I just bought a simple ME metering prism finder S for my Bronica SQ-A at auction. Whenever I point it at something and press the silver button on the side for a reading, I get a red light, indicating underexposure. I have set it at various exposures down to 1 sec at f2.8 but even when I point straight at a 100w light, I am still getting an indication of underexposure. How does the meter know what film speed to work with? I dialled in 400asa on the film back, but can the meter pick up this info? Is that the right thing to do? It could need calibrating. Does anyone have experience of using these meters?