d90 Autofocus problem

[farmerj]

I can pick any of the AF points on my D90 with no issue.

the AF-L/AE-L is menu dependent. You can set it for either Exposure lock or Focus Lock.

I use mine for Exposure lock. You place your focus point on the object you want to expose for, press the AE-L and then recompose to the picture you want to take.

The exposure is locked to when you pressed the button. Best way to see how this works is take a picture on a sunny day.

compose and lock the exposure on something on the ground. You will have a blown out sky.

Compose on the clouds and lock the exposure on them. Recompose on the same picture as before. You will have clouds that are correctly exposed, but your ground subject will be seriously under exposed depending on the day you are having.

I will do this when I am in a room and the exposure is getting mussed up due to different outfits that the camera is exposing for. I expose for something like a grey card, then just start taking pictures with the same lights from the room or event.

AF-S is Single focus. You need to re-press the shutter button to get it to refocus when something moves. Best for inanimate objects or if you want to use if kind of as a AF-L while the AE-L/AF-L button is programmed for AE-L.

AF-A is Auto Focus. The camera will decide if AF-C or AF-S is needed.

AF-C is continuous focus. The camera will continuously focus allowing you to track and follow your subject. Niece's walking across the stage for graduation is one example.