Orion 90 EQ Eyepiece Selection, 1250mm ÷ 25mm =, Rotating the Diagonal, Objects to Observe

adapted, more stars will glimmer into view and you’ll be able to see fainter details in objects you view in your telescope.

To see what you’re doing in the darkness, use a red-filtered flashlight rather than a white light. Red light does not spoil your eyes’ dark adaptation like white light does. A flashlight with a red LED light is ideal, or you can cover the front of a regular incandescent flashlight with red cellophane or paper. Beware, too, that nearby porch and streetlights and car head‑ lights will ruin your night vision.

Eyepiece Selection

By using eyepieces of varying focal lengths, it is possible to attain many magnifications with the StarMax 90mm EQ. The telescope comes with one high-quality 25mm Sirius Plössl, which gives a magnification of 50x. Other eyepieces can be used to achieve higher or lower powers. It is quite common for an observer to own five or more eyepieces to access a wide range of magnifications. This allows the observer to choose the best eyepiece to use depending on the object being viewed.

To calculate the magnification, or power, of a telescope and eyepiece combination, simply divide the focal length of the telescope by the focal length of the eyepiece:

Magnification =

(focal length of telescope) ÷ (focal length of eyepiece)

For example, the StarMax 90mm EQ, which has a focal length of 1250mm, used in combination with the 25mm eyepiece, yields a power of

1250mm ÷ 25mm = 50x

Every telescope has a useful limit of power of about 2x per

mmof aperture (about 180x for the StarMax 90mm EQ). Claims of higher power by some telescope manufacturers are a misleading advertising gimmick and should be dismissed. Keep in mind that at higher powers, an image will always be dimmer and less sharp (this is a fundamental law of optics). The steadiness of the air (the “seeing") will also limit how much magnification an image can tolerate.

Whatever you choose to view, always start by inserting your lowest-power (longest focal length) eyepiece to locate and center the object. Low magnification yields a wide field of view, which shows a larger area of sky in the eyepiece. This makes acquiring and centering an object much easier. If you try to find and center objects with high power (narrow field of view), it’s like trying to find a needle in a haystack!

Once you’ve centered the object in the eyepiece, you can switch to higher magnification (shorter focal length eyepiece), if you wish. This is especially recommended for small and bright objects, like planets and double stars. The Moon also takes higher magnifications well.

Deep-sky objects, however, typically look better at medium or low magnifications. This is because many of them are quite faint, yet have some extent (apparent width). Deep-sky objects will often disappear at higher magnifications, since greater magnification inherently yields dimmer images. This is not the case for all deep-sky objects, however. Many galax‑

ies are quite small, yet are somewhat bright, so higher power may show more detail.

The best rule of thumb with eyepiece selection is to start with a low power, wide field, and then work your way up in magnification. If the object looks better, try an even higher magnification. If the object looks worse, then back off the magnification a little by using a lower-power eyepiece.

Rotating the Diagonal

When looking at objects in different areas of the night sky, the eyepiece may become positioned so that is uncomfort‑ able or impossible to look through. If the eyepiece is in an undesirable position, the diagonal can be rotated in order to provide a more comfortable viewing angle. First, loosen the thumb screws on the eyepiece adapter, but make sure to hold the diagonal in place so that it won’t fall to the ground. Also, secure the eyepiece in the diagonal so that it won’t fall out when rotating the diagonal. Retighten the thumb screws on the eyepiece adapter once the diagonal has been rotated to an appropriate position.

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?

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-chang‑ing phases, you’ll get a new view of the Moon every night. The best time to observe our one and only natural satellite is dur‑ ing 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 fil‑ ter). 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 full-aperture solar filter over the front opening of the StarMax 90mm EQ. The primary attraction is sunspots, which change shape, appearance, and location daily. Sunspots are directly related to magnetic activity in the Sun. Many observers like to make drawings of sunspots to monitor how the Sun is changing from day to day.

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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