Operating the 8 f/4.0 Newtonian Astrograph

Black collimation knob (x3)

Back of primary mirror

Cooling fan

White lock knob (x3)

Power jack

Figure 5. Rear of telescope showing the installed cooling fan and six collimation adjustment knobs (three black collimation knobs and three white lock knobs).

is centered on the crosshairs of the finder scope and in the telescope’s eyepiece, the finder scope is aligned and ready to be used for locating objects.

The finder scope alignment should be checked before every imaging or observing session.This can easily be done at night, before viewing through the telescope. Choose any bright star or planet, center the object in the telescope eyepiece, and then adjust the bracket’s alignment screws until the star or planet is also centered on the finder’s crosshairs.

Focusing the Finder Scope

If the image in the finder scope appears out of focus, you will need to refocus the finder scope for your vision. First, loosen the lock ring located behind the objective lens cell on the body of the finder scope (Figure 3). Back the lock ring off by a few turns. Then refocus the finder scope on a distant object by rotating the objective lens cell clockwise or counterclockwise. Once the image appears sharp, retighten the lock ring behind the objective lens cell. The finder scope’s focus should not need to be adjusted again.

Operating the 8" f/4.0 Newtonian Astrograph

Your 8" f/4.0 Newtonian Astrograph is designed primarily for astro-imaging, but it makes a fine visual instrument as well. For visual use, we recommend using high-quality eyepieces to take full advantage of the instrument’s exceptional optical quality. For imaging applications, the telescope is optimized for use with an APS-C size sensor, found in such cameras as the Orion StarShoot™ Pro, Orion Parsec™, and many DSLRs.

Cooling the Telescope

All optical instruments need time to reach “thermal equilibri- um.” The bigger the instrument and the larger the temperature change, the more time is needed. Allow at least 30 minutes for your telescope to cool to the temperature outdoors. In very cold climates (below freezing), it is essential to store the tele- scope as cold as possible. If it has to adjust to more than a 40°F temperature change, allow at least one hour. You can use the telescope while it’s cooling down, just note that you may see “tube currents,” which interfere with the telescope’s ability to resolve a sharp image. Tube currents are essential- ly heat waves exiting both the optical components (such as the primary mirror) and the telescope itself. The effect seen through the eyepiece is much like looking above a hot surface or fire.

Mirror Cooling Fan

The 8" f/4.0 Newtonian Astrograph comes with a cooling fan installed on the rear of the primary mirror cell (Figure 5). Using the fan reduces the amount of time required for the pri- mary mirror to reach thermal equilibrium with the ambient air. The fan is powered by 12-volts DC. The included battery hold- er holds eight AA alkaline batteries (not included). Plug the cable from the battery holder into the fan’s power jack located on the rear cell. Alternatively, the fan can be powered by a 12-volt DC field battery, such as the Orion Dynamo Pro.

You can run the fan prior to starting your imaging or observing session, then turn it off, or keep it running during the ses- sion, as there should be no noticeable vibration. However, it is probably not necessary to run the fan continuously for long periods of time, unless the temperature is changing continu- ously and rapidly.