To help with this predicament we have created the chart you see to the left. The focal lengths provided are accurate within the formula but may not represent actual manufacturers focal lengths. It should also be noted that this chart is for normal lenses and does not apply to wide angle formula lenses. The angles of view are given in both diagonal and horizontal degrees, some of the horizontal measurements are not available but are generally 12 to 17% less than diagonal. For most applications the horizontal angle of view is used, this gives the angle from left to right. All angles of view are based on 35mm format and are approximate for other formats. Please feel free to print this chart and use as an aid in focal length equivalents.
To utilize this chart simply find the format and focal length you are starting with and then locate the equivalent focal length in the format you will be using. The angle of view will be in the two right hand columns.