The B&W 27 mm KB1.5 (82A) Color Conversion Glass Filter is a light balancing filter used to increase the color temperature slightly for a cooler tone. This blue filter absorbs the excessive yellow-red light from daylight in the morning.
There is much flattering light to be found in the early morning and afternoon hours. With sunlight low on the horizon, the red-orange end of the spectrum becomes enhanced. With daylight balanced film, images shot in this light may prove to be a bit on the warm side. The photographer may desire this effect or choose to "cool" things down.
An 82A has a greater "cooling" effect than an 82 but less than an 82B. The 82 series of blue filters allows the photographer to keep skin tones somewhat normal by increasing the color temperature to a more daylight balanced level. In addition, an 82A provides a cooler effect with tungsten film under 3200K lamps.