To calculate the magnification, or power, of a
Telescope Focal Length (mm) = Magnification
Eyepiece Focal Length (mm)
For example, the Observer 70, which has a focal length of 700mm, used in combination with the 25mm eyepiece, yields a magnification of:
700mm25mm = 28x
Whatever you choose to view, always start by inserting your
Once you’ve centered the object in the eyepiece, you can switch to a higher magnification (shorter focal length) eye- piece, if you wish. This is recommended for small and bright objects, like planets and double stars. The Moon also takes higher magnifications well.
The best rule of thumb with eyepiece selection is to start with a low power,
What to Expect
So what will you see with your telescope? You should be able to see bands on Jupiter, the rings of Saturn, craters on the Moon, the waxing and waning of Venus, and many bright
Remember that you are seeing these objects using your own telescope with your own eyes! The object you see in your eye- piece is in
Objects to Observe
Now that you are all set up and ready to go, one critical deci- sion must be made: what to look at?
Magnification Limits
Every telescope has a useful magnification limit of about 2X per millimeter of aperture. This comes to 140X for the Observer 70. Some telescope manufacturers will use misleading claims of excess magnification, such as “See distant galaxies at 640X!”. While such magnifications are technically possible, the actual image at that magnifica- tion would be an indistinct blur.
Moderate magnifications are what give the best views. It is better to view a small, but bright and detailed image than a dim, unclear, oversized image.
A. The Moon
With its rocky surface, the Moon is one of the easiest and most interesting targets to view with your telescope. Lunar craters, marias, and even mountain ranges can all be clearly seen from a distance of 238,000 miles away! With its ever- changing phases, you’ll get a new view of the Moon every night. The best time to observe our one and only natural satel- lite is during a partial phase, that is, when the Moon is NOT full. During partial phases, shadows are cast on the surface, which reveal more detail, especially right along the border between the dark and light portions of the disk (called the “terminator”). A full Moon is too bright and devoid of surface shadows to yield a pleasing view. Make sure to observe the Moon when it is well above the horizon to get the sharpest images.
Use an optional Moon filter to dim the Moon when it is very bright. It simply threads onto the bottom of the eyepieces (you must first remove the eyepiece from the focuser to attach a filter). You’ll find that the Moon filter improves viewing comfort, and also helps to bring out subtle features on the lunar sur- face.
B. The Sun
You can change your nighttime telescope into a daytime Sun viewer by installing an optional
Important Note: Do not look at the Sun with any optical instrument without a professionally made solar filter, or permanent eye damage could result.
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