The minimum recommended distance (in mm from the sensor to the tip of the nosepiece where the Star Analyser 100 screws in) is 4x the camera pixel size in microns. For example, for the ToUcam webcam, the distnce would be 5.6x4=22.4mm. If you find that the distance for your setup is less than the minimum value, we recommend purchasing sufficient spacers to bring the distance above the minimum.
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If you are still unsure whether you require a spacer please consult the calculator