Introduction: Exercise 1
Focal length and angle of view
The first exercise involved using a zoom lens (in this case a Canon 24-105mm f/4 L IS) to match the size of the image in the viewfinder with the size of the image as seen with the (other!) naked eye. The answer, read from the lens barrel, was about 54mm, so not far off from a ‘standard’ lens view, considered to be a nominal 50mm. A single image was taken.
The lens was then set to its widest (24mm) and narrowest (105mm) angle of view and one further photograph taken at each setting. The images were clearly smaller and larger than the ‘standard’ view respectively.
Prints of each of the three images (just inkjet copies on ordinary paper) were made and the ‘standard’ images held up to the eye whilst standing in the same location from where the pictures were taken, and a measurement made of the viewing distance; this was 47cm. The print of the image taken at 24mm needed to be held much closer to make it appear the same size as the actual view .. far too close for my eyesight, but probably about 25cm or so! The print made from the image taken at 105mm needed to be held much further away to match the size of the view, certainly more than arms length.
Although I have obviously looked at many scenes at different focal lengths before, this exercise was interesting because of the work with the actual prints to match the wide and narrow angle of view images with the ‘standard’ view. I used a tree as a ready way of scaling the images by eye – not a very interesting tree, so I have not attached the actual images, especially as the impact of focal length crops up in more detail in ‘Part One : The Frame’ later on.
All images were taken at f/4 and 1/250sec at ISO200.