The Telrad Dew Shield helps keep condensation from forming on the glass plate of your Telrad. It can be flipped completely over the glass while you're getting that cup of coffee and then rotated upward to allow you to see through to the sky. The Dew Shield Plus offers the same protection but with a bonus. Inside the Dew Shield Plus is a mirror. When the shield is rotated completely backwards, the mirror acts as a right angle viewing device, letting you see the reticle in the sky without bending over the telescope or twisting your neck.