Depth-Of-Field Continued

In the previous post, I made a comment about relationship between Aperture (f-stop number) and depth-of-field. 

Small f number - Wide Opening(more light) - Shallow Depth-of-field

Big f number    - Small Opening (less light)  - Large Depth-of-Field

There is one more parameter which affects the Depth-Of-Field directly and that is the focal length used for the shot.

The 5 images above have been shot at 17 mm, 40 mm, 70 mm, 135 mm and 200 mm focal lengths - all at f/9! The distance between the camera and the object being clicked remained the same. As can be seen in the images, the higher focal lengths get you a shallow depth-of-field even at smaller aperture opening.

Ofcourse, the images above are "crops" - meaning the actual image that fills up my shot is much more than what can be seen above. At 17mm, there is quite a bit of "other things" which also come in the frame and which have been cropped for better comparison purpose. The left-most image has all 3 dolls sharp, the pillow and the remote control behind the dolls also showing good amount of detail. But by the time we move to the right-most image, except for the center doll, everything else gets blurred out!