Archived posting to the Leica Users Group, 1999/01/09
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]At 08:53 AM 09/01/99 -0700, Joe wrote: >I looked up "rainbow" in MS Encarta (1996). ... The original question asked for the focal length required to include BOTH the primary and secondary rainbows, so that nothing would get cut off by the edge of the frame. To the top of the secondary rainbow, the angle of view from the observer is 50 degrees. That means that to be able to see the entire arc, from the left to the right horizon, you need to enclose an angle of view of at least 100 degrees. Before I said that a 21mm lens is not quite wide enough to include full coverage. Part of the rainbow will be cut off by the edge of the frame. The reason for this is that in 35mm format, a 21mm lens only has an angle of view of about 91 degrees, which is just shy of what is required to include BOTH primary and secondary rainbows. Raimo said he got this in the frame with a 35mm lens at sea level. I'm not sure if he just meant the primary rainbow or both. It's hard to believe, but I'll take his word for it, remaining fully skeptical. I can only get both full rainbows in with a 17mm lens where I am, at 580m above sea level. I have no idea why this is so. If someone has a copy of "Galen Rowell's Vision" handy, check his full circular rainbow shot taken from a small airplane. As I recall when I read this some time ago, I think he used a 24mm lens, but I could be mistaken. (Going from memory, I think it may have been taken with a 24mm lens only because I know he uses that lens and an 85mm for most of his work.) As others have mentioned, it may be likely that various focal lengths can be used, depending on how high you are above sea level. I think I remember seeing something in one of Brian Bower's books (maybe the newer version of Leica Reflex Photography with newer info on the R8) taken with a 21mm Super Angulon on either an M4-P or an M6 which shows a (nearly) complete double rainbow, but just slightly too narrow to get it all in. Dale's reference to the site <http://www.howstuffworks.com/question41.htm> doesn't mention anything about the effect of altitude on the viewing angle, so it doesn't add much to the background information.