Jonas: How come the background of the images looks different? Is that to do with characteristic of the lens? (I was under the impression that they should capture the same background)
Hi,
But why are you under that impression?
You can think about it in different ways: The two images are taken at different distances from the focal plane. The focal plane is at the metal ruler going across the image. The shooting distance(s) are adjusted so the image barely covers the Christmas tree decorations at the ends. The 20mm is wider than the 25 and so I had to be a bit closer when using the 20.
As the 20 is wider it has to see more, a wider field of view, than the 25. That is like sitting in a theatre close to the stage and look a little behind the curtains at the sides. You see more behind the curtains the closer to the stage you are.
You can also take a sheet of paper and make a simple drawing. Make a lens symbol to the left and something indicating my ruler with stuff on it in the center. Now draw two lines from the lens touching the ends of the symbol for the ruler and extend these lines to the right edge of the paper. At the right you see the are covered by the 25mm lens.
Now make another lens symbol a bit closer to the ruler symbol and again draw the two lines. At the right you see what area is covered by the 20mm lens.
The ruler is always depicted the same size as the shooting distance is adjusted for the lens' enlarging capabilities. That's the same as we are moving a bit to cover... let's say two friends standing in front of us and we want to take a head and shoulder image of them. With the 20 we are a bit closer to cover the scene, with the 25 we step back (increasing the distance with 25% in this case) and get the same shot. The backgrounds will differ in the same was as in the images above.
I hope this makes some sense and explain what you see in the images,
regards,
/Jonas
