I own a 500c/m and it came with a standard focusing screen. The screen is anything but "clean" and has a globular-shaped discolored area around the center of the image area that leads me to believe it was, somehow, left in the sun for a long, long time. Needless to say, I have great difficulty focusing in moderately subdued lighting. I would really like to own an Acute Matte screen for this camera but before I spend $300 on the little, square, semi-transparent contraption I have some concerns you may be able to alleviate or have a good solution for. I want grid lines. It is great using the spirit level for leveling the camera on a tripod but it would be so nice to have another means of aligning the horizon and verticals in a speedier (but still reliable) manner. The Acute Matte screen that comes with grid lines, unfortunately, also comes with a split-level rangefinder. According to the book "The Hasselblad Way" by H. Freytag (1978 ed., p 30) the split level rangefinder works with lenses through 150mm but not beyond. That is not the first time I've heard this. Others have complained of the split prism going dark under certain conditions -not just eye position- possibly a function of lens-speed/largest-apeture. Why this matters is that I use a 250mm Sonnar and would hate to not have the grid screen for use with this lens. Let me condense my questins here: Does the modern split image rangefinder work with the 250mm Sonnar? If the rangefinder image goes dark, can the regular screen area surrounding the split prism be used to achieve proper focus? Should I instead try to find and purchase the older "checked" screen with microprism center? Should I use a grid overlay on a blank Acute Matte screen? Help -I think I'm going insane!