TTV stands for Through The Viewfinder. A picture is taken through the optics of another camera. I used my Sony digital to shoot the viewfinder of an old twin lens camera. Usually the attempt is to get the old photo look by leaving the dirt on the glass and mirror. I took my old camera apart and cleaned it. It will get dirty again soon enough. I just bought it yesterday so I have yet to make a contraption to hold my taking camera at the right distance. This will help make the shooting easier by aiding focusing and exposure.