This is a mask for the viewfinder screen of the CONTAX 645 system. The one in the photo is for a 37x37 sensor size, with the area outside the shooting range shaded, but I can make it in your desired size and with or without shading if you leave a comment. (3-split, 4-split, and cross grid options are also available) When using a medium format digital back, the shooting area of the sensor is smaller than the original film size, so you can use this mask to get an idea of the actual shooting area by inserting it into the screen. I made this myself because it's difficult to obtain the manufacturer's genuine product. I realized I could mass-produce them, so I made them by hand in the hope that they would be helpful to those with the same problem. Please note that the material is sensitive to moisture and oil, so please be careful not to get any on it. When attaching the mask, hold it by the edges and try not to get fingerprints on it. The method of attaching it to the camera is as shown in the photo, but it is intended to be inserted into the frame on the top of the viewfinder screen, taking care not to get fingerprints on it. Please understand that this is a handmade item, so please refrain from returns or exchanges except for fatal defects or size errors. Typical compatible models for the 37x37 size include: - Phase One P20+/P20/H20 - Kodak DCS Proback 645C