But you did not bother drawing the sketch, did you.
Try this.
Put your camera on a tripod.
Get a piece of string 15 feet long.
Tape it to the front of your camera.
draw a line on the ground with the heel of your shoe, or place a couple of soup cans and cereal boxes on the floor, so they are parallel to the camera, 15 feet in front of the camera (Imagine you are pointed straight at a barn wall, etc.)
Walk out the 15 feet to the end of the string, straight ahead of the camera.
The walk sideways, toward the side.
Does the string still reach to our imaginary barn, our line in the sand, or our row of cereal boxes and soup cans?
Or does the string not reach that far?
OR TRY THIS
Get a ruler.
Sit right in front of the middle of your monitor
Put the ruler up against your nose, so it just reaches the middle of your monitor.
Now rotate the ruler toward the edge of your monitor?
Without moving your head, does the ruler reach the edge?
BAK