This non-illuminated 18mm polar alignment finderscope is an option for the current Celestron CG-4 and Omni Series German equatorial mount scopes only. It contains a reticle with patterns for polar alignment in both northern and southern hemispheres. It will not work with CG-5 and Advanced Series mounts. For a polar finder for a CG-5, Advanced Series mount, or AVX, use our part #3910.
This new finder threads into the rear of the polar axis of your mount after removing the black ring with three chrome thumbscrews from the mount. The chrome thumbscrews were used to collimate the previous version of the finder, but were susceptible to damage in transit and use. Instead of using the three exposed chrome thumbscrews to collimate the finder with the rotation axis of the mount, this new finder uses three small setscrews in the finder body to accurately align with the axis of rotation of the scope. Their recessed location makes them essentially immune to damage or accidental miscollimation. One of the setscrews is visible, but just barely, in the close-up photo. It is located at the 12 o'clock position at the top of the finder between the eyepiece and the aluminum trim plate.
Aligning the finder to the mount's axis of rotation is a one-time procedure that takes only a few minutes and is done during the day. Full instructions are included with the finder. The finder can be left installed in the mount permanently.
Once aligned, to use the polar finder each evening thereafter in the northern hemisphere, the mount is first roughly aligned on the north celestial pole. The scope is rotated in right ascension until the stars in either Cassiopeia or the Big Dipper line up with the corresponding constellation pattern etched in the finder reticle. The mount's right ascension clutch is locked firmly so the mount can't lose its orientation on the stars. The altitude and azimuth controls are then adjusted to move the mount while looking through the polar finder until Polaris falls into a small circle etched into the reticle. When Polaris is located within the circle, the axis of rotation of the mount is aligned on the north celestial pole (not just on Polaris) with enough accuracy to permit casual long exposure guided astrophotography for the evening.
A similar procedure is used in the southern hemisphere, except that the Constellation Octans is used instead of Cassiopeia or the Big Dipper. After rotating the mount until Octans lines up with its reticle pattern, the altitude and azimuth controls are adjusted until the stars in Octans fall into the appropriate circles in the Octans reticle pattern.
