The Wratten G is a deep yellow, darker than the K2 filter. The G has a filter factor of 3 while the K2 has a filter factor of 2 with panchromatic film. I have several of the Series VI and when they fade it is usually in the center and not uniform. There is definately no convex glass. The Portra lenses are the magnifying lenses. Today we call the K2 a No. 8 and the G a No.15.