Dust is the enemy in photography of any kind. In the darkroom, on your lens, on the sensor in your digital camera, it gets everywhere.
When you take a photograph with ObscuraFlex™ it's a little like taking a photograph of a negative or a slide, any dust sitting on the surface of that negative will show up in your exposure.
For this reason we suggest getting a dust blower to help keep the focusing screen as dust free as possible. They're readily available on Amazon or your local camera shop.
DO NOT use compressed/canned air as they can damage the delicate focusing screen.
DO NOT use your breath as droplets of moisture may mark the screen.