Angle of Coverage Vs Image Circle

[cp]

hi, dear all, as a green LF user( actually a pre LF user), i would like to ask the followings: 1/what 's the difference of angle of coverage and image circle? are they 2 different parameters describing the same thing? 2/ what is the practical significance of these parameters? of course, , without considering the price,greater angle of coverage, larger image circle the best,ri ght ? but how can i assess the optimal angle of coverage of a specific lens when i buy , esp with camera movement adopted, before actually seeing it in the CG? thanks benz

[Glenn Kroeger]

Benz:

Angle of coverage and image circle are directly related to one another and the focal length of the lens. Excuse the math, but:

(ImageCircleDiameter/2)/FocalLength = tan (AngleOfCoverage/2)

[David A. Goldfarb]

More coverage gives more room for camera movements, usually at greater cost and greater weight and potentially loss of contrast due to the excess light bouncing around in the camera. Note that the coverage circle given is usually for the lens focused at infinity, while the angle of coverage is constant at any distance.

If you are photographing architectural subjects with a wide angle lens, go for all the coverage you can afford. If you are shooting landscapes with long focal length lens for your format, you might not need the maximum coverage version of the lens, since long focal lengths (non-telephoto designs) tend to have a large coverage circle to begin with, landscapes don't often require extensive movements, and you might not want to carry the weight of several big-coverage lenses if you are backpacking. An enormous coverage circle is usually unecessary for portraits, since you are not likely to be focused at infinity, and the lens will have a greater coverage circle at typical portrait distances.