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TheCALCULATEmagnification, MAGNIFICATIONor power of a telescope is determined by two factors: the focal length of the eyepiece and the focal length of the telescope. Your telescope is sup- plied with one eyepiece. The focal length of the eyepiece, 26mm, is printed on its side. Telescope focal length is the distance that light travels inside the telescope before reaching a focus.
The focal length of the Dobsonian 8" = 1219mm. The focal length of the Dobsonian 10" = 1270mm The focal length of the Dobsonian 12" = 1524mm The focal length of the Dobsonian 16" = 1829mm
To calculatemagnification,the | of a given eyepiece, use this formula: | ||||
hange | change | yepi | s. | ||
| Power = Telescope Focal Length ÷ Eyepiece Focal Length | ||||
Example: Using the 26mm eyepiece supplied with the 8" f/6, the power is: | |||||
| Power = 1219mm ÷ 26mm = 47mm | ||||
The type of eyepiece, whether Modified Achromatic, Plössl, or Super Plössl, has no | |||||
effect on magnification, but does have a bearing on such optical characteristics as | |||||
field of view, flatness of field, and color correction. | |||||
Maximum practical magnification is about 50X per inch of aperture. Generally, how- | |||||
ever, lower powers produce higher image resolution. When unsteady air conditions | |||||
prevail (as witnessed by rapid “twinkling” of the stars), extremely high powers result in | |||||
distorted magnification and observational details are diminished by the use of | |||||
excessive power. |
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When beginning observations on a particular object, always start with a low power | |||||
eyepiece. Centered the object in the field of view. Sharply focus the object. Then try | |||||
using a higher power eyepiece. If the image starts to become fuzzy when you use | |||||
higher magnification, back down to a lower power. The atmosphere is not sufficiently | |||||
steady to support high powers. Keep in mind that a bright, clearly resolved, but | |||||
smaller image will show far more detail than a dimmer, poorly resolved larger image. | |||||
Obs ve duri | g the daytime: Try out your telescope during the daytime at first. It is | ||||
OBSERVING |
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easier to learn how it operates and how to observe when it is light. | |||||
Pick out an easy object to observe: | A distant mountain, a large tree, a lighthouse or | ||||
skyscraper make excellent targets. Point the optical tube so it lines up with your | |||||
object. |
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Use the red dot finder: If you have not done so, align the red dot finder with the | |||||
telescope’s eyepiece as described earlier. Look through the finder until you can see | |||||
the object. It will be easier to locate an object using the finder rather than locating with | |||||
the eyepiece. Line up the object with the finder’s red dot. | |||||
Lo k | rough the eyepiec : | Once you have the object lined up in the finder, look | |||
through the optical tube’s eyepiece. If you have aligned your finder, you will you see | |||||
the object in your eyepiece. |
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Focus: | Look through the eyepiece and practice focusing on the object you have | ||||
chosen. The focuser has both a lock knob and a tension adjustment knob. The first | |||||
lock prevents the draw tube (16) from moving in and out. The second lock locks the | |||||
focuser knob, thereby locking a focus position into place. Experiment with these knobs | |||||
to discover which adjustments are comfortable with your viewing style. | |||||
Observe | Moon: When you feel comfortable with the finder, the eyepieces, the | ||||
locks andthe adjustment controls, you will be ready to try out the telescope at night. | |||||
The Moon is the best object to observe the first time you go out at night. Pick a night | |||||
when the Moon is a crescent. No shadows are seen during a full Moon, making it | |||||
appear flat and uninteresting. |
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12 | Looking at or near the Sun will cause irreversable damage to your eye. Do not point | ||||
this telescope at or near the Sun. Do not look through the telescope as it is moving. |