D40 autofocusing

[ToluiAnda]

Hi all, I am using D40 with kit lens. When I point my camera towards some totally white background, it does not autofocus, and the shutter wont release. the same applies to totally blue background like the sky, when there is nothing else inside the frame. However, when i turned to manual focus mode, the shutter is able to release. Can someone tell me why? Thanks in advance.

[Squid]

Originally Posted by ToluiAnda Hi all, I am using D40 with kit lens. When I point my camera towards some totally white background, it does not autofocus, and the shutter wont release. the same applies to totally blue background like the sky, when there is nothing else inside the frame. However, when i turned to manual focus mode, the shutter is able to release. Can someone tell me why? Thanks in advance.

AF relies on sufficient contrast within the focus point to determine if the picture is in focus. When it is unable to focus, the camera will not release shutter when you press the shutter release button. When you switch to MF, you manually override the camera, so the camera release shutter when you press the shutter release button. More information related your question can be found at the these pages of the manual

1. On page 23 of D40 manual, you will see "Shutter can be released if camera is able to focus." for AF-S or AF-C or AF-A setting.
2. Ability for D40 camera to focus is mentioned on page 27 of the D40 manual which says "Autofocus does not perform well ... (when) ... There is little or no contrast between the subject and the background (e.g., the subject is the same color as the background). The focus area contains objects at different distances from the camera (e.g., the subject is inside a cage)."
3. On page 27 of the manual, it says that "If the camera is unable to focus using autofocus, use manual focus (see page 28) or use focus lock (see page 26) to focus on another subject at the same distance and then recompose the photograph."

[ToluiAnda]

Wah, Thanks for your detailed explanation. I shall read more.