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 buster to help keep the focusing screen as dust free as possible. They're readily available on Amazon or your local camera shop.
We do NOT recommend compressed air or canned air as they can damage the delicate focusing screen.