Exercise 1: Focal Length and Angle of View

This is actually the first exercise out of the book but unfortunately a difficult one because it requires printing and walking with the prints. This exercise requires taking 3 photographs of the same screen on the same spot. The three images will be zoomed at different focal length. I have two tasks here:

1) Look through the viewfinder compare the size of the image by not looking through viewfinder. Find the focal length that roughly two visions are equal in size.

2) Print the images on an A4, then hold them against the actual screen. Move them back and forth until the size is roughly the same as the actual screen.

The lens I use is the 24-70mm f/2.8 and the actual screen is a nearby church (Nice ceiling by the way, I wish I have a ultra-wide that can capture it along with the screen below). So I will zoom at 24mm and 70mm and find the one focal point that the size is similar. 

Image 1: 28mm f/2.8 ISO 3200 at 1/80s

Image 2: 48mm f/2.8 ISO 3200 at 1/80s

Image 3: 70mm f/3.2 ISO 3200 at 1/80s

Because it is indoor and I didn't use flash, the ISO is quite high and I have the aperture open wide. I choose to focus at the text at the end because it is common to three images. I have thought of focusing at the lamp instead, but it's position is too high at the image that I zoom in. I don't like the effect.


The last part of exercise requires me to print out the three pictures on A4, stand at where I was taking the pictures and move them back and forth to see which one appear to be the same size as real life. It is hard to measure distance here given I don't have a ruler at all. The idea should be something like this. We can check an optic text book on the definition of magnification and it is focal length/(distance to object - focal length). For the object I shoot here, the distance is much larger than focal length of the lens, so the magnification (A4 paper/ actual size) is roughly focal length/distance to object. As a result, we see lens with longer focal length will give a bigger magnification and these are telephoto lens. Vice versa.