Do I need anything else to get started? - Beginning Deep Sky Imaging - Cloudy Nights
158-193mm ID Orion PinPoint Telescope Focusing Mask (Bahtinov) | Astromart
How to Use a Bahtinov Mask | Easiest Way Focus Your Telescope
Bahtinov Masks | OPT Telescopes
Orion 58 - 93 mm ID PinPoint Telescope Focusing Mask
Amazon.com : Astromania Bahtinov Mask Focusing Mask for Telescopes - FM60mm for a Tube Outer Diameter (OD) from 65mm-100mm - can be Mounted with The Brass Screws Inside or Outside The drawtube :
How to Use a Bahtinov Mask | Easiest Way Focus Your Telescope