BetterPhoto Member |
lens angles on the ground Hi, I would like to know how the focal length of the lens translates into the angle of view seen in the photo. I am taking repeat photos of various landscapes and to analyse the changes seen in the photo pairs I need to know more precisely how the lens I use relates to amount of view seen in the photograph. To clearify what I need: imagine a topographic map with a red dot on it representing the location of the camera when the photo was taken, then imagine two lines drawn outward from the dot in the direction the shot was taken forming a V shape representing the field of view of the photo. I want to know what the angle degree is of the V depending on the lens that I use. This will help me analyse how much map area is covered by the photograph. I hope you can answer my question. Thank you, Monica Bueno
|
||||||||||
|
|||||||||||
John A. Lind |
Dust off your trigonometry from school . . . First: The FOV is directly related to the focal length and the size of the film frame. Assuming your are using 35mm "small format" the film frame is 36mm wide by 24mm tall. Imagine a triangle, the base of which is the width of the film frame and the height of which is the focal length. The Horizontal Field of View (HFOV) is the angle at the apex. The math for this is: This equation makes use of the fact that the tangent of an angle is its ratio of vertical rise to its horizontal run, which covers half the field of view. For a 50mm standard lens the HFOV is about 40 degrees. I've uploaded a diagram showing how this works. It's to scale for a 50mm standard lens, but the math works for any focal length. If you turn the camera vertical, substitute "24/2" (or 12) for the "36/2" (or 18) in the equation. Because the vertical height of the film frame is smaller, the VFOV is smaller than the HFOV. Note: -- John
|
||||||||||
|
|||||||||||
This old forum is now archived. Use improved Forum here
Report this Thread |