some early slrs featured a built-in cds meter usually on the front left side of the top plate, as in the minolta sr-7. other manufacturers, such as miranda and nikon introduced a cds prism which fitted to their interchangeable prism slr cameras. nikon's early photomic finder utilized a cover in front of the cell which was raised and a reading was taken and the photographer would either turn the coupled shutter speed dial and/or the coupled aperture ring to center a galvanometer-based meter needle shown in the viewfinder. the disadvantage of this early photomic prism finder was that the meter had no on/off switch so the meter was constantly 'on', thus draining battery power. a later photomic housing had an on/off switch on the pentaprism. cds light meters proved more sensitive to light and thus metering in available light situations was becoming more prominent and useful. further advances in cds sensitivity, however, were needed as cds cells suffered from a 'memory effect'. that is, if exposed to bright sunlight, the cell would require many minutes to return to normal operation and sensitivity.