Archived posting to the Leica Users Group, 1999/01/14
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]If you see a rainbow, it is as if you are looking into a cone with an angle of 80° to 84°, depending on the colour you look at. (I did not check these figures, so I cannot guarantee them, but the other observations are purely mathematical and seem to be sound). Depending on your personal position vs the sun's position this cone can have different directions. The sun is always on the line going through the center of the cone but in the direction behind you. Thus we usually see only part of the cone the other being hidden below the horizon. If you are in a plane you might see a whole circle. The 24mm focal length has an angle of view of 84.06°, the 21mm has 91.7°. This is the angle of the diagonal for the lens at infinitiy setting. The angle of view for a complete circle (or the cone from above) is 53,13° for the 24mm lens and 59,5° for 21mm. To get a complete cone of 84 degrees on 24x36mm negative you need a focal length of 13.8 mm. If you are interested in the calculations to find some hidden errors (well I am so human) please feel free to ask. Besides I prefer to use the viewfinder to know what will be on the film. christoph