Orion 9786 Astroimaging with the 6 Newtonian Imaging Reflector, Collimating the Optics

divide the focal length of the telescope by the focal length of the eyepiece:

1.25" nosepiece

Telescope Focal Length (mm)

Eyepiece Focal Length (mm)

= Magnification

For example, the 6" Newtonian Imaging Reflector, which has a focal length of 750mm, used in combination with a 25mm eyepiece, yields a magnification of

750 mm	= 30x
25 mm

Every telescope has a useful limit of power of about 45x-60x per inch of aperture. Claims of higher power by some tele­ scope manufacturers are a misleading advertising gimmick and should be dismissed. Keep in mind that at higher pow­ ers, an image will always be dimmer and less sharp (this is a fundamental law of optics). The steadiness of the air (the “seeing”) will usually limit how much magnification an image can tolerate.

Always start viewing with your lowest-power (longest focal length) eyepiece in the telescope. After you have located and observed the object with it, you can try switching to a higher- power eyepiece to ferret out more detail, if atmospheric con­ ditions permit. If the image you see is not crisp and steady, reduce the magnification by switching to a longer-focal-length eyepiece. As a general rule, a small but well-resolved image will show more detail and provide a more enjoyable view than a dim and fuzzy, over-magnified image.

Astroimaging with the 6" Newtonian

Imaging Reflector

The 6" Newtonian Imaging Reflector has been specifically designed for use with astronomical CCD imaging cameras like the Orion StarShoot, but other imaging systems such as digital SLR cameras will also work well with the telescope. The secondary mirror of the 6" Newtonian Imaging Reflector has been sized appropriately to provide a fully illuminated field of view for Orion StarShoot cameras and most popular digital SLR models.

Unlike most Newtonian reflector designs, the 6" Imaging Reflector's secondary mirror has been recessed further into the tube to prevent off-axis glare from being detected by imag­ ing devices. Glare can contaminate night-sky images by reduc­ ing image contrast and giving the object a “soft” appearance.

To use your CCD camera with the 6" Newtonian Imaging Reflector, the camera must have a 1.25 inch “nosepiece”. Otherwise an external camera adapter with T-threads is required. All Orion StarShoot cameras feature this nosepiece (Figure 2). Insert the nosepiece equipped camera into the focuser just like an 1.25" eyepiece.

If your camera does not include a 1.25" nosepiece, you have a digital SLR, or if you wish to utilize a secure T-thread con­ nection with a CCD camera like the Orion StarShoot, a zero- profile camera adapter is required (available from Orion). The zero-profile adapter is inserted into the focuser just like a 2" eyepiece and provides T-threads for attachment of digital SLR T-rings or T-threaded CCD cameras.

Figure 2. To use a CCD camera with the 6" Imaging OTA, the camera must have a 1.25” nosepiece, like the Orion StarShoot Imaging cameras, or else an external camera adapter with T‑threads is required.

To attach a digital SLR to the telescope, remove any attached lenses and connect a model-specific T-ring to the camera body. Thread the T-ring onto the zero-profile adapter to com­ plete attachment. To securely attach a CCD imaging cam­ era like the Orion StarShoot via T-threads, remove the 1.25" nosepiece and thread the CCD camera onto the zero-profile camera adapter to complete attachment.

Due to its imaging-optimized design, no external extension tubes are required to appropriately couple the telescope to an imaging camera.

To record an image of a night-sky object, you will need to first acquire and center the object with an eyepiece.You may need to extend the focuser’s built-in extension tube to achieve focus with an eyepiece. Once you have centered the target object in the eyepiece field of view, remove the eyepiece and insert your CCD camera into the telescope’s focuser (don’t forget to retract the built-in extension tube if it has been extended). Secure the camera with the thumbscrew on the focuser. Use the focus and fine-focus wheels to bring the image into focus.

Collimating the Optics

Collimating is the process of adjusting the mirrors so they are aligned with one another.Your telescope’s optics were aligned at the factory, and should not need much adjustment unless the telescope is handled roughly. Accurate mirror alignment is important to ensure peak performance of your telescope, so it should be checked regularly. Collimating is relatively easy to do and can be done in daylight.

To check optical alignment, remove the eyepiece and look down the focuser drawtube. You should see the secondary mirror centered in the drawtube, as well as the reflection of the primary mirror centered in the secondary mirror, and the reflection of the secondary mirror (and your eye) centered in the reflection of the primary mirror, as in Figure 3a. If anything is off-center, proceed with the following collimating procedure.

The Collimating Cap and Primary Mirror Center Mark

Your 6" Newtonian Imaging Reflector comes with a collimat­ ing cap. This is a simple cap that fits on the focuser drawtube like a dust cap, but has a hole in the center and a silver bot­

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