NexStar Resource Site

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NexStar 80 Optics: Pinched and Out of Collimation

As reported in the May 2001 issue of Sky and Telescope, it is possible you might receive a NexStar 80 which exhibits poor optical quality.  The two common defects are pinched optics (shows itself by displaying slight corners on an out-of-focus star image) or poor collimation (shows itself by displaying a flare to one side of very bright stars).   Fortunately both problems are very easy to fix. 

These problems are related to how the achromatic doublet lens is held in the plastic mounting cell.  To access the mounting cell, pull off the lens/dew shade.  With pinched optics, the retaining ring is a bit too tight.  You can loosen the ring by unscrewing it (counterclockwise) by hand.  With poor collimation, you will find that the ring is too loose.  Using a cleaning cloth, press the front lens down all around the edges.  Then tighten the retaining ring by hand.

Additional improvements in the optical quality of the NexStar 80 can be found in Bob Berta's tune-up guide - click here to read.

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Michael Swanson
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