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Duncan Mask for SCT Collimation

A Duncan Mask can be used to easily and quickly collimate your SCT. Instructions are provided below.   
The mask comes in three sections that "snap-fit" together and can be taken apart for easier storage.  

Currently available for Celestron 8", 9.25", 11", 14"  and Meade 10" SCTs.  Feel free to contact me if you have a different scope.  


2-3 day Priority shipping available also.
International shipping calculated at checkout.

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Ships in 3-4 days.

Printed in durable, temperature tolerant PETG filament.

Instructions for use:

1.  Make sure your scope has cooled to ambient temperature.
2.  Point the scope at a bright star that is high in elevation.
3.  Place the mask on the scope.  Orient the mask such that the three snap fit connection lines point to the 3 collimation screws on the Secondary as shown in the scope image to the left.

4. A camera works best, but you can also use a a high magnification eyepiece.  Grossly defocus the star. You should see three arcs that correspond to the three cutouts.

5.  As you bring the star closer to focus the curves will change into lines pointing to a common center.  

6.  Use the lines to adjust the collimation screw opposite the line.  As you adjust the screw the line will move toward the center.  The goal is to form a perfect Y where the lines touch in the center.