I am new to the photography field and this something which I am not able to understand. I am playing around with my Nikon D90 along with its kit lens (18-105mm).
While reading about Depth of preview, the author asks to do some basic exercise to better understand DOF, like this:
- set your aperture to smallest number f/2.8, f/3.5, f/4 with 70mm or longer lens.
When I tried to set aperture to f/3.5, and tried to change focal length, my camera is setting aperture automatically in every every possible mode (which I know of). It is changing aperture in the following fashion:
- 18-24 ----> 3.4 to 4
- 18-35 ----> 4.5
- 18-50 ----> 5
- 18-105 ---> 5.6
But if i set my aperture to 5.6 or higher, it does not change when I change the focal length of my camera. I know I am not doing some basic thing right, but I'm still not sure why this is happening. Might some one help me to understand this?