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Amazon.com : Astromania Bahtinov Mask Focusing Mask for Telescopes - FM180mm for a Tube Outer Diameter (OD) from 195mm-240mm - can be Mounted with The Brass Screws Inside or Outside The drawtube :
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Amazon.com : Astromania Bahtinov Mask Focusing Mask for Telescopes - FM120mm for a Tube Outer Diameter (OD) from 125mm-180mm - can be Mounted with The Brass Screws Inside or Outside The drawtube :
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Amazon.com : Astromania Bahtinov Mask Focusing Mask for Telescopes - FM200mm for a Tube Outer Diameter (OD) from 215mm-260mm - can be Mounted with The Brass Screws Inside or Outside The drawtube :
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Bahtinov and Tri-Bahtinov focus/collimation software - Equipment (No astrophotography) - Cloudy Nights
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