This is my first time to look at metadata and I’m confused by the focal length stated in this file that a friend e-mailed to me. It was taken with a cell phone.
I’m trying to roughly estimate the angle in degrees that corresponds to a width of 400 pixels in the 4096 × 2304 pixel image. If the no zoom was used, the focal length is 3.5 mm, the diagonal of 1/3.1 inch or 8.19 mm corresponds to 4700 pixels, and using trigonometry the angle from the center to the corner is about 49.5 degrees corresponding to 2350 pixel half-diagonal, giving roughly 47.5 pixels per degree. I used
(180/pi) * arctan2(8.1935/2., 3.5) = 49.5
But when I look at the metadata for the image I see
Digital Zoom Ratio: 1.4.
I am thinking that the image on the phone was zoomed by hand on the touch screen, and so I need to use a different focal length for my calculation.
Should I multiply the 3.5 mm focal length by a factor of 1.4 and then use the same math, getting a new estimate of about 39.9 pixels per degree?
(180/pi) * arctan2(8.1935/2., 3.5*1.4) = 39.9 Or am I missing something?