For exercise 1 I took a walk along the Basingstoke canal to the lock that is between North Town and Ash Vale. Initially I went behind the house to the river there but because of the time of year there is so much new greenery sprouting that there really was not enough room to do this test and the pictures looked rather dull.  I thought the Lock gates would make a nice subject for this test.

Equipment: I used my Canon EOS 7D fitted with an EF 28 to 200 mm f5.6 Zoom lens.

I set the zoom to the point where the image looked the same to my open eye as it did through the viewfinder, this lead me to my first discovery. I was expecting the standard focal length to be different to the 50mm that was the norm on 35mm cameras because I had read that the sensor size of the camera would change this ratio and it only worked on so-called full frame sensor cameras. However the lens was at 50mm on the dial and the meta data on the file confirms this. I will now have to go ahead and investigate this further to fully understand this relationship.

Here is the Image at 50mm Focal Length (Standard):

f/5.6 1/160sec ISO200 50mm

Next I zoomed the lens to its minimum focal length of 28mm and took the second image

Here is the Image at 28mm Focal Length (Wide Angle):

f/5.6 1/160sec ISO200 28mm

Next I zoomed the lens to its maximum focal length of 200mm and took the third image

Here is the Image at 200mm Focal Length (Telephoto):

f/5.6 1/80sec ISO200 200mm

It is clear from this experiment that the shorter the focal length the wider the angle of view i.e. smaller the image and therefore more of the scene fills the image.

When extending the focal length the image gets larger and appears closer therefore les of the scene fills the image.

I printed out the images and returned to the scene, I found that the standard image i could just about get to match the size of the scene by holding it at the extent of my reach. I found that I had to get about an inch from the paper in the case of the 28mm print and that I would need to have taken an assistant to make the telephoto one work as it was far beyond the reach of my arm.

NOTE: I need to do some reasearch into my camera to establish the sensor size and the relationship to the focal length.

QUESTION: What is the standard focal length mathematically and how do I calculate it?