National Geographic NG90EQ owner manual Using Your Telescope For Astronomical Viewing

The level of magnification required depends on the object being observed. Optimal performance is obtained if the magnification is typically not more than appromiately 30X for every 10 mm of objective lens diameter. Magnification of around 265X or less is ideal for a telescope with a 90-mm diameter objective lens and is best for observing most celestial objects. A lower magnification power and a wider field of view are advisable for the observation of galaxies and nebulae. The highest magnification power should be used for highly detailed observations of the moon, Jupiter and Saturn or any object that is quite bright.

The highest magnification power of the Barlow lens/9-mm eyepiece combination should only be used for large or bright objects such as the moon and the brightest planets.

We recommend that you begin all observation sessions with the 25-mm eyepiece alone. Then if more viewing power is desired you can either change the eyepiece, add the 3X Barlow lens, or do both. Be aware that as well as brightness being decreased there will come a point when image detail is also lessened. This is further impacted by air pollution, light pollution, and upper-air turbulence. Lower magnification powers lessen these effects.

A common mistake made by many beginners is to start an observation session by placing the high-power 9-mm eyepiece and the 3X Barlow lens in the telescope at the same time. This is an exremely high power, dim configuration that “sees” only a very small portion of sky and is therefore very difficult to aim.

USING YOUR TELESCOPE FOR ASTRONOMICAL VIEWING

1)Take your telescope outside. We do not recommend viewing objects through closed or open windows. Your view can be distorted by reflections in the glass of a closed window or by air currents of differing temperatures passing through an open window.

2)Let your telescope adjust to the outside temperature. Your telescope will perform much better if the temperature of the lenses and the air inside the tube are the same as the outside temperature. It may take up to 60 minutes to equalize the temperatures when the difference in temperatures is extreme.

3)Find a location far from glaring light. If you live in a large town or city, your viewing will probably improve the farther you move away from the city lights. The sky glow of a town or city can dramatically reduce the telescope’s performance and viewing capabilities.

4)Remove the round plastic dust cover (lens cap) from the front of your telescope.

5)Begin your viewing session by using the 25-mm eyepiece by itself. It will give you the widest angle and the brightest, sharpest views.

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