Orion 7817 Technical Specifications, Appendix A Enhancing the Precision, Cone Error Calibration

3. Technical Specifications

Motor drives:	Dual-axis, GoTo comput-
	erized.
Operation:	Northern or Southern
	hemisphere
Autoguiding rates:	1.25X / 1.5X / 1.75X / 2X
	sidereal rate
Power requirrement:	12V DC, 2A (tip posi-
	tive)
Motor type and resolution:	Microstep driven
	stepper motors
Slew speeds:	Rate 0 = 1.5X
	Rate 1 = 2X
	Rate 2 = 8X
	Rate 3 = 16X
	Rate 4 = 32X
	Rate 5 = 64X
	Rate 6 = 400X
	Rate 7 = 500X
	Rate 8 = 600X
	Rate 9 = 800X (3.4°/sec)
Tracking rates:	S i d e r e a l ( d e fa u l t )
	lunar, solar, PEC +
	sidereal.
Tracking modes:	R.A. tracking
Alignment method:	One-star alignment, two-
	star alignment, three-star
	alignment
Database:	25 user-defined objects,
	complete M, NGC. and
	IC catalogs, total 13,436
	objects.
Pointing accuracy:	Up to 1 arcminute with
	cone error calibration, up
	to 15 arcminutes without
	cone error calibration

This device complies with Part 15 of the FCC Rules. Operation is subject to the following two conditions: (1) this device nay not cause harmful interference, and (2) this device must accept any interference received, including interference that may cause undesired operation.

Changes of modifications not expressly approved by the party responsible for compliance could void the user’s authority to operate the equipment.

Note: This equipment has been tested and found to comply with the limits for a Class B digital device, pursuant to Part 15 of the FCC Rules. These limits are designed to provide reasonable protection against harmful interference in a resi-

dential installation. This equipment generates, uses and can radiate radio frequency energy and, if not installed and used in accordance with the instructions, may cause harm- ful interference to radio communications. However, there is no guarantee that interference will no occur in a particular installation. If this equipment does cause harmful interference to radio or television reception, which can be determined by turning the equipment off and on, the user is encouraged to try to correct the interference by one or more of the following measures:

-Reorient or relocate the receiving antenna.

-Increase the separation between the equipment and receiver.

-Connect the equipment into an output on a circuit different from that to which the receiver in connected.

-Consult the dealer or an experienced radio/TV technician for help.

A shielded cable must be used when connecting a peripheral to the serial ports.

Appendix A: Enhancing the Precision

The Skyview Pro GoTo system produces pointing accuracy and tracking accuracy adequate for most applications. If higher precision is required, “cone” error calibration may be necessary.

Cone Error Calibration

“Cone” error is a common inaccuracy found on all German equatorial mount designs. Cone error results from the optical axis of the telescope not being aligned to the R.A. axis of the mount. This affects the pointing accuracy of the GoTo sytem. Three-star alignment automatically compensates for some of the “cone” error, but pointing accuracy will be optimized by mechanically minimizing the “cone” error. The following cali- bration procedure should be performed before the initial use of the telescope and periodically thereafter to ensure peak accuracy.

Testing for Cone Error

This test is performed at night using two bright stars located on opposite hemispheres of the night sky. Confirm that the telescope is properly polar-aligned using the polar axis finder scope. Perform the one-star alignment using an eastern star as the alignment star (see “One-Star Alignment”). After com- pleting the star alignment, choose a bright star in the western sky from the GoTo hand contoller's object database and press ENTER to slew the telescope to the star. If the optical axis is perfectly aligned to the R.A. axis, the telescope will accu- rately put the star in the center of the eyepiece. This shows that there is no “cone” error in your telescope setup and you will not need to perform the calibration. It is acceptable if the star is slightly off-center as long as it appears in the eyepiece field of view and reasonable close to the center. Many factors determine the pointing accuracy of the GoTo hand contoller's.

15