Focal Length and Angle of View
Below are 5 photographs I took of this sundial in Richmond Park. I took 2 additional images as I wasn't sure which focal lengths would produce the results I was aiming for. The photographs were taken from the same spot, and working down through the images we can see an increase in focal length and a narrowing of the field of view. The second image, with a focal length of 32mm (an equivalent focal length (efl) of 48mm) is closest to 'standard' focal length, or an approximate view as seen by the human eye. The equivalent focal length is calculated by multiplying the focal length of the lens by the crop factor associated with the camera's sensor. In this case it is 1.5.
Having printed the images onto A4 paper, I returned to the same spot and began by holding the 32mm image in front of me, comparing the size of the sundial in the image with the real thing. The images matched up when the print-out was around 55cm from my eye (around a full arm's length). Switching to the 18mm print-out, this had to be held much closer to my eye, at around 15cm. The 60mm print-out had to positioned about 180cm away from me for it to be of a comparable size to real life.
I did try the same with the 98mm print-out and this was around about 4m but it was getting tricky to judge by then, especially as the wind was really picking up and the image was stuck on the top of my tripod!
Incidentally, whilst sizing up this shoot, I was confronted by a security guard who cautioned me not to take photographs of the house (visible on the left of the 18mm image) as it's a 'royal residence'. I hope I can get away with 3 windows and a fence!