines and books are produced by large observatory telescopes that take long exposure photographs with special cameras. It simply isn’t realistic to expect a small amateur telescope to produce visual images of the same quality.

If the images in my telescope are not as beautiful as what I have seen in pictures, why bother looking through my small telescope at all?

There is so much more to that little smudge of light you see in your eyepiece than meets the eye! Spend a little time and effort to learn about the things you see in your telescope and you will appreciate them much more. Remember, that little smudge of light may actually contain billions of stars and its light may have taken many millions of years to reach your telescope.

Besides, much of the thrill in amateur astronomy is seeing the glories of the night sky with your own two eyes. The difference between seeing a picture of Saturn in a book and seeing Saturn in your backyard through a telescope is a lot like the difference between seeing pictures of Alaska in a book and going to Alaska to see it for yourself.

Amateur astronomy is also about the challenge of finding faint, hard to see objects. This often frustrates the beginner (hence the popularity of computer GOTO telescopes) but it also keeps the die-hard enthusiasts out late into the night. Even if you use a GOTO telescope, you owe it to yourself to learn how to navigate by means of a star map . There are no words to describe the thrill of finally seeing a faint galaxy or nebula after several hours or even nights of looking for it.

* Lastly, there is a great amount of satisfaction that comes with knowing your way around the night sky. At a time when many of us feel alienated from the natural world, astronomy provides a way to reconnect to the universe around us. Ref. Optics Planet

 

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