This is a finder screen mask for the CONTAX 645 system. This listing is for the 37x37 sensor size, as shown in the first photo. (The patterns in the second and subsequent photos are different and are for illustrative purposes only.) When using a medium format digital back, the shooting area of the sensor is smaller than the original film size. This mask is designed to be inserted into the screen to provide a guide for the actual shooting area. Since it's difficult to obtain the manufacturer's original product, I made this myself. I've found that I can mass-produce it, so I'm offering it to help others who have the same problem. It is handmade. Please note that the material is sensitive to moisture and oil. Please be careful to avoid contact with these substances. When attaching the mask, hold it by the edges and try to avoid fingerprints. The second and subsequent photos are examples of how it is attached. You will receive two finder masks. They are designed to be hooked onto the protruding part of the frame on the back of the finder screen, or attached to the frame with thin strips of double-sided tape. Please understand that this is a handmade item, and I cannot accept returns or exchanges except for critical defects or size errors. Representative compatible models for the 37x37 size include: * Phase One P20+/P20/H20 * Kodak DCS Proback 645C