Celestron Onyx 80EDF User Manual

Congratulations on your purchase of the Celestron Onxy 80EDF telescope! Whether your interest lies in nature or celestial viewing the Onyx 80EDF telescopes offers the finest optical quality guaranteed to give you years of viewing pleasure.

		Onyx 80EDF
	Focuser Rotation		Sight Scope
					Extendable
	Locking Screw
					Lens Shade

2” Focuser (with

1.25” Adapter)

		Phototripod / Telescope
	Focuser Knobs
		Mounting Bracket

Photographic Tripod

For best results, attach your Celestron telescope to a heavy duty photo tripod or equatorial mount.

1.To attach to a standard photo tripod:

2.Align the hole at the bottom of the tripod mounting bracket with the ¼”x20 mounting screw on top of any standard photo tripod.

3.Thread the mounting screw into the tripod mounting bracket to secure the scope in place.

Equatorial Mount

Your Onyx 80EDF’s mounting bracket can be used with the Advanced GT CG-5 equatorial mount. Follow the directions in your mounts owner manual for instruction on attaching the optical tube.

VISUAL OBSERVING INFORMATION

Focusing

In order to focus your telescope for visual use it is necessary to use the appropriate diagonal and eyepiece. Celestron offers both 1.25” and 2” diagonals that are suited for both daytime (land) viewing and nighttime stargazing. See Optional Accessories section for more information.

1.When working with any optical instrument, there are several focusing hints that will ensure that you get the sharpest possible image. The hints listed here are for visual observing and photography.

2.Never look through glass. Glass found in household windows is optically imperfect and may vary

	in thickness from one location to the next. This inconsistency can and will affect the ability to
	focus your telescope. In most cases, you will not be able to	achieve a truly sharp focus. In some
	cases, you may actually see a double image.
3.	Avoid looking across or over objects that are producing heat	waves. This includes asphalt
	parking lots on hot summer days or building rooftops. The turbulent air caused by these
	conditions makes it impossible to get a truly sharp focus.
4.	Avoid hazy skies, fog, and mist, all of which can make it difficult to focus, thus greatly reducing
	the amount of detail seen. Remember that no matter how good the optics of your instrument are,
	they can NOT perform to their fullest under adverse conditions.

Calculating Magnification (Power)

You can change the magnification of your scope simply by changing the eyepiece (also called an ocular). To determine the magnification with your telescope, simply divide the focal length of your telescope by the focal length of the eyepiece. In equation format, the formula looks like this:

Focal Length of Telescope (mm)

Magnification = ___________________________________________________

Focal Length of Eyepiece (mm)

For example, to determine the magnification of the 80EDF with a 25mm eyepiece, divide the focal length of the telescope (500mm) by the focal length of the eyepiece (20mm). 500 divided by 20 yields 25 power.

Although the power is variable, each instrument has a limit to the highest useful magnification. The general rule is that 60 power can be used for every inch of aperture. For example, in a 3.2” diameter telescope, such as the 80EDF, the maximum useful magnification is 192 power. This is derived from multiplying 60 times 3.2”. Although this is the maximum useful magnification, most observing is done in the range of 20 to 35 power for every inch of aperture which for the 80EDF is 64 to 112.

Field of View

Determining the field of view is important if you want to get an idea of the size of the object you are observing. To calculate the actual field of view, divide the apparent field of the eyepiece (supplied by the eyepiece manufacturer) by the magnification. In equation format, the formula looks like this:

Apparent Field of Eyepiece (in degrees)

True Field (in degrees) =

Magnification

Using the example we started with in the previous section, we can determine the field of view using the same 25mm eyepiece. The 20mm eyepiece has an apparent field of view of 50°. Divide the 50° by the magnification, which is 25 power. This yields an actual field of 2°. To convert this to feet at one thousand yards, multiply the actual field of 2° by 52.5. This gives us a field width of 105 feet at one thousand yards.

PHOTOGRAPHY HINTS

Metering

Celestron telescopes have fixed apertures and, as a result, fixed f/ratios. To properly expose your subjects photographically, you need to set your shutter speed accordingly. Most 35mm SLR cameras offer through- the-lens metering which lets you know if your picture is under or overexposed. Adjustments for proper exposures are made by changing the shutter speed. Consult your camera manual for specific information on metering and changing shutter speeds.

Reducing Vibration

Releasing the shutter manually can cause vibrations, producing blurred photos. To reduce vibration when tripping the shutter, use a cable release. A cable release keeps your hands clear of the camera and lens, thus eliminating the possibility of introducing vibration. Mechanical shutter releases can be used, though air-type releases are best.

Blurry pictures can also result from shutter speeds that are too slow. To prevent this, use films that produce shutter speeds greater than 1/250 of a second when hand-

holding the lens. If the lens is mounted on a tripod, the exposure length is virtually unlimited.

Another way to reduce vibration is with the Vibration Suppression Pads (#93503). These pads rest between the ground and tripod feet. They reduce the vibration amplitude and vibration time.

ASTRONOMY WITH YOUR TELESCOPE

Observing the Moon

In the night sky, the Moon is a prime target for your first look because it is extremely bright and easy to find. Often, it is tempting to look at the Moon when it is full. At this time, the face we see is fully illuminated and its light is overpowering. In addition, little or no contrast can be seen at this time.

One of the best times to observe the Moon is during its partial phases (around the time of first or third quarter). Long shadows reveal a wealth of detail on the lunar surface. At low power you can see the entire lunar disk at one time. Change to higher power (magnification) to focus in on a smaller area.

Keep in mind that since you are not using a clock drive, the Earth’s rotation causes the Moon to drift out of your field of view. This effect is more noticeable at high power. You must manually adjust your tripod to