Generally speaking the SynScanTM produces pointing and tracking accuracies adaquate for most applications. However, if higher precision is required, for example for astro-photography, accurate polar alignment and "cone" error calibration may be required. See the manual for HEQ51EQ6 mount for information on accurate polar alignment using the polarscope.
"Cone" error is a common inaccuracy found on all German equatorial mount. It is a result from the optical axis not being aligned to the R.A. axis of the mount. This affects the pointing accuracy of the SynScan'". Three-Star Alignment automatically compensates for the "Cone" error. If you choose One-Star or Two-Star Alignment method, you will need to perform manual mount calibration to eliminate the "cone" error. The following calibration procedure should be performed before the initial use of the telescope and periodically thereafter to ensure the accuracy.
Testing for Cone Error
This test is done at night using two bright stars located on the opposite side of the sky. Make sure the telescope is properly polar-aligned using the polarscope. Perform the One-star Alignment using an eastern star as the alignment star (see One-star Alignment). After the star alignment, choose a bright star on the western sky from the SynScanTMobject database and have the telescope slew to the star. If the optical axis is perfectly aligned to the R.A. axis, the telescope will accurately put the star in the center of the eyepiece. In this case, 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 is in the eyepeiece view and close to the center. Many factors determine the pointing accuracy of the SynScanrM,for example incorrect star alignment, R.A. or Dec lock knob being lose, or "cone" error. If your telescope puts the star outside the eyepiece view, you need to first determine whether it is "cone" error that causes the pointing inaccuracy. To find out, simply move the telescope in R.A. axis by pressing the Left or Right direction key. If the star can be moved into the eyepiece view without adjusting the Dec axis, it is likely that "cone" error exists in your telescope setup.
Calibration Procedure
1.Insert the illuminated reticle eyepiece. Make sure that the telescope is properly set up and balanced, and the finderscope is perfectly aligned with the telescope tube.
Step 2 to 4 is to identifi R.A. and Dec movements in the reticle eyepiece. If you are already familiar with the movcrnents, you may skip to step 5.
2.Find any bright star and place it in the center of the eyepiece view.
3.Look into the eyepiece. Move the telescope in R.A. axis using the R.A. direction keys on the hand control while carefully observing the movement of the star.
4.Keep moving the the telescope in R.A. axis back and forth to keep the star within the eyepiece view. Rotate the eyepiece until the movement of the star becomes parallel to (or matches) any set of the lines (Fig.A-1). This set of lines will represent R.A. movement in the course of this procedure, and the perpendicular lines will represent Dec movement. Tigthen the set screws to secure the eyepiece in place. Make sure that the eyepiece will remain stationary when the telescope is being rotated.
5.Point the telescope to North and set the latitude scale to your local latitude using the altitude adjustment T- bolts, or place Polaris on the crosshair of the polarscope if your polarscope is perfectly aligned with the rotation axis of the mount.
Required accessory. Illuminated reticle cyepiece with double crossline pattern. Depending on the design of your mounting plate (dovetail bar), modifications may be required. (See step 10 for the required mechanism on the mounting plate.)
movement
eyepiece view
