51mm Carl Zeiss of Jena Gelbglas light yellow filter. Comparing this filter to other filters I own, I believe it would be classified as a light yellow, Kodak K1 or number 6, Tiffen Y1, Leitz Y0. If so, it would have a filter factor of 1.5X (or plus 2/3 stop). Fits Zeiss Primoplan Pancolor 58mm lens.

Used but in good condition, slight brassing and fading to the lettering. Glass has some tiny, almost invisible imperfections that would not affect image quality.

Black and white film is overly sensitive to blue light, so skies tend to appear white. A yellow filter filters out some of the blue light, giving the sky some tone in the print and allowing for contrast between sky and clouds. A yellow filter also may lighten foliage.