Here's the calculator;s author;s method of calculating the angle. Note there are two methods. Which one is wrong or both?
calculator site with explanation
Angle and Field of View
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θ the angle of view
s is the focus distance
h is the frame dimension
f is the focal length |
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The calculator calculates angle of view using two different methods. Both arrive at the same result at infinity focus, but differ at closer focusing distances. Since fields of view are calculated using the angle of view, there are also two calculated values for the field of view at the specified distance; one for each method. Further, neither method is completely accurate at very close focusing distances. For more information on this, see
Calculating the Angle of View: When Theory Meets Practice.
Method 1 is a “naive” method that assumes that the angle of view for the format, which is the angle of view at infinity focus, does not change when the lens is focused closer.
Method 2 compensates for lens extension when focusing closer than infinity.
Which method should you use?
Use Method |
Does your lens extend when focusing? |
2 |
Does your lens use an inner focusing system or is a video or cine lens? |
1 |